阅读说明：本技术 产生周期连续可调激光阵列线源的光学系统及其调节方法 (Optical system for generating laser array line source with continuously adjustable period and adjusting method thereof ) 是由 姚东 岳猛猛 尹飞 王迪 吴永程 刘冲 李知兵 张�杰 李亚晖 温珂瑶 高贵龙 于 2021-09-18 设计创作，主要内容包括：本发明涉及一种产生周期连续可调激光阵列线源的光学系统及其调节方法,可用作激光超声无损检测的激励源。克服现有激光阵列线源,周期无法连续可调的问题。光学系统包括脉冲激光器、分束镜、光学延迟线、可调反射镜及合束镜；分束镜将脉冲激光分为透射光束与反射光束；光学延迟线将反射光束和透射光束之间的相对光程差调节为零；可调反射镜调节反射光束与透射光束之间的夹角；合束镜将经过光学延迟线以及可调反射镜的反射光束及透射光束合束,反射光束及透射光束发生干涉,干涉条纹即为输出的激光阵列线源,利用可调反射镜调节反射光束与透射光束之间的夹角,实现激光阵列线源周期连续调整。(The invention relates to an optical system for generating a laser array line source with continuously adjustable period and an adjusting method thereof, which can be used as an excitation source for laser ultrasonic nondestructive testing. The problem that the period of the existing laser array line source cannot be continuously adjusted is solved. The optical system comprises a pulse laser, a beam splitter, an optical delay line, an adjustable reflector and a beam combiner; the beam splitter divides the pulse laser into a transmission beam and a reflection beam; the optical delay line adjusts the relative optical path difference between the reflected beam and the transmitted beam to zero; the adjustable reflector adjusts an included angle between the reflected light beam and the transmitted light beam; the beam combining mirror combines the reflected light beam and the transmitted light beam which pass through the optical delay line and the adjustable reflector, the reflected light beam and the transmitted light beam interfere, the interference fringe is the output laser array line source, and the adjustable reflector is utilized to adjust the included angle between the reflected light beam and the transmitted light beam, so that the periodic continuous adjustment of the laser array line source is realized.)

1. An optical system for generating a laser array line source with continuously adjustable period comprises a pulse laser, and is characterized by further comprising a beam splitter, an optical delay line, an adjustable reflector and a beam combiner;

the beam splitter is arranged in an emergent light path of the pulse laser and is used for splitting the pulse laser into a transmission beam and a reflection beam;

the optical delay line is arranged in a transmission light path or a reflection light path of the beam splitter and is used for adjusting the relative optical path difference between the reflected light beam and the transmitted light beam to be zero;

the adjustable reflector is arranged in a transmission light path or a reflection light path of the beam splitter and is used for adjusting an included angle between a reflected beam and a transmitted beam;

the beam combining mirror is arranged in a transmission light path and a reflection light path of the beam splitting mirror, and is used for combining a reflected beam and a transmitted beam which pass through the optical delay line and the adjustable reflecting mirror, the reflected beam and the transmitted beam interfere, interference fringes are output laser array line sources, and the adjustable reflecting mirror is used for adjusting an included angle between the reflected beam and the transmitted beam, so that the period continuous adjustment of the laser array line sources is realized.

2. The optical system for generating a periodically continuously tunable laser array line source of claim 1, wherein: the light attenuator is arranged in the transmission light path or the reflection light path of the beam splitter and used for adjusting the light intensity of the transmission light beam or the reflection light beam so that the light intensity of the two beams after passing through the beam combiner is equal.

3. The optical system for generating a periodically continuously tunable laser array line source of claim 2, wherein: the beam combiner also comprises a reflecting mirror component arranged in the transmission light path and/or the reflection light path of the beam splitter and used for adjusting the propagation direction of the transmission light beam and/or the reflection light beam and finally ensuring that the transmission light beam and the reflection light beam are converged at the beam combiner.

