Method for improving generation efficiency of third harmonic
阅读说明：本技术 一种用于提高三次谐波产生效率的方法 (Method for improving generation efficiency of third harmonic ) 是由 尹雨松 于 2019-10-16 设计创作，主要内容包括：本发明公开了一种用于提高三次谐波产生效率的方法,包括以下步骤：1)设置三次谐波产生的装置；2)产生基频激光束并对其进行加强反射；3)进行垂直反射或倾斜反射；4)对基频激光束进行反射,使得基频激光束沿公共轴二向前传输；5)加强二次谐波光束和三次谐波光束发射。本发明属于激光技术领域,具体是指一种用于提高三次谐波产生效率的方法。(The invention discloses a method for improving the generation efficiency of third harmonic, which comprises the following steps: 1) a third harmonic generation device is arranged; 2) generating a fundamental frequency laser beam and performing reinforced reflection on the fundamental frequency laser beam; 3) performing vertical reflection or oblique reflection; 4) reflecting the fundamental frequency laser beam to enable the fundamental frequency laser beam to be transmitted forwards along the common axis II; 5) enhancing the second harmonic beam and third harmonic beam emissions. The invention belongs to the technical field of laser, and particularly relates to a method for improving generation efficiency of third harmonic.)
1. A method for generating third harmonic laser with high optical conversion efficiency is characterized by comprising the following steps:
1) the third harmonic generation device is arranged: the third harmonic generation device comprises an optical cavity, a laser medium, a laser pump, a first fundamental frequency high reflector, a Q switch, a spherical lens, a cylindrical lens, an adjustable reflector, a first multiple wave reflection enhanced output device and a third harmonic enhanced reflector, wherein the laser medium, the laser pump, the first fundamental frequency high reflector, the Q switch, the spherical lens, the cylindrical lens, the adjustable reflector, the multiple wave reflection enhanced output device and the third harmonic enhanced reflector are all arranged in the optical cavity, the laser medium, the laser pump, the first fundamental frequency high reflector, the Q switch, the spherical lens, the cylindrical lens and the adjustable reflector are sequentially arranged along the horizontal direction, the laser medium, the laser pump, the first fundamental frequency high reflector, the Q switch, the spherical lens, the cylindrical lens and the adjustable reflector are arranged on the same horizontal common axis, the multiple wave reflection enhanced output device is arranged right below the adjustable reflector, the third harmonic wave reinforced reflection device and the multiple wave reflection reinforced output device are sequentially arranged in the horizontal direction, the third harmonic wave reinforced reflection device and the multiple wave reflection reinforced output device are arranged on the same horizontal common shaft II along the horizontal central axis, the multi-wave reflection enhancing output device is a multi-wave high reflection lens which is arranged below the adjustable reflector, the third harmonic enhanced reflection device comprises a light beam high reflection lens, an I-type nonlinear second harmonic crystal and an II-type nonlinear third harmonic crystal, the multi-wave high-reflection lens, the light beam high-reflection lens, the I-type nonlinear second harmonic crystal and the II-type nonlinear third harmonic crystal are sequentially arranged along the horizontal direction, the horizontal central axes of the light beam high-reflection lens, the I-type nonlinear second harmonic crystal, the II-type nonlinear third harmonic crystal and the multi-wave high-reflection lens are arranged on a same horizontal common axis II;
2) the laser medium is used for generating a base frequency laser beam to be emitted to the front end and the rear end along a common axis, the laser pump is used for exciting the laser medium, the base frequency laser beam is transmitted forwards to reach the spherical lens and further forwards to reach the cylindrical lens and the Q switch, the spherical lens adjusts the spot size of the light beam, the cylindrical lens compensates the thermal lens characteristic of the crystal, in the Q switch option, the laser is restrained by introducing loss in the resonant cavity, meanwhile, the energy pump is pumped and stored in the population inversion, once the required population inversion is obtained, the loss is reduced to allow the laser to be emitted, in the mode, large pulse train output can be generated from the laser, the base frequency laser beam is transmitted backwards to the adjustable reflector, the adjustable reflector reflects a part of the base frequency laser beam to the base frequency laser beam of the base frequency high reflector along the common axis and then reaches the base frequency laser beam of the base frequency high reflector, the fundamental frequency high reflector reflects the laser beam, the fundamental frequency laser beam reaches the adjustable reflector, and the adjustable reflector oscillates with the optical output of the front end fundamental frequency high reflector I from the laser medium;
3) The inclination angle of the reflector can be adjusted manually to enable the reflector to vertically reflect the fundamental frequency laser beam or obliquely reflect the fundamental frequency laser beam;
4) The fundamental frequency laser beam is vertically reflected by the adjustable reflector to reach the multi-wave high-reflection mirror, and the multi-wave high-reflection mirror reflects the fundamental frequency laser beam so that the fundamental frequency laser beam is transmitted forwards along the common axis II;
5) the reflected fundamental laser beam passing through the multi-wave high-reflection mirror reaches the II-type nonlinear third harmonic crystal, the II-type nonlinear third harmonic crystal oscillates with the light beam reflected by the multi-wave high-reflection mirror, the output of the II-type nonlinear third harmonic crystal points to the I-type nonlinear second harmonic crystal for generating second harmonic, the output of the I-type nonlinear second harmonic crystal points to the light beam high-reflection mirror, and the fundamental light beam is converted into the third harmonic light beam by the II-type nonlinear third harmonic crystal only under the condition that the second harmonic light beam exists, so the fundamental laser beam is not influenced when passing through the II-type nonlinear third harmonic crystal; a small part of fundamental frequency laser beam is converted into horizontally polarized second harmonic beam phase matching (crystal orientation) or non-critical phase matching (temperature tuning) through an I-type nonlinear second harmonic crystal by satisfying the phase matching condition (K (2w) ═ K (w) + K (w)), the fundamental frequency laser beam and the second harmonic beam are both transmitted towards a beam highly reflecting mirror and reflected back from the same mirror, when the fundamental frequency laser beam passes through the I-type nonlinear second harmonic crystal when reflected from the beam highly reflecting mirror, the other small part of fundamental frequency laser beam passes through the I-type nonlinear second harmonic crystalThe light beam is converted into a second harmonic beam, the second harmonic beam is superposed with the reflected second harmonic beam to form a combined second harmonic beam, and the II-type nonlinear third harmonic crystal meets the phase matching condition of k (3W)1/2(K (W) + K (2W)) converting a portion of the fundamental laser beam and most of the second harmonic beam delivered from the type I nonlinear second harmonic crystal into a third harmonic beam; the fundamental frequency laser beam, the second harmonic beam and the third harmonic beam are directed to the multiple wave high reflection mirror, the multiple wave high reflection mirror removes the third harmonic beam from the cavity, reflects the second harmonic beam to the adjustable reflection mirror, and can be output from the optical cavity together as the second harmonic beam and the third harmonic beam, and the conversion efficiency is 25% to 50%.
2. The method as claimed in claim 1, wherein the multiple-wave reflection enhanced output device comprises a first prism, a second prism, a guiding lens and a second harmonic emitter, wherein the vertex angles of the first prism and the second prism are obliquely arranged on one side of the adjustable reflecting mirror close to the laser pump, the first prism is arranged above the second prism, the guiding lens is arranged right above the first prism, the second harmonic generator is arranged on one side of the adjustable reflector principle laser pump, the second harmonic emitter is arranged between the adjustable reflecting mirror and the guiding lens, and the second prism and the type II nonlinear third harmonic crystal are arranged on the same horizontal line.
