阅读说明：本技术 一种输出双波长中红外的光参量振荡器 (Optical parametric oscillator for outputting dual-wavelength mid-infrared light ) 是由 李志永 胡列懋 谭荣清 刘松阳 宁方晋 于 2019-09-27 设计创作，主要内容包括：本发明提出了一种输出双波长中红外的光参量振荡器,试验步骤简单、效率高,并且试验误差低。本发明中双波长中红外光束的产生于两个非线性过程,且两个非线性频率变换过程之间耦合度较小,光参量振荡产生的阈值低,便于调节各个波长的功率占比。2次光参量振荡过程的泵浦光由同一半导体激光器产生,使得双波长中红外光束具有严格的共光轴特点,是一种优质的气体差分吸收探测和太赫兹产生的激光源。(The invention provides an optical parametric oscillator for outputting mid-infrared light with dual wavelengths, which has the advantages of simple test steps, high efficiency and low test error. The infrared light beams in the dual-wavelength system are generated in two nonlinear processes, the coupling degree between the two nonlinear frequency conversion processes is small, the threshold value generated by optical parametric oscillation is low, and the power ratio of each wavelength can be adjusted conveniently. The pumping light in the 2-time optical parametric oscillation process is generated by the same semiconductor laser, so that the infrared light beam in the dual-wavelength has the strict coaxial-axis characteristic, and the laser source is a high-quality laser source for gas differential absorption detection and terahertz generation.)

1. An optical parametric oscillator for outputting dual-wavelength mid-infrared light is characterized by comprising a high-reflection mirror (1), a semiconductor laser (2), an input mirror (3), a polarizing device (4), an alkali metal vapor chamber (5), a dichroic mirror (7), a neodymium-doped crystal (8), a four-color mirror (9), a nonlinear crystal (10), an output coupling mirror (13) and a stepping translation table (12);

the high-reflection mirror (1) is high-reflection for alkali metal laser, the output coupling mirror (13) is high-reflection for alkali metal laser and near-infrared laser, and the output coupling mirror partially transmits the mid-infrared laser;

the high reflection mirror (1) and the output coupling mirror (13) form an alkali metal laser resonant cavity to realize optical amplification on alkali metal laser;

the polarization device (4), the alkali metal vapor chamber (5), the dichroic mirror (7), the neodymium-doped crystal (8), the four-color mirror (9) and the nonlinear crystal (10) are sequentially positioned in the alkali metal laser resonant cavity along the light-emitting direction;

the semiconductor laser (2) is positioned outside the alkali metal laser resonant cavity, and output semiconductor laser enters the alkali metal vapor chamber (5) through the polarizing device (4) and is used for pumping alkali metal vapor; the polarization device (4) is used for enabling the alkali metal laser to be linearly polarized and enabling the semiconductor laser to be coupled with the alkali metal laser;

the dichroic mirror (7) is highly transparent to alkali metal laser and highly reflective to near-infrared laser; the neodymium-doped crystal (8) generates near-infrared laser after being pumped by alkali metal laser; the dichroic mirror (7) and the output coupling mirror (13) form a near-infrared laser resonant cavity to amplify the near-infrared laser; the dichroic mirror (9) is highly reflective to the mid-infrared laser, highly transparent to the alkali metal laser and the near-infrared laser, and forms a resonant cavity mirror of the optical parametric oscillator with the output coupling mirror (13);

the alkali metal laser and the near-infrared laser are emitted to the nonlinear crystal (10) to generate mid-infrared laser, and the mid-infrared laser is output through an output coupling mirror (13);

the stepping translation table (12) is used for placing the nonlinear crystal (10), and the light passing channel of the nonlinear crystal is adjusted through the stepping translation table (12) to realize the tuning of multi-wavelength intermediate infrared output.

2. The output dual wavelength mid-infrared optical parametric oscillator of claim 1, wherein the spacing of the dual wavelengths is adjusted by laterally shifting the nonlinear crystal.

3. The optical parametric oscillator for mid-infrared at output dual wavelengths according to claim 1, wherein the semiconductor laser is focused by an input mirror (3) and then enters an alkali metal vapor chamber (5) through a polarizer (4), and the input mirror (3) is a focusing mirror or an off-axis parabolic mirror.

4. The alkali metal laser difference frequency based mid-infrared laser according to claim 1, characterized in that the polarizing device (4) is a polarizing beam splitting cube or a glan laser prism.

5. Alkali laser difference frequency based mid-infrared laser according to claim 1, characterized in that the position of the alkali vapour chamber (5) and the polarizing device (4) is interchanged.