4. The optical system for generating a periodically continuously tunable laser array line source of claim 3, wherein: the laser beam splitter also comprises a wave front shaping device which is used for carrying out wave front shaping on the pulse laser, gating the central light spot with more uniform light intensity, and leading the central light spot to enter the beam splitter after beam expanding and collimating.

5. The optical system for generating a periodically continuously tunable laser array line source of claim 4, wherein: the adjustable reflector is controlled by a piezoelectric precise driving controller to realize small-angle rotation.

6. The optical system for generating a periodically continuously tunable laser array line source of claim 5, wherein: the transmission to reflection ratio of the beam splitter is 50: 50.

7. The optical system for generating a periodically continuously tunable laser array line source of claim 6, wherein: the transmission and reflection ratio of the beam combining mirror is 50: 50.

8. The optical system for generating a periodically continuously tunable laser array line source of claim 7, wherein: the pulse laser is nanosecond, picosecond or modulatable pulse laser, and the pulse laser is distributed in a Laguerre-Gaussian or Hermite-Gaussian manner.

9. The optical system for generating a periodically continuously tunable laser array line source of claim 8, wherein: the optical delay line is arranged in a transmission light path of the beam splitter, and the adjustable reflector is arranged in a reflection light path of the beam splitter; the optical attenuator is arranged in a reflection light path of the adjustable reflector.

10. The optical system for generating a periodically continuously tunable laser array line source of claim 9, wherein: the reflector component comprises a first reflector, a second reflector and a third reflector; the first reflecting mirror and the second reflecting mirror are vertical to each other, are sequentially arranged in a reflecting light path of the beam splitter and reflect a reflecting beam to the adjustable reflecting mirror; the third reflector is arranged in a transmission light path of the beam splitter and reflects the transmission light beam to the beam combiner.

11. A method of adjusting an optical system for generating a periodically continuously tunable laser array line source as claimed in claim 1, comprising the steps of:

step 1, starting a system;

starting a pulse laser, dividing pulse light emitted by the pulse laser into two parts through a beam splitter, enabling a transmission light beam to enter a beam combiner through an optical delay line, and combining the transmission light beam and a reflection light beam passing through an adjustable reflector through the beam combiner; or the transmitted light beam is incident on the beam combining mirror through the optical delay line and the adjustable reflecting mirror, and is combined with the reflected light beam of the beam splitting mirror in the beam combining mirror; or the transmission light beam is incident on the beam combining mirror through the adjustable reflecting mirror and is combined with the reflected light beam passing through the optical delay line through the beam combining mirror; the reflected light beam is incident on the beam combining mirror through the optical delay line and the adjustable reflecting mirror, and is combined with the transmitted light beam of the beam splitting mirror in the beam combining mirror;

step 2, adjusting optical path difference;

adjusting the relative optical path difference between the reflected beam and the transmitted beam to be zero by using an optical delay line, wherein the bright and dark stripes output by the beam combiner are laser array line sources;

step 3, adjusting the period of the laser array line source;

adjusting the horizontal steering of the adjustable reflector to enable an included angle between a reflected beam and a transmitted beam after passing through the beam combiner to be alpha, and according to the equal-thickness interference principle, the interval between adjacent bright stripes, namely the period of a laser array line source is as follows:

wherein n is the refractive index of air, and λ is the wavelength;

and continuously adjusting the horizontal steering of the adjustable reflector to obtain laser interference fringes at different intervals, thereby realizing the continuous adjustment of the line source period of the laser array.

12. The adjustment method according to claim 11, characterized in that step 1 is specifically:

and starting the pulse laser, dividing pulse light emitted by the pulse laser into two parts through the beam splitter, enabling the transmitted light beam to enter the third reflector through the optical delay line, then reflecting the transmitted light beam to the beam combiner through the third reflector, and combining the transmitted light beam and a reflected light beam passing through the first reflector, the second reflector, the adjustable reflector and the optical attenuator in sequence through the beam combiner.

Technical Field

The invention relates to an optical system for generating a laser array line source with continuously adjustable period and an adjusting method thereof, which can be used as an excitation source for laser ultrasonic nondestructive testing.