3. The method for generating a third harmonic laser with high light conversion efficiency as claimed in claim 1, wherein the step 4) of obliquely reflecting the fundamental laser beam via the adjustable mirror reaches a first prism and a second prism, and the first prism and the second prism deflect and guide the fundamental laser beam to the type II nonlinear third harmonic crystal.
4. The method for generating a third harmonic laser having a high light conversion efficiency as claimed in claim 1, wherein the first and second prisms of step 5) deflect the fundamental beam andThe fundamental laser beam is guided to the II type nonlinear third harmonic crystal, the output of the II type nonlinear third harmonic crystal points to the I type nonlinear second harmonic crystal used for generating the second harmonic, the output of the I type nonlinear second harmonic crystal points to the light beam high reflection lens, and the fundamental light beam is converted into the third harmonic light beam by the II type nonlinear third harmonic crystal only under the condition that the second harmonic light beam exists, so the fundamental laser beam is not influenced when passing through the II type nonlinear third harmonic crystal; a small portion of the fundamental laser beam is converted into a horizontally polarized second harmonic beam by a type I nonlinear second harmonic crystal by satisfying a phase matching condition (K (2W) ═ K (W) + K (W)) by a type I nonlinear second harmonic crystal, the fundamental laser beam and the second harmonic beam are transmitted toward a beam highly reflecting mirror and reflected back from the same mirror, while the fundamental laser beam passes through a type I nonlinear second harmonic crystal upon reflection from the beam highly reflecting mirror, another small portion of the fundamental laser beam is converted into a second harmonic beam thereof, the second harmonic beam is superimposed with the reflected second harmonic beam to form a combined second harmonic beam, and a type II nonlinear third harmonic crystal is converted into a second harmonic beam upon satisfying a phase matching condition K (3W) °1/2(K (W) + K (2W)) converting a portion of the fundamental laser beam and a majority of the second harmonic beam transmitted from the type I nonlinear second harmonic crystal into a third harmonic beam, the fundamental laser beam, the second harmonic beam, and the third harmonic beam entering a second prism where the beams are shifted from one to another, the shifted beams entering the first prism increasing the displacement between the beams, the fundamental laser beam exiting the first prism being directed to an adjustable mirror and reflected back to the laser medium, the directing mirror reflecting the third harmonic beam and the second harmonic beam and reflecting the beams out of the optical cavity, the second harmonic emitter to block the second harmonic beam from the output.
5. The method according to claim 1, wherein the third harmonic enhanced reflector comprises a beam high-reflection mirror, a type I nonlinear second harmonic crystal, a type II nonlinear third harmonic crystal, and a wave plate, the beam high-reflection mirror, the type I nonlinear second harmonic crystal, the type II nonlinear third harmonic crystal, and the wave plate are sequentially arranged along a horizontal direction, the beam high-reflection mirror, the type I nonlinear second harmonic crystal, the type II nonlinear third harmonic crystal, and the wave plate are disposed on a same horizontal common axis, and the wave plate is disposed between the type II nonlinear third harmonic crystal and the multi-wave high-reflection mirror.
6. the method of claim 1, wherein the step 5) of obtaining improved recovery of the third harmonic beam from the laser cavity if the polarization of the third harmonic beam with the multi-wave high-reflection mirror is "P" polarization, the fundamental laser beam is vertically reflected by the adjustable mirror with vertical polarization, then the fundamental laser beam is reflected by the multi-wave high-reflection mirror and passes through the wave plate, the wave plate rotates the fundamental laser beam to an integer of full wave or full wave, the polarization of the fundamental laser beam is unchanged, the fundamental laser beam passes through the type II nonlinear third harmonic crystal and is not affected without the second harmonic beam, a portion of the fundamental laser beam is converted to the second harmonic on the type I nonlinear second harmonic crystal, and the polarization of the fundamental laser beam is kept vertical polarization, the resulting second harmonic beam is horizontally polarized, the beam highly reflective optic reflects the fundamental and second harmonics through the type I nonlinear second harmonic crystal, a further portion of the fundamental laser beam is converted to a horizontally polarized second harmonic, the fundamental laser beam and the second harmonic are directed through the type II nonlinear third harmonic crystal, which requires that the fundamental laser beam and the second harmonic beam occur on the crystal with orthogonal polarizations to each other, a portion of the fundamental laser beam and a major portion of the second harmonic are converted to a third harmonic beam having the same polarization as the fundamental laser beam, in this case vertical polarization, the beam leaving the type II nonlinear third harmonic crystal is directed through a waveplate, which performs a 1/2 wave rotation on the third harmonic beam to convert its polarization to horizontal polarization before an accident occurs on its multiple wave highly reflective optic, the multi-wave high-reflectivity mirror will remove substantially all of the third harmonic beam from the laser cavity.
7. The method according to claim 1, wherein the third harmonic enhanced reflection device comprises a light beam high reflection mirror, an I-type doubling crystal, an I-type frequency tripling crystal, and a wave plate, the light beam high reflection mirror, the I-type doubling crystal, the wave plate, and the I-type frequency tripling crystal are sequentially arranged along a horizontal direction, horizontal central axes of the light beam high reflection mirror, the I-type doubling crystal, the wave plate, and the I-type frequency tripling crystal are disposed on a same horizontal common axis two, and the wave plate is disposed between the I-type frequency tripling crystal and the I-type frequency tripling crystal.
8. The method for generating a third harmonic laser with high light conversion efficiency as claimed in claim 1, wherein the step 5) the fundamental laser beam with vertical polarization is reflected by the adjustable mirror to the multiple wave high reflection mirror, reflected by the type I frequency tripling crystal and the wave plate, the fundamental laser beam is not affected when passing through the type I frequency tripling crystal, unless the second harmonic beam is polarized in parallel with the fundamental laser beam, the crystal has no effect on the fundamental laser beam, the fundamental laser beam passes through the wave plate with its polarization unchanged, the beam is generated on the type I frequency doubling crystal, the type I frequency doubling crystal converts a part of the fundamental laser beam into a horizontally polarized second harmonic beam, the fundamental laser beam and the second harmonic beam are reflected from the beam high reflection mirror back to the type I frequency doubling crystal, wherein a part of the fundamental laser beam is converted into a horizontally polarized second harmonic beam, and when passing through the wave plate, the polarization of the second harmonic beam is rotated by one half wave, the fundamental and second harmonic beams have polarization relatively parallel to each other, which is necessary for an I-type triple crystal for third harmonic conversion, a part of the fundamental laser beam and most of the second harmonic are converted into a third harmonic beam and exit the I-type triple crystal, the generated third harmonic will be horizontally polarized, and then the horizontally polarized third harmonic is incident on a multiple-wave high-reflection mirror oriented such that the horizontally polarized beam will be P-polarized to the multiple-wave high-reflection mirror, the P-polarized third harmonic will be substantially completely transmitted through the multiple-wave high-reflection mirror, and the unconverted fundamental beam will be reflected due to the multiple-wave high-reflection mirror being reflective to the fundamental laser beam.