6. The alkali metal laser difference frequency-based mid-infrared laser according to claim 1, wherein the output coupling mirror (13) has an output coupling ratio for both the idler light and the signal light, and outputs the idler light and the signal light simultaneously.

7. The alkali metal laser difference frequency-based mid-infrared laser according to claim 1, wherein the output coupling mirror (13) has an output coupling ratio for each of the idler light, the signal light, and the alkali metal laser, and outputs the idler light, the signal light, and the alkali metal laser at the same time.

Technical Field

The invention belongs to the technical field of optical parametric oscillators, and particularly relates to an optical parametric oscillator for outputting dual-wavelength mid-infrared light.

Background

The penetration capacity of the 3-5 mu m intermediate infrared laser to smoke and atmosphere is strong, so that the laser in the waveband has a wide application prospect in the aspects of biomedicine, gas detection and the like. Compared with single-wavelength mid-infrared laser, the application of the dual-wavelength mid-infrared laser is more distinctive, terahertz wave generation can be realized through the dual-wavelength mid-infrared laser, and multi-component gas synchronous detection can also be realized.

The optical parametric oscillator is one of the main ways to obtain mid-infrared laser, has a wide wavelength tuning range, and can realize laser output in a wide range of wave bands through various ways (cycle tuning, wavelength tuning, temperature tuning and the like). For a nonlinear crystal with a certain polarization period, a nonlinear phenomenon is generated under the pumping of pumping light (wavelength lambda), and the generated wavelength is lambda_IIdler and wavelength of_SThe signal light of (1). The technical means can realize multi-wavelength intermediate infrared output by the aid of the technical means that multi-wavelength pump light simultaneously pumps a single-period nonlinear crystal and single-wavelength pump light pumps a cascaded double-period nonlinear crystal.

For the optical parametric oscillator of the cascade nonlinear crystal, the oscillation threshold value in the resonant cavity is higher, so that the requirement on the power of a pumping source is higher. In addition, when a laser with multi-wavelength output is used as a pumping source of the optical parametric oscillator, the cavity structure is complex, the optical path needs to be accurately controlled, the adjustment difficulty is high, and the conversion efficiency is influenced by the loss of pumping light in the resonant cavity.

Disclosure of Invention

In view of this, the invention provides an optical parametric oscillator outputting mid-infrared light with dual wavelengths, which has the advantages of simple test steps, high efficiency and low test error.

In order to achieve the purpose, the technical scheme of the invention is as follows:

the invention discloses an optical parametric oscillator for outputting dual-wavelength mid-infrared light, which comprises a high-reflection mirror, a semiconductor laser, an input mirror, a polarizing device, an alkali metal vapor chamber, a dichroic mirror, a neodymium-doped crystal, a dichroic mirror, a nonlinear crystal, an output coupling mirror and a stepping translation stage;

the high-reflection mirror is high-reflection to the alkali metal laser, the output coupling mirror is high-reflection to the alkali metal laser and the near-infrared laser, and the output coupling mirror is partially transparent to the mid-infrared laser;

the high-reflection mirror and the output coupling mirror form an alkali metal laser resonant cavity to realize optical amplification on the alkali metal laser;

the polarizing device, the alkali metal vapor chamber, the dichroic mirror, the neodymium-doped crystal, the four-color mirror and the nonlinear crystal are sequentially positioned in the alkali metal laser resonant cavity along the light emergent direction;

the semiconductor laser is positioned outside the alkali metal laser resonant cavity, and the output semiconductor laser enters the alkali metal vapor chamber through the polarizing device and is used for pumping the alkali metal vapor; the polarization device is used for enabling the alkali metal laser to be linearly polarized and enabling the semiconductor laser to be coupled with the alkali metal laser;

the dichroic mirror is highly transparent to alkali metal laser and highly reflective to near-infrared laser; the neodymium-doped crystal generates near-infrared laser after being pumped by alkali metal laser; the dichroic mirror and the output coupling mirror form a near-infrared laser resonant cavity to realize light amplification on the near-infrared laser; the four-color mirror is highly reflective to the mid-infrared laser, highly transparent to the alkali metal laser and the near-infrared laser, and forms a resonant cavity mirror of the optical parametric oscillator with the output coupling mirror;

the alkali metal laser and the near-infrared laser are emitted to the nonlinear crystal to generate mid-infrared laser, and the mid-infrared laser is output through the output coupling mirror;

the stepping translation table is used for placing the nonlinear crystal, and the light passage of the nonlinear crystal is adjusted through the stepping translation table, so that the tuning of multi-wavelength intermediate infrared output is realized.

Wherein the spacing of the two wavelengths