Background

Laser ultrasound is a non-contact, non-destructive inspection technique that utilizes laser excitation and laser reception of ultrasonic waves. The basic working principle is that a beam of pulse laser is incident to the surface of a material, part of laser energy is absorbed by the material and converted into heat energy, the local rapid temperature rise of a laser irradiation area leads to local rapid thermal expansion to generate ultrasonic waves, and then an optical receiving device collects and demodulates ultrasonic signals. The ultrasonic wave in the laser ultrasonic detection is generated by the laser thermo-elastic effect, a coupling agent is not needed, and the detected piece does not need to be in contact with a detection instrument, so that non-contact and remote detection can be realized; the laser-excited ultrasonic wave has wider frequency band, high detection resolution and wide application occasions; the all-optical excitation and detection can realize real-time online detection of the to-be-detected piece in extreme environments such as high temperature, high pressure, corrosion, strong radiation and the like; and support the quick large tracts of land scanning of test piece and detect, be convenient for form images.

Traditional laser ultrasound uses laser point source or single line source laser to generate ultrasound, and ultrasonic signals excited by the point source or single line source laser are weak and have poor signal-to-noise ratio. In addition, the laser array line source is adopted to excite the ultrasound, the laser array line source can input more energy on the premise of not damaging the surface, the intensity of the excited ultrasonic wave is improved, the frequency spectrum amplitude of the excited surface acoustic wave can be improved by regulating and optimizing parameters such as the line source width, the line source period and the like of the array line source, and the sensitivity and the signal-to-noise ratio of the laser ultrasonic detection system are improved. The traditional laser array line source is mainly generated by using methods such as a surface mask, a lens array, an optical fiber array and the like, and the period of the array line source cannot be continuously adjusted. One mask or one lens (optical fiber) array can only generate an array line source with a fixed period, and if the period of the array line source needs to be adjusted, different masks or lens (optical fiber) arrays need to be replaced, so that the system is complex, expensive and poor in flexibility.

Disclosure of Invention

The invention aims to provide an optical system for generating a laser array line source with continuously adjustable period, which solves the problem that the period of the existing laser array line source cannot be continuously adjustable. The optical system of the invention can realize the continuous adjustment of the laser array line source period from millimeter to micron without replacing optical elements, can input more laser energy under the condition of not damaging the surface of a material, increases the excitation source intensity and the regulation and control flexibility of the laser ultrasonic nondestructive detection system, and is beneficial to improving the detection sensitivity and the signal to noise ratio.

The technical scheme of the invention provides an optical system for generating a periodic continuous adjustable laser array line source, which comprises a pulse laser, and is characterized by further comprising a beam splitter, an optical delay line, an adjustable reflector and a beam combiner;

the beam splitter is arranged in an emergent light path of the pulse laser and is used for splitting the pulse laser into a transmission beam and a reflection beam;

the optical delay line is arranged in a transmission light path or a reflection light path of the beam splitter and is used for adjusting the relative optical path difference between the reflected light beam and the transmitted light beam to be zero;

the adjustable reflector is arranged in a transmission light path or a reflection light path of the beam splitter and is used for adjusting an included angle between a reflected beam and a transmitted beam;

the beam combining mirror is arranged in a transmission light path and a reflection light path of the beam splitting mirror, and is used for combining a reflected beam and a transmitted beam which pass through the optical delay line and the adjustable reflecting mirror, the reflected beam and the transmitted beam interfere, interference fringes are output laser array line sources, and the adjustable reflecting mirror is used for adjusting an included angle between the reflected beam and the transmitted beam to realize the periodic continuous adjustment of the laser array line sources.

Further, the optical system may further include an optical attenuator disposed in the transmission optical path or the reflection optical path of the beam splitter, and configured to adjust the light intensity of the transmission light beam or the reflection light beam, so that the light intensities of the two beams passing through the beam combiner are equal.