9. The method as claimed in claim 1, wherein an optical resonator is formed between the first high-reflection mirror with fundamental frequency and the second high-reflection mirror with beam, the adjustable mirror can adjust its angle, the adjustable mirror is a folded mirror, the laser medium can be pre-selected, the cylindrical lens has thermal lens characteristics of a compensation crystal, the spherical lens is used for adjusting the spot size of the beam, the first high-reflection mirror with fundamental frequency is a high-reflection mirror with laser medium fundamental frequency, the type I nonlinear second harmonic crystal is used for second harmonic generation, the type II nonlinear third harmonic crystal is used for third harmonic generation, the beam high-reflection mirror is a high-reflection mirror with fundamental frequency and second harmonic frequency spectrum, the first high-reflection mirror and the beam high-reflection mirror are used for defining an optical cavity, the multi-wave high-reflection lens is a dichroic mirror, the I-type nonlinear second harmonic crystal is an I-type LBO crystal, and the II-type nonlinear third harmonic crystal is a II-type lithium triborate crystal.
10. the method for generating a third harmonic laser with high light conversion efficiency as claimed in claim 1, wherein the first and second prisms are UV graded fused siliconized prisms I and II.
Technical Field
The invention belongs to the technical field of laser, and particularly relates to a method for improving generation efficiency of third harmonic.
Background
The common third harmonic solid laser is produced outside the laser resonant cavity, one infrared laser is used as light source, the output infrared laser as fundamental wave is injected into the frequency doubling nonlinear crystal to produce second harmonic light, the frequency doubling light and unconverted fundamental wave light act on the third harmonic nonlinear crystal to mix frequency to produce third frequency doubling laser and outputalthough the third harmonic light generated by this method is stable and easy to debug, because the incident fundamental power is low, the output coupling ratio of the infrared laser generation technology is about 20%, and the harmonic efficiency is proportional to the square of the incident fundamental power, so the conversion efficiency is limited by the extra-cavity harmonic, in order to improve the conversion efficiency of the extra-cavity harmonic, lens focusing is usually adopted to enhance the power density of the fundamental, but the condensed light beam will cause the damage of the optical anti-reflection film layer on the surface of the nonlinear crystal and the crystal itself, so that the total output power of the harmonic is limited, the frequency mixing outside the cavity is a single-pass behavior, i.e. the fundamental and the second harmonic pass through the triple frequency doubling crystal once, the fundamental and the second harmonic which are not converted into the third harmonic are all wasted, so that the triple frequency effect of the third harmonic solid laser is difficult to achieve simultaneously, for the high power laser, the typical efficiency is limited to be less than 25% of the total conversion, since the unconverted fundamental and second harmonic beams are wasted in this structure, even if it is a very high power pulse Nd: YAG laser, the total conversion efficiency is lower than 25%; the theory behind intracavity second harmonic generation has been elucidated, with the crystal medium producing the second harmonic of the incident radiation frequency, the tensor d in the lowest order nonlinear polarization term, only if the crystal lacks inversion symmetry to polarize the second orderijdoes not disappear, if the crystal has inverted symmetry, the lowest order nonlinear polarization contribution is cubic in the electric field strength, and the crystal will produce only third or higher harmonics of the initial frequency.
disclosure of Invention
In order to solve the above problems, the present invention provides a method for generating third harmonic laser with high optical conversion efficiency.
The technical scheme adopted by the invention is as follows: a method for improving third harmonic generation efficiency, comprising the steps of:
1) The third harmonic generation device is arranged: the third harmonic generation device comprises an optical cavity, a laser medium, a laser pump, a first fundamental frequency high reflector, a Q switch, a spherical lens, a cylindrical lens, an adjustable reflector, a first multiple wave reflection enhanced output device and a third harmonic enhanced reflector, wherein the laser medium, the laser pump, the first fundamental frequency high reflector, the Q switch, the spherical lens, the cylindrical lens, the adjustable reflector, the multiple wave reflection enhanced output device and the third harmonic enhanced reflector are all arranged in the optical cavity, the laser medium, the laser pump, the first fundamental frequency high reflector, the Q switch, the spherical lens, the cylindrical lens and the adjustable reflector are sequentially arranged along the horizontal direction, the laser medium, the laser pump, the first fundamental frequency high reflector, the Q switch, the spherical lens, the cylindrical lens and the adjustable reflector are arranged on the same horizontal common axis, the multiple wave reflection enhanced output device is arranged right below the adjustable reflector, the third harmonic enhanced reflection device and the multiple wave reflection enhanced output device are sequentially arranged in the horizontal direction, the horizontal central axis of the third harmonic enhanced reflection device and the horizontal central axis of the multiple wave reflection enhanced output device are arranged on the same horizontal common axis II, the third harmonic enhanced reflection device is used for high reflection of fundamental frequency and second harmonic frequency spectrums and simultaneously generating third harmonic, the multiple wave reflection enhanced output device is a multiple wave high reflection lens which is arranged below an adjustable reflection lens and provides optical back and forth for the adjustable reflection lens, the multiple wave high reflection lens is used for high reflection of high transmission light beams of preselection fundamental frequency and third harmonic frequency light beams and simultaneously used for high reflection of second harmonic wavelength light beams, the third harmonic enhanced reflection device comprises a light beam high reflection lens, an I-type nonlinear second harmonic crystal and an II-type nonlinear third harmonic crystal, the multi-wave high-reflection lens, the light beam high-reflection lens, the I-type nonlinear second harmonic crystal and the II-type nonlinear third harmonic crystal are sequentially arranged along the horizontal direction, and the horizontal central axes of the light beam high-reflection lens, the I-type nonlinear second harmonic crystal, the II-type nonlinear third harmonic crystal and the multi-wave high-reflection lens are arranged on the same horizontal common axis II;
2) the laser medium is used for generating a base frequency laser beam to be emitted to the front end and the rear end along a common axis, the laser pump is used for exciting the laser medium, the base frequency laser beam is transmitted forwards to reach the spherical lens and further forwards to reach the cylindrical lens and the Q switch, the spherical lens adjusts the spot size of the light beam, the cylindrical lens compensates the thermal lens characteristic of the crystal, in the Q switch option, the laser is restrained by introducing loss in the resonant cavity, meanwhile, the energy pump is pumped and stored in the population inversion, once the required population inversion is obtained, the loss is reduced to allow the laser to be emitted, in the mode, large pulse train output can be generated from the laser, the base frequency laser beam is transmitted backwards to the adjustable reflector, the adjustable reflector reflects a part of the base frequency laser beam to the base frequency laser beam of the base frequency high reflector along the common axis and then reaches the base frequency laser beam of the base frequency high reflector, the fundamental frequency high reflector reflects the laser beam, the fundamental frequency laser beam reaches the adjustable reflector, and the adjustable reflector oscillates with the optical output of the front end fundamental frequency high reflector I from the laser medium;
3) The inclination angle of the reflector can be adjusted manually to enable the reflector to vertically reflect the fundamental frequency laser beam or obliquely reflect the fundamental frequency laser beam;
4) The fundamental frequency laser beam is vertically reflected by the adjustable reflector to reach the multi-wave high-reflection mirror, and the multi-wave high-reflection mirror reflects the fundamental frequency laser beam so that the fundamental frequency laser beam is transmitted forwards along the common axis II;
5) The reflected fundamental laser beam passing through the multi-wave high-reflection mirror reaches the II-type nonlinear third harmonic crystal, the II-type nonlinear third harmonic crystal oscillates with the light beam reflected by the multi-wave high-reflection mirror, the output of the II-type nonlinear third harmonic crystal points to the I-type nonlinear second harmonic crystal for generating second harmonic, the output of the I-type nonlinear second harmonic crystal points to the light beam high-reflection mirror, and the fundamental light beam is converted into the third harmonic light beam by the II-type nonlinear third harmonic crystal only under the condition that the second harmonic light beam exists, so the fundamental laser beam is not influenced when passing through the II-type nonlinear third harmonic crystal; a small portion of the fundamental laser beam is converted into horizontally polarized second harmonic beam phase matching (crystal orientation) or non-critical phase matching (temperature tuning) by the type I nonlinear second harmonic crystal by satisfying its phase matching condition (K (2w) ═ K (w) + K (w)), both the fundamental laser beam and the second harmonic beam are transmitted toward the beam highly reflective mirror and reflected back from the same mirror, when the fundamental laser beam passes through the type I nonlinear second harmonic crystal while being reflected from the beam highly reflective mirror,Another small part of fundamental laser beam is converted into second harmonic beam, which is superposed with the reflected second harmonic beam to form combined second harmonic beam, and the type-II nonlinear third harmonic crystal satisfies phase matching condition k (3W)1/2(K (W) + K (2W)) converting a portion of the fundamental laser beam and most of the second harmonic beam delivered from the type I nonlinear second harmonic crystal into a third harmonic beam; the fundamental laser beam, the second harmonic beam and the third harmonic beam are directed to a multi-wave high-reflection mirror, which removes the third harmonic beam from the cavity, reflects the second harmonic beam to an adjustable mirror, and can be output from the optical cavity together as the second harmonic beam and the third harmonic beam, with a conversion efficiency of 25% to 50%, preferably 50% or higher.