Furthermore, the optical system also comprises a reflecting mirror component arranged in the transmission light path and/or the reflection light path of the beam splitter and used for adjusting the propagation direction of the transmission light beam and/or the reflection light beam and finally ensuring that the transmission light beam and the reflection light beam are converged at the beam combiner.

Furthermore, in order to improve the uniformity of the laser array line source which finally emits, the system also comprises a wave front shaping device which is used for carrying out wave front shaping on the pulse laser, gating the central light spot with more uniform light intensity, and leading the central light spot to enter the beam splitter after beam expanding and collimating.

Furthermore, in order to accurately control the rotation angle of the adjustable mirror, the system can further comprise a piezoelectric precision driving controller which controls the adjustable mirror to realize small-angle rotation.

Further, the transmission-to-reflection ratio of the beam splitter is 50: 50.

Further, the transmission-to-reflection ratio of the beam combiner is 50: 50.

Further, the pulse laser is a nanosecond, picosecond or modulatable pulse laser, and the pulse laser is distributed in a Laguerre-Gaussian or Hermite-Gaussian distribution.

Further, the optical delay line is disposed in a transmission optical path of the beam splitter, and the adjustable mirror is disposed in a reflection optical path of the beam splitter.

Further, the optical attenuator is arranged in a reflection light path of the adjustable reflecting mirror.

Further, the mirror assembly includes a first mirror, a second mirror, and a third mirror; the reflecting surfaces of the first reflecting mirror and the second reflecting mirror are mutually vertical, are sequentially arranged in the reflecting light path of the beam splitter and reflect the reflected light beam to the adjustable reflecting mirror; the third reflector is arranged in a transmission light path of the beam splitter and reflects the transmission light beam to the beam combiner.

The invention also provides an adjusting method of the optical system for generating the laser array line source with the continuously adjustable period, which is characterized by comprising the following steps of:

step 1, starting a system;

starting a pulse laser, dividing pulse light emitted by the pulse laser into two parts through a beam splitter, enabling a transmission light beam to enter a beam combiner through an optical delay line, and combining the transmission light beam and a reflection light beam passing through an adjustable reflector through the beam combiner; or the transmitted light beam is incident on the beam combining mirror through the optical delay line and the adjustable reflecting mirror, and is combined with the reflected light beam of the beam splitting mirror in the beam combining mirror; or the transmission light beam is incident on the beam combining mirror through the adjustable reflecting mirror and is combined with the reflected light beam passing through the optical delay line through the beam combining mirror; the reflected light beam is incident on the beam combining mirror through the optical delay line and the adjustable reflecting mirror, and is combined with the transmitted light beam of the beam splitting mirror in the beam combining mirror;

step 2, adjusting optical path difference;

adjusting the relative optical path difference between the reflected beam and the transmitted beam to be zero by using an optical delay line, wherein the bright and dark stripes output by the beam combiner are laser array line sources;

step 3, adjusting the period of the laser array line source;

adjusting the horizontal steering of the adjustable reflector to enable an included angle between a reflected beam and a transmitted beam after passing through the beam combiner to be alpha, and according to the equal-thickness interference principle, the interval between adjacent bright stripes, namely the period of a laser array line source is as follows:

wherein n is the refractive index of air, and λ is the wavelength;

and continuously adjusting the horizontal steering of the adjustable reflector to obtain laser interference fringes at different intervals, thereby realizing the continuous adjustment of the line source period of the laser array.

Further, step 1 specifically comprises:

and starting the pulse laser, dividing pulse light emitted by the pulse laser into two parts through the beam splitter, enabling the transmitted light beam to enter the third reflector through the optical delay line, then reflecting the transmitted light beam to the beam combiner through the third reflector, and combining the transmitted light beam and a reflected light beam passing through the first reflector, the second reflector, the adjustable reflector and the optical attenuator in sequence through the beam combiner.

The invention has the beneficial effects that:

1. the optical system for generating the laser array line source with the continuously adjustable period is based on the principle of double-beam interference, and the continuous adjustment of the period of two beams of light interference fringes (the laser array line source) is realized by adjusting the horizontal included angle of the two beams of light through adjusting the rotation angle of the adjustable reflecting mirror. Can be applied to the fields of laser ultrasonic nondestructive testing and the like.

2. The optical system for generating the laser array line source with the continuously adjustable period, provided by the invention, does not need to continuously replace a mask or a lens (optical fiber) array, is simple to operate, is easy to realize and has high flexibility.

3. The optical system for generating the laser array line source with the continuously adjustable period, provided by the invention, has the advantages of low cost, compact structure and easiness in integration, and is beneficial to miniaturization of equipment.

Drawings

FIG. 1 is a schematic diagram of an optical system in accordance with one embodiment of the present invention;

the reference numbers in the figures are: the laser comprises a pulse laser 1, a beam splitter 2, an optical delay line 3, a third reflector 4, a first reflector 5, a second reflector 6, an adjustable reflector 7, an optical attenuator 8 and a beam combiner 9.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, specific embodiments accompanied with figures are described in detail below, and it is apparent that the described embodiments are a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making creative efforts based on the embodiments of the present invention, shall fall within the protection scope of the present invention.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

Furthermore, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.

The invention relates to an optical system for generating a periodic continuous adjustable laser array line source, which mainly comprises a pulse laser, a beam splitter, an optical delay line, an adjustable reflector and a beam combiner;

the pulse laser is a laser ultrasonic excitation light source and is a nanosecond, picosecond or modulated pulse laser. The beam splitter is designed for an incident light waveband, and has a transmission and reflection ratio of 50: and 50, arranged in the emergent light path of the pulse laser, for dividing the pulse laser into a transmitted beam and a reflected beam. The optical delay line is arranged in a transmission light path or a reflection light path of the beam splitter and is used for adjusting the optical path difference of the two paths of light. The adjustable reflector is arranged in a transmission light path or a reflection light path of the beam splitter and used for accurately adjusting an included angle between two beams of light after passing through the beam combiner. The beam combiner is used for combining two reflected beams of light and two transmitted beams of light into one, and the transmission and reflection ratio is 50: 50. after the beam is closed, the reflected beam and the transmitted beam interfere with each other, the interference fringe is the output laser array line source, and the adjustable reflector is used for adjusting the included angle between the reflected beam and the transmitted beam, so that the periodic continuous adjustment of the laser array line source is realized. The optical attenuator can be arranged in a transmission light path or a reflection light path of the beam splitter and used for adjusting the light intensity of the transmission light beam or the reflection light beam, so that the light intensity of the two beams after passing through the beam combiner is equal, and the interference contrast is improved. The device also comprises a reflecting mirror component which is arranged in the transmission light path and/or the reflection light path of the beam splitter and is used for adjusting the propagation direction of the transmission light beam and/or the reflection light beam and finally ensuring that the transmission light beam and the reflection light beam are converged at the beam combiner.

Example 1

As can be seen from fig. 1, the optical system for generating the periodic continuous tunable laser array line source in this embodiment includes a pulse laser 1, a beam splitter 2 disposed in the emergent light path of the pulse laser 1, a first mirror 5, a second mirror 6, a tunable mirror 7, an optical attenuator 8 sequentially disposed in the reflective light path of the beam splitter 2, an optical delay line 3 and a third mirror 4 sequentially disposed in the transmissive light path of the beam splitter 2, and a beam combiner 9 disposed in the emergent light path of the optical attenuator 8 and the third mirror 4. Of course, in other embodiments, the adjustable mirror 7 may be disposed in the transmission optical path of the beam splitter 2 simultaneously with the optical delay line 3, may also be disposed in the reflection optical path of the beam splitter 2 simultaneously, and may also be the adjustable mirror 7 disposed in the transmission optical path of the beam splitter 2, and the optical delay line 3 disposed in the reflection optical path of the beam splitter 2. The optical attenuator 8 may also be located in the transmission optical path of the beam splitter 2.