Further, output device is strengthened in multiple wave reflection includes prism one, prism two, direction lens and second harmonic transmitter, one and two apex angles of prism meet the slope and locate one side that adjustable speculum is close to the laser pump, the oblique top of prism two is located to prism one, the direction lens is located directly over the prism one, one side of adjustable reflector principle laser pump is located to the second harmonic generator, the second harmonic transmitter is located between adjustable speculum and the direction lens, prism two and II type nonlinear third harmonic crystal locate on same water flat line.
further, the obliquely reflected fundamental laser beam passing through the adjustable mirror in step 4) reaches the first prism and the second prism, which deflect and guide the fundamental beam to the type II nonlinear third harmonic crystal.
Further, step 5) the first and second prisms deflect and direct the fundamental beam to a type II nonlinear third harmonic crystal, the type II nonlinear third harmonic crystal output being directed to a type I nonlinear second harmonic crystal for second harmonic generation, the type I nonlinear second harmonic crystal output being directed to a beam highly reflective mirror, the fundamental laser beam passing through the type II nonlinear third harmonic crystal converting the fundamental beam to a third harmonic beam only in the presence of the second harmonic beamThe third harmonic crystal is not affected; a small portion of the fundamental laser beam is converted into a horizontally polarized second harmonic beam by a type I nonlinear second harmonic crystal by satisfying a phase matching condition (K (2W) ═ K (W) + K (W)) by a type I nonlinear second harmonic crystal, the fundamental laser beam and the second harmonic beam are transmitted toward a beam highly reflecting mirror and reflected back from the same mirror, while the fundamental laser beam passes through a type I nonlinear second harmonic crystal upon reflection from the beam highly reflecting mirror, another small portion of the fundamental laser beam is converted into a second harmonic beam thereof, the second harmonic beam is superimposed with the reflected second harmonic beam to form a combined second harmonic beam, and a type II nonlinear third harmonic crystal is converted into a second harmonic beam upon satisfying a phase matching condition K (3W) °1/2(K (W) + K (2W)) converting a portion of the fundamental laser beam and a majority of the second harmonic beam transmitted from the type I nonlinear second harmonic crystal into a third harmonic beam, the fundamental laser beam, the second harmonic beam, and the third harmonic beam entering a second prism where the beams are shifted from one to another, the shifted beams entering the first prism increasing the displacement between the beams, the fundamental laser beam exiting the first prism being directed to an adjustable mirror and reflected back to the laser medium, the directing mirror reflecting the third harmonic beam and the second harmonic beam and reflecting the beams out of the optical cavity, the second harmonic emitter to block the second harmonic beam from the output.
Furthermore, the third harmonic enhanced reflection device comprises a light beam high reflection lens, an I-type nonlinear second harmonic crystal, an II-type nonlinear third harmonic crystal and a wave plate, wherein the light beam high reflection lens, the I-type nonlinear second harmonic crystal, the II-type nonlinear third harmonic crystal and the wave plate are sequentially arranged along the horizontal direction, the horizontal central axes of the light beam high reflection lens, the I-type nonlinear second harmonic crystal, the II-type nonlinear third harmonic crystal and the wave plate are arranged on the same horizontal common axis II, and the wave plate is arranged between the II-type nonlinear third harmonic crystal and the multi-wave high reflection lens.
further, if the polarization of the third harmonic beam with the multi-wave high reflection mirror is "P" polarization as described in step 5), improved recovery of the third harmonic beam from the laser cavity can be obtained, the fundamental laser beam is vertically reflected by the adjustable mirror under vertical polarization, then the fundamental laser beam is reflected by the multi-wave high reflection mirror and passes through the wave plate, the wave plate rotates the fundamental laser beam to an integer of full wave or full wave, the polarization of the fundamental laser beam is not changed, the fundamental laser beam passes through the type II nonlinear third harmonic crystal, without being affected by the second harmonic beam, a portion of the fundamental laser beam on the type I nonlinear second harmonic crystal is converted to a second harmonic, the polarization of the fundamental laser beam remains vertically polarized, and the resulting second harmonic beam is horizontally polarized, the beam high reflection mirror reflects the fundamental and second harmonics through the type I nonlinear second harmonic crystal, a further portion of the fundamental laser beam is converted to a horizontally polarized second harmonic, the fundamental laser beam and the second harmonic are directed through a type II nonlinear third harmonic crystal, which requires the fundamental laser beam and the second harmonic beam to occur in orthogonal polarizations on the crystal, a portion of the fundamental laser beam and a major portion of the second harmonic are converted to a third harmonic beam having the same polarization as the fundamental laser beam, in this case vertical polarization, the beam exiting the type II nonlinear third harmonic crystal is directed through a waveplate, which performs a 1/2 wave rotation on the third harmonic beam to convert its polarization to horizontal polarization before an incident occurs on its multi-wave highly reflective optic, which will remove substantially all of the third harmonic beam from the laser cavity.
Furthermore, the third harmonic enhanced reflection device comprises a light beam high reflection lens, an I-type doubling crystal, an I-type frequency tripling crystal and a wave plate, wherein the light beam high reflection lens, the I-type doubling crystal, the wave plate and the I-type frequency tripling crystal are sequentially arranged along the horizontal direction, the I-type frequency tripling crystal is an I-type BBO or LBO crystal or the like, horizontal central axes of the light beam high reflection lens, the I-type doubling crystal, the wave plate and the I-type frequency tripling crystal are arranged on the same horizontal common axis II, and the wave plate is arranged between the I-type frequency tripling crystal and the I-type doubling crystal.
Further, step 5) the fundamental laser beam having vertical polarization is reflected by the adjustable mirror to the multiple-wave high reflection mirror, reflected by the type I triple frequency crystal and the wave plate, the fundamental laser beam is not affected when passing through the type I triple frequency crystal, the crystal has no effect on the fundamental laser beam unless the second harmonic beam is polarized in parallel with the fundamental laser beam, the polarization of the fundamental laser beam is unchanged by the wave plate, the beam occurs on the type I multiplier crystal, the type I multiplier crystal converts a part of the fundamental laser beam into a horizontally polarized second harmonic beam, the fundamental laser beam and the second harmonic are reflected from the beam high reflection mirror back to the type I multiplier crystal, wherein a part of the fundamental laser beam is converted again into a horizontally polarized second harmonic beam, the polarization of the second harmonic beam is rotated by one half wave while passing through the wave plate, the fundamental and second harmonic beams have polarization in parallel with respect to each other, this is necessary for a type I triple crystal for third harmonic conversion where a portion of the fundamental laser beam and most of the second harmonic are converted into a third harmonic beam and exit the type I triple crystal, the resulting third harmonic will be horizontally polarized and then the horizontally polarized third harmonic is incident on a multiple wave high reflection mirror oriented such that the horizontally polarized beam will be P-polarized to the multiple wave high reflection mirror, the P-polarized third harmonic will be substantially completely transmitted through the multiple wave high reflection mirror, and the unconverted fundamental beam will be reflected due to the multiple wave high reflection mirror being reflective to the fundamental laser beam.
Further, an optical resonant cavity is formed between the first fundamental frequency high-reflection mirror and the beam high-reflection mirror, the adjustable mirror can adjust the angle of the adjustable mirror, the adjustable mirror reflects the strengthened fundamental beam and is optionally a high-reflection device for the second harmonic frequency, the high-reflection device oscillates with the optical output of the fundamental beam from the laser medium, the downward reflection in the vertical direction can be realized according to the difference of the angle of the adjustable mirror, the downward reflection in the vertical direction can also be realized according to the difference of the angle of the adjustable mirror, the cylindrical lens has the thermal lens characteristic of a compensation crystal, the adjustable mirror is a folding mirror, the laser medium can be preselected, the spherical lens is used for adjusting the spot size of the beam, the first fundamental frequency high-reflection mirror is a high-reflection mirror for the fundamental frequency of the laser medium, the type I nonlinear second harmonic crystal is used for generating the second harmonic, the light beam high-reflection lens is a high-reflection lens with fundamental frequency and second harmonic frequency spectrums, the first high-reflection lens and the light beam high-reflection lens limit an optical cavity, the multi-wave high-reflection lens is a dichroic mirror, the I-type nonlinear second harmonic crystal is an I-type LBO crystal, and the II-type nonlinear third harmonic crystal is an II-type lithium triborate crystal.
Further, the first prism and the second prism are a UV-gradually-changed fused siliconized first prism and a UV-gradually-changed fused siliconized second prism.
The beneficial effects obtained by adopting the invention are as follows: compared with the method of the third harmonic outside the cavity, the laser equipment provided by the invention fully utilizes the strong fundamental wave light in the cavity, the strong fundamental wave light is reflected by the first fundamental frequency high reflector and the second fundamental frequency high reflector, the basic light beam is polarized perpendicular to the crystal axis, and the generated second harmonic beam is polarized parallel to the optical axis, the high transmission beam is reflected by the high reflection lens and the fundamental frequency and second harmonic high reflection lens, the fundamental beam and the second harmonic beam are orthogonally polarized and generate a third harmonic beam, the polarization of the polarization base beam and the polarization of the third harmonic beam, the polarization of which is parallel to one of the two input beams, are parallel, so that the conversion efficiency is improved, the second harmonic power is fully utilized for carrying out multiple frequency mixing, the efficiency and the power of the third harmonic are increased, the polarization optical coupling loss is reduced, and the beam quality and the stability of the third harmonic are improved.
Drawings
FIG. 1 is a schematic diagram of a laser apparatus for improving the efficiency of third harmonic generation according to the present invention;
FIG. 2 is a schematic diagram of an alternative embodiment of a laser apparatus for improving third harmonic generation efficiency in accordance with the present invention;
FIG. 3 is a graph of conversion efficiency of a laser apparatus for improving the efficiency of third harmonic generation in accordance with the present invention;
FIG. 4 is a schematic diagram of an alternative embodiment of a laser apparatus for improving third harmonic generation efficiency in accordance with the present invention;
Fig. 5 is a schematic diagram of an alternative embodiment of a laser apparatus for improving the efficiency of third harmonic generation according to the present invention.
The laser device comprises an optical cavity 1, an optical cavity 2, a type I doubling crystal 3, an adjustable reflector 4, a multiple wave reflection enhanced output device 5, a third harmonic enhanced reflection device 6, a laser medium 7, a laser pump 8, a first fundamental frequency high reflector 9, a Q switch 10, a spherical lens 11, a cylindrical lens 12, a multiple wave high reflector 13, a light beam high reflector 14, a type I nonlinear second harmonic crystal 15, a type II nonlinear third harmonic crystal 16, a first prism 17, a second prism 18, a guide lens 19, a second harmonic emitter 20, a wave plate 21 and a type I triple frequency crystal.
Detailed Description
The technical solutions of the present invention will be described in further detail with reference to specific implementations, and all the portions of the present invention that are not described in detail in the technical features or the connection relationships of the present invention are the prior art.
The invention relates to a method for generating third harmonic laser with high light conversion efficiency, which comprises the following steps:
1) the third harmonic generation device is arranged: the third harmonic generation device comprises an optical cavity 1, a laser medium 6, a laser pump 7, a first fundamental frequency high reflector 8, a Q switch 9, a spherical lens 10, a cylindrical lens 11, an adjustable reflector 3, a multiple wave reflection enhanced output device 4 and a third harmonic enhanced reflection device 5, wherein the laser medium 6, the laser pump 7, the first fundamental frequency high reflector 8, the Q switch 9, the spherical lens 10, the cylindrical lens 11, the adjustable reflector 3, the multiple wave reflection enhanced output device 4 and the third harmonic enhanced reflection device 5 are all arranged in the optical cavity 1, the laser medium 6, the laser pump 7, the first fundamental frequency high reflector 8, the Q switch 9, the spherical lens 10, the cylindrical lens 11 and the adjustable reflector 3 are sequentially arranged along the horizontal direction, and the laser medium 6, the laser pump 7, the first fundamental frequency high reflector 8, the Q switch 9, the spherical lens 10, Cylindrical lens 11 and 3 horizontal axis of adjustable speculum locate same horizontal commom one on, output device 4 is strengthened in the multiple wave reflection and locates under adjustable speculum 3, reflection device 5 is strengthened in the third harmonic and multiple wave reflection strengthen output device 4 horizontal direction and arrange in proper order, reflection device 5 is strengthened in the third harmonic and multiple wave reflection strengthen output device 4 horizontal axis locate same horizontal commom two on, output device 4 is strengthened in the multiple wave reflection for multiple wave high reflection lens 12, multiple wave high reflection lens 12 locates adjustable speculum 3 whole below, reflection device 5 is strengthened in the third harmonic includes light beam high reflection lens 13, I type nonlinear second harmonic crystal 14 and II type nonlinear third harmonic crystal 15, multiple wave high reflection lens 12, light beam high reflection lens 13, I type nonlinear second harmonic crystal 14 and II type nonlinear third harmonic crystal 15 arrange in proper order along the horizontal direction The horizontal central axes of the beam high-reflection mirror 13, the I-type nonlinear second harmonic crystal 14, the II-type nonlinear third harmonic crystal 15 and the multi-wave high-reflection mirror 12 are arranged on the same horizontal common axis II;
2) the laser medium 6 is used for generating a base frequency laser beam to be emitted to the front end and the back end along the common axis, the laser pump 7 is used for exciting the laser medium 6, the base frequency laser beam is transmitted forwards to the spherical lens 10 and further forwards to the cylindrical lens 11 and the Q switch 9, the spherical lens 10 adjusts the spot size of the laser beam, the cylindrical lens 11 compensates the thermal lens characteristic of the crystal, in the Q switch 9 option, the laser is restrained by introducing loss in a resonant cavity, energy pump is pumped and stored in population inversion, once the required population inversion is obtained, the loss is reduced to allow laser emission, in this mode, a large pulse train output can be generated from the laser, the base frequency laser beam is transmitted backwards to the adjustable reflector 3, the adjustable reflector 3 reflects a part of the base frequency laser beam to the base frequency high reflector one 8 along the common axis and then to the base frequency laser beam of the base frequency high reflector one 8, the first fundamental frequency high reflector 8 reflects the laser beam, the fundamental frequency laser beam reaches the adjustable reflector 3, and the adjustable reflector 3 oscillates with the optical output of the first front end fundamental frequency high reflector 8 from the laser medium 6;
3) the inclination angle of the reflector 3 can be adjusted manually to make the reflector vertically reflect the fundamental frequency laser beam or obliquely reflect the fundamental frequency laser beam;
4) The fundamental frequency laser beam is vertically reflected by the adjustable reflector 3 to reach the multi-wave high-reflection mirror 12, and the multi-wave high-reflection mirror 12 reflects the fundamental frequency laser beam so that the fundamental frequency laser beam is transmitted forwards along the second common axis;
5) The reflected fundamental laser beam passing through the multiple wave high reflection mirror 12 reaches the II type nonlinear third harmonic crystal 15, the II type nonlinear third harmonic crystal 15 oscillates with the light beam reflected by the multiple wave high reflection mirror 12, the output of the II type nonlinear third harmonic crystal 15 points to the I type nonlinear second harmonic crystal 14 for the generation of the second harmonic, the output of the I type nonlinear second harmonic crystal 14 points to the light beam high reflection mirror 13, because the II type nonlinear third harmonic crystal 15 converts the fundamental light beam into the third harmonic light beam only under the condition that the second harmonic light beam exists, the fundamental laser beam is not affected when passing through the II type nonlinear third harmonic crystal 15; a small part of the fundamental laser beam is converted into a horizontally polarized second harmonic beam by the type I nonlinear second harmonic crystal 14 through satisfying its phase matching condition (K (2W) ═ K (W) + K (W)) or non-critical phase matching (temperature tuning), the fundamental laser beam and the second harmonic beam are both transmitted toward the beam highly reflecting mirror 13 and reflected from the same mirror, when the fundamental laser beam passes through the type I nonlinear second harmonic crystal 14 upon reflection from the beam highly reflecting mirror 13, another small part of the fundamental laser beam is converted into its second harmonic beam which is superimposed with the reflected second harmonic beam to form a combined second harmonic beam, the type II nonlinear third harmonic crystal 15 satisfies the phase matching condition K (3W) ═ K (3W) —1/2(K (W) + K (2W)) converting a portion of the fundamental laser beam and most of the second harmonic beam delivered from the type I nonlinear second harmonic crystal 14 into a third harmonic beam; the fundamental laser beam, the second harmonic beam and the third harmonic beam are directed to the multiple wave high reflection mirror 12, the multiple wave high reflection mirror 12 removes the third harmonic beam from the cavity, reflects the second harmonic beam to the adjustable reflection mirror 3, and can be output from the optical cavity 1 together as the second harmonic beam and the third harmonic beam, and the conversion efficiency is 25% to 50%.
output device 4 is strengthened in multiple wave reflection includes prism 16, two 17 of prism, direction lens 18 and second harmonic transmitter 19, one 16 of prism and two 17 apex angles of prism meet the slope and locate adjustable speculum 3 and be close to one side of laser pump 7, the oblique top of two 17 of prism is located to one 16 of prism, direction lens 18 is located directly over one 16 of prism, one side of adjustable reflector principle laser pump 7 is located to the second harmonic generator, second harmonic transmitter 19 is located between adjustable speculum 3 and the direction lens 18, two 17 of prisms and II type nonlinear third harmonic crystal 15 locate on same water flat line.
Step 4) the obliquely reflected fundamental laser beam passing through the adjustable mirror 3 reaches the first prism 16 and the second prism 17, and the first prism 16 and the second prism 17 deflect the fundamental beam and guide it to the type II nonlinear third harmonic crystal 15.
Step 5) the first prism 16 and the second prism 17 deflect the fundamental wave beam and guide the fundamental wave beam to the II type nonlinear third harmonic crystal 15, the II type nonlinear third harmonic crystal 15 outputs and points to the I type nonlinear second harmonic crystal 14 used for generating the second harmonic, the I type nonlinear second harmonic crystal 14 outputs and points to the light beam high reflection lens 13, because the II type nonlinear third harmonic crystal 15 converts the fundamental wave beam into the third harmonic beam only under the condition that the second harmonic beam exists, the fundamental frequency laser beam is not influenced when passing through the II type nonlinear third harmonic crystal 15; a small part of the fundamental laser beam is converted into a horizontally polarized second harmonic beam by the type I nonlinear second harmonic crystal 14 through satisfying its phase matching condition (K (2W) ═ K (W) + K (W)) or non-critical phase matching (temperature tuning), the fundamental laser beam and the second harmonic beam are both transmitted toward the beam highly reflecting mirror 13 and reflected from the same mirror, when the fundamental laser beam passes through the type I nonlinear second harmonic crystal 14 upon reflection from the beam highly reflecting mirror 13, another small part of the fundamental laser beam is converted into its second harmonic beam which is superimposed with the reflected second harmonic beam to form a combined second harmonic beam, the type II nonlinear third harmonic crystal 15 satisfies the phase matching condition K (3W) ═ K (3W) —1/2(K (W) + K (2W)), a portion of the fundamental laser beam and most of the second harmonic beam delivered from the type I nonlinear second harmonic crystal 14 are converted into a third harmonic beam, fundamentalthe frequency laser beam, the second harmonic beam, the third harmonic beam enter prism two 17 where the beams are shifted from one to the other, the shifted beams enter prism one 16 increasing the displacement between the beams, the frequency laser beam leaving prism one 16 is directed to adjustable mirror 3 and reflected back to laser medium 6, the directing mirror 18 reflects the third and second harmonic beams and reflects the beams out of optical cavity 1, and the second harmonic emitter 19 blocks the second harmonic beam from the output.
The third harmonic enhanced reflection device 5 comprises a light beam high reflection lens 13, an I-type nonlinear second harmonic crystal 14, an II-type nonlinear third harmonic crystal 15 and a wave plate 20, wherein the light beam high reflection lens 13, the I-type nonlinear second harmonic crystal 14, the II-type nonlinear third harmonic crystal 15 and the wave plate 20 are sequentially arranged along the horizontal direction, the horizontal central axes of the light beam high reflection lens 13, the I-type nonlinear second harmonic crystal 14, the II-type nonlinear third harmonic crystal 15 and the wave plate 20 are arranged on the same horizontal common axis II, and the wave plate 20 is arranged between the II-type nonlinear third harmonic crystal 15 and the multi-wave high reflection lens 12.
Step 5) if the polarization of the third harmonic beam with the multi-wave high reflection mirror 12 is "P" polarization, then an improved recovery of the third harmonic beam from the laser cavity can be obtained, the fundamental laser beam is vertically reflected by the adjustable mirror 3 under vertical polarization, then the fundamental laser beam is reflected by the multi-wave high reflection mirror 12 and passes through the wave plate 20, the wave plate 20 rotates the fundamental laser beam to an integer of full wave or whole wave, the polarization of the fundamental laser beam is unchanged, the fundamental laser beam passes through the type II nonlinear third harmonic crystal 15, without the second harmonic beam, a part of the fundamental laser beam on the type I nonlinear second harmonic crystal 14 is converted to the second harmonic, the polarization of the fundamental laser beam remains vertical polarization, and the obtained second harmonic beam is horizontally polarized, the beam high reflection mirror 13 reflects the fundamental and second harmonic through the type I nonlinear second harmonic crystal 14, a further portion of the fundamental laser beam is converted to a horizontally polarized second harmonic, the fundamental laser beam and the second harmonic are directed through a type II nonlinear third harmonic crystal 15, which requires the fundamental laser beam and the second harmonic beam to occur in orthogonal polarizations on the crystal, a portion of the fundamental laser beam and a major portion of the second harmonic are converted to a third harmonic beam having the same polarization as the fundamental laser beam, in this case vertical polarization, the beam exiting the type II nonlinear third harmonic crystal 15 is directed through a waveplate 20, the waveplate 20 performs a 1/2 wave rotation on the third harmonic beam to convert its polarization to horizontal polarization before an incident occurs on its multi-wave highly reflective mirror 12, which will remove substantially all of the third harmonic beam from the laser cavity.
The third harmonic enhanced reflection device 5 comprises a light beam high reflection lens 13, an I-type doubling crystal 2, an I-type frequency tripling crystal 21 and a wave plate 20, wherein the light beam high reflection lens 13, the I-type doubling crystal 2, the wave plate 20 and the I-type frequency tripling crystal 21 are sequentially arranged along the horizontal direction, the horizontal central axes of the light beam high reflection lens 13, the I-type doubling crystal 2, the wave plate 20 and the I-type frequency tripling crystal 21 are arranged on the same horizontal common axis II, and the wave plate 20 is arranged between the I-type frequency tripling crystal 21 and the I-type frequency tripling crystal 2.
Step 5) the fundamental laser beam with vertical polarization is reflected by the adjustable mirror 3 to the multiple wave high reflection mirror 12, reflected by the I-type frequency tripling crystal 21 and the wave plate 20, the fundamental laser beam is not affected when passing through the I-type frequency tripling crystal 21, the crystal has no effect on the fundamental laser beam unless the second harmonic beam is polarized in parallel with the fundamental laser beam, the polarization of the fundamental laser beam is unchanged by the wave plate 20, the beam is generated on the I-type frequency doubling crystal 2, the I-type frequency doubling crystal 2 converts a part of the fundamental laser beam into a horizontally polarized second harmonic beam, the fundamental laser beam and the second harmonic are reflected from the beam high reflection mirror 13 back to the I-type frequency doubling crystal 2, wherein a part of the fundamental laser beam is converted again into a horizontally polarized second harmonic beam, the polarization of the second harmonic beam is rotated by one half wave when passing through the wave plate 20, the fundamental and second harmonic beams have polarization, this is necessary for the type I triple crystal used for the third harmonic conversion, a part of the fundamental laser beam and most of the second harmonic are converted into a third harmonic beam and exit the type I triple frequency crystal 21, the generated third harmonic will be horizontally polarized, and then the horizontally polarized third harmonic is incident on the multi-wave highly reflective mirror 12, the orientation of the multi-wave highly reflective mirror 12 is such that the horizontally polarized beam will be P-polarized to the multi-wave highly reflective mirror 12, the P-polarized third harmonic will be substantially completely transmitted through the multi-wave highly reflective mirror 12, and since the multi-wave highly reflective mirror 12 is reflective to the fundamental laser beam, the unconverted fundamental beam will be reflected.
an optical resonant cavity is formed between the first fundamental frequency high reflection mirror 8 and the beam high reflection mirror 13, the adjustable mirror 3 can adjust the angle of the adjustable mirror 3, the adjustable mirror 3 is a folding mirror, the laser medium 6 can be preselected, the cylindrical lens 11 has the thermal lens characteristic of a compensation crystal, the spherical lens 10 is used for adjusting the spot size of the beam, the first fundamental frequency high reflection mirror 8 is a high reflection mirror of the fundamental frequency of the laser medium 6, the type I nonlinear second harmonic crystal 14 is used for generating the second harmonic, the type II nonlinear third harmonic crystal 15 is used for generating the third harmonic, the beam high reflection mirror 13 is a high reflection mirror of the fundamental frequency and the second harmonic frequency spectrum, the first high reflection mirror and the beam high reflection mirror 13 define the optical cavity 1, the multi-wave high reflection mirror 12 is a dichroic mirror, the type I nonlinear second harmonic crystal 14 is a type I LBO crystal, the II-type nonlinear third harmonic crystal 15 is a II-type lithium triborate crystal.
The first prism 16 and the second prism 17 are fused siliconized prisms 16 and 17 with UV gradual change.
In particular use, the laser medium 6 is used for generating a fundamental frequency laser beam which is transmitted backwards along a common axis towards the front end and the back end, the laser pump 7 is used for exciting the laser medium 6, the fundamental frequency laser beam is transmitted forwards to the spherical lens 10 and continues to reach the cylindrical lens 11 and the Q-switch 9, the spherical lens 10 adjusts the spot size of the beam, the cylindrical lens 11 compensates the thermal lens characteristic of the crystal, in the Q-switch 9 option, the laser is inhibited by introducing loss in the resonant cavity, the energy pump is pumped and stored in population inversion, once the required population inversion is obtained, the loss is reduced to allow the laser to be transmitted, in this mode, a large pulse train output can be generated from the laser, and the fundamental frequency laser beam is transmitted backwardsThe laser beam reaches the adjustable reflector 3, the adjustable reflector 3 reflects a part of fundamental frequency laser beam to the fundamental frequency high reflector I8 along the common axis I and then reaches the original fundamental frequency laser beam of the fundamental frequency high reflector I8, the fundamental frequency high reflector I8 reflects the laser beam, the fundamental frequency laser beam reaches the adjustable reflector 3, and the adjustable reflector 3 oscillates with the optical output of the front end fundamental frequency high reflector I8 from the laser medium 6; the inclination angle of the reflector 3 can be adjusted manually to make the reflector vertically reflect the fundamental frequency laser beam or obliquely reflect the fundamental frequency laser beam; the fundamental frequency laser beam is vertically reflected by the adjustable reflector 3 to reach the multi-wave high-reflection mirror 12, and the multi-wave high-reflection mirror 12 reflects the fundamental frequency laser beam so that the fundamental frequency laser beam is transmitted forwards along the second common axis; the reflected fundamental laser beam passing through the multiple wave high reflection mirror 12 reaches the II type nonlinear third harmonic crystal 15, the II type nonlinear third harmonic crystal 15 oscillates with the light beam reflected by the multiple wave high reflection mirror 12, the output of the II type nonlinear third harmonic crystal 15 points to the I type nonlinear second harmonic crystal 14 for the generation of the second harmonic, the output of the I type nonlinear second harmonic crystal 14 points to the light beam high reflection mirror 13, because the II type nonlinear third harmonic crystal 15 converts the fundamental light beam into the third harmonic light beam only under the condition that the second harmonic light beam exists, the fundamental laser beam is not affected when passing through the II type nonlinear third