The working principle of the optical system of the embodiment is as follows: the pulse light emitted by the pulse laser 1 is divided into two parts by the beam splitter 2, and the reflection and transmission ratio of the beam splitter 2 is 50: and 50, the transmitted light beam and the reflected light beam are equal in intensity, the transmitted light beam is incident on the beam combiner 9 through the optical delay line 3 and the third reflector 4, and is combined with the other path of reflected light beam which sequentially passes through the first reflector 5, the second reflector 6, the adjustable reflector 7 and the optical attenuator 8. The optical delay line 3 is used for adjusting the relative optical path difference between the reflected light beam and the transmitted light beam, when the relative optical path difference between the two light beams is zero, the reflected light beam and the transmitted light beam converged on the beam combiner 9 meet the interference condition to interfere, and the bright and dark fringes in the interference field are output laser array line sources. The period of the output laser array line source is fixed, the continuous adjustment of the period needs to be completed through the adjustable reflecting mirror 7 in the horizontal direction, the horizontal steering of the adjustable reflecting mirror 7 in the horizontal direction is adjusted to enable a reflected beam and a transmitted beam to form a small included angle alpha, and according to the equal-thickness interference principle, the interval (the period of the array line source) between adjacent bright fringes is as follows:

therefore, laser interference fringes with different intervals can be obtained by continuously rotating the horizontal direction adjustable reflecting mirror 7, and continuous adjustment of the period of the laser array line source is realized.

In other embodiments, if the adjustable mirror 7 and the optical delay line 3 are simultaneously disposed in the transmission optical path of the beam splitter 2, the pulse light emitted from the pulse laser 1 is split into two parts by the beam splitter 2, and the transmitted light beam enters the beam combiner 9 through the optical delay line 3 and the adjustable mirror 7, and is combined with another reflected light beam sequentially passing through the corresponding mirror and the optical attenuator 8. If the adjustable reflector 7 and the optical delay line 3 are arranged in the reflection light path of the beam splitter 2 at the same time, the reflected light beam is incident on the beam combiner 9 through the optical delay line 3, the adjustable reflector 7 and the optical attenuator 8, and is combined with the transmitted light beam passing through the corresponding reflector in the beam combiner 9; if the adjustable reflector 7 is arranged in the transmission light path of the beam splitter 2 and the optical delay line 3 is arranged in the reflection light path of the beam splitter 2, the transmission light beam is incident on the beam combiner 9 through the adjustable reflector 7, and is combined with the reflection light beam passing through the optical delay line 3, the corresponding reflector and the attenuator through the beam combiner 9.

Similarly, the relative optical path difference between the reflected light beam and the transmitted light beam is adjusted by the optical delay line 3, when the relative optical path difference between the two light beams is zero, the reflected light beam and the transmitted light beam converged on the beam combiner 9 meet the interference condition to interfere, and the bright and dark fringes in the interference field are output laser array line sources. The period of the output laser array line source is fixed, the continuous adjustment of the period needs to be completed through the adjustable reflecting mirror 7 in the horizontal direction, the horizontal steering of the adjustable reflecting mirror 7 in the horizontal direction is adjusted to enable a reflected beam and a transmitted beam to form a small included angle alpha, and according to the equal-thickness interference principle, the interval (the period of the array line source) between adjacent bright fringes is as follows:

therefore, laser interference fringes with different intervals can be obtained by continuously rotating the horizontal direction adjustable reflecting mirror 7, and continuous adjustment of the period of the laser array line source is realized.

The pulse laser 1 can select pulse lasers 1 with different wavelengths and different pulse widths according to requirements. The pulse laser source is mostly distributed in a Laguerre-Gaussian or Hermite-Gaussian manner, the center of a light spot is strong, the two sides of the light spot are weak, and in order to improve the uniformity of the laser array line source which finally emits, the pulse laser can be subjected to wave front shaping, for example, the central light spot with more uniform light intensity can be gated, and the central light spot is incident to the beam splitter 2 after being expanded and collimated. The rotation angle of the horizontal direction adjustable reflecting mirror 7 is small, and the piezoelectric precise driving controller can be used for adjusting in practical use.