harmonic crystal 15; a small part of the fundamental laser beam is converted into a horizontally polarized second harmonic beam by the type I nonlinear second harmonic crystal 14 through satisfying its phase matching condition (K (2W) ═ K (W) + K (W)) or non-critical phase matching (temperature tuning), the fundamental laser beam and the second harmonic beam are both transmitted toward the beam highly reflecting mirror 13 and reflected from the same mirror, when the fundamental laser beam passes through the type I nonlinear second harmonic crystal 14 upon reflection from the beam highly reflecting mirror 13, another small part of the fundamental laser beam is converted into its second harmonic beam which is superimposed with the reflected second harmonic beam to form a combined second harmonic beam, the type II nonlinear third harmonic crystal 15 satisfies the phase matching condition K (3W) ═ K (3W) —1/2(K (W) + K (2W)), a part of the fundamental laser beam is combined with the second harmonic nonlinear crystal of type I14 converting a majority of the second harmonic beam transmitted into a third harmonic beam; the fundamental frequency laser beam, the second harmonic beam and the third harmonic beam are directed to the multiple wave high reflection mirror 12, the multiple wave high reflection mirror 12 removes the third harmonic beam from the cavity, reflects the second harmonic beam to the adjustable reflection mirror 3, and can be output from the optical cavity 1 together as the second harmonic beam and the third harmonic beam; the fundamental laser beam is obliquely reflected by the adjustable reflector 3 to reach a first prism 16 and a second prism 17, the first prism 16 and the second prism 17 deflect the fundamental beam and guide the fundamental beam to a second-type nonlinear third harmonic crystal 15, the first prism 16 and the second prism 17 deflect the fundamental beam and guide the fundamental beam to the second-type nonlinear third harmonic crystal 15, the second-type nonlinear third harmonic crystal 15 outputs and directs to a first-type nonlinear second harmonic crystal 14 for second harmonic generation, the first-type nonlinear second harmonic crystal 14 outputs and directs to a beam highly-reflecting mirror 13, and since the second-type nonlinear third harmonic crystal 15 converts the fundamental beam into a third harmonic beam only in the presence of the second harmonic beam, the fundamental laser beam is not affected when passing through the second-type nonlinear third harmonic crystal 15; a small part of the fundamental laser beam is converted into a horizontally polarized second harmonic beam by the type I nonlinear second harmonic crystal 14 through satisfying its phase matching condition (K (2W) ═ K (W) + K (W)) or non-critical phase matching (temperature tuning), the fundamental laser beam and the second harmonic beam are both transmitted toward the beam highly reflecting mirror 13 and reflected from the same mirror, when the fundamental laser beam passes through the type I nonlinear second harmonic crystal 14 upon reflection from the beam highly reflecting mirror 13, another small part of the fundamental laser beam is converted into its second harmonic beam which is superimposed with the reflected second harmonic beam to form a combined second harmonic beam, the type II nonlinear third harmonic crystal 15 satisfies the phase matching condition K (3W) ═ K (3W) —1/2(K (W) + K (2W)) converting a portion of the fundamental laser beam and most of the second harmonic beam delivered from the type I nonlinear second harmonic crystal 14 into third harmonic beam, the fundamental laser beam, the second harmonic beam, the third harmonic beam enter prism two 17 where the beams are shifted from one to another, the shifted beams enter prism one 16, increasing the number of beams between themThe fundamental laser beam leaving the first prism 16 is directed to the adjustable mirror 3 and reflected back to the laser medium 6, the directing mirror 18 reflects the third and second harmonic beams and reflects the beams out of the optical cavity 1, and the second harmonic emitter 19 blocks the second harmonic beam from the output; if the polarization of the third harmonic beam with the multi-wave high reflection optic 12 is "P" polarization, improved recovery of the third harmonic beam from the laser cavity can be achieved, achieving removal of more than about 90%, preferably about 95% to 99%, more preferably about 99% of the third harmonic, the fundamental laser beam being reflected vertically with vertical polarization by the adjustable mirror 3, then the fundamental laser beam being reflected by the multi-wave high reflection optic 12 and passing through the waveplate 20, which is better than 99.5% reflected under the fundamental laser beam, and better than 95% transmitted at the third harmonic beam when the third harmonic beam occurs on the optic at P-polarization to the optic, the waveplate 20 rotating the fundamental laser beam to a full wave or integer of a whole wave, the polarization of the fundamental laser beam being unchanged, the fundamental laser beam passing through the type II nonlinear third harmonic crystal 15, unaffected without the second harmonic beam, a part of the fundamental laser beam is converted into a second harmonic on the type I nonlinear second harmonic crystal 14, the polarization of the fundamental laser beam is kept vertically polarized, and the resultant second harmonic beam is horizontally polarized, the beam highly reflecting mirror 13 reflects the fundamental wave and the second harmonic by the type I nonlinear second harmonic crystal 14, and a further part of the fundamental laser beam is converted into a horizontally polarized second harmonic, and the fundamental laser beam and the second harmonic are guided through the type II nonlinear third harmonic crystal 15, which requires the fundamental laser beam and the second harmonic beam to occur on the crystal in polarization orthogonal to each other, a part of the fundamental laser beam and a major part of the second harmonic are converted into a third harmonic beam having the same polarization as that of the fundamental laser beam, in this case, vertically polarized, and the beam leaving the type II nonlinear third harmonic crystal 15 is guided through the wave plate 20, the wave plate 20 performs a 1/2 wave rotation on the third harmonic beam to convert its polarization to horizontal before an accident occurs on its multi-wave high mirror 12, which multi-wave high mirror 12 will remove substantially all the third harmonic beam from the laser cavity; with vertical offsetThe oscillating fundamental laser beam is reflected by the adjustable mirror 3 to the multiple-wave high-reflection mirror 12, reflected by the I-type frequency tripling crystal 21 and the wave plate 20, the fundamental laser beam is not affected when passing through the I-type frequency tripling crystal 21, the crystal has no effect on the fundamental beam unless the second harmonic beam is polarized in parallel with the fundamental laser beam, the polarization of the fundamental laser beam is unchanged by the wave plate 20, the beam is generated on the I-type frequency doubling crystal 2, the I-type frequency doubling crystal 2 converts a part of the fundamental laser beam into a horizontally polarized second harmonic beam, the fundamental laser beam and the second harmonic are reflected from the beam high-reflection mirror 13 back to the I-type frequency doubling crystal 2, wherein a part of the fundamental laser beam is converted into a horizontally polarized second harmonic beam again, the polarization of the second harmonic beam is rotated by one half wave when passing through the wave plate 20, and the fundamental and second harmonic, this is necessary for the type I triple crystal used for the third harmonic conversion, a part of the fundamental laser beam and most of the second harmonic are converted into a third harmonic beam and exit the type I triple frequency crystal 21, the generated third harmonic will be horizontally polarized, and then the horizontally polarized third harmonic is incident on the multi-wave highly reflective mirror 12, the orientation of the multi-wave highly reflective mirror 12 is such that the horizontally polarized beam will be P-polarized to the multi-wave highly reflective mirror 12, the P-polarized third harmonic will be substantially completely transmitted through the multi-wave highly reflective mirror 12, and since the multi-wave highly reflective mirror 12 is reflective to the fundamental laser beam, the unconverted fundamental beam will be reflected.
the present invention and its embodiments have been described above, and the description is not intended to be limiting, and the drawings are only one embodiment of the present invention, and the actual structure is not limited thereto. In summary, those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for carrying out the same purposes of the present invention without departing from the spirit and scope of the invention as defined by the appended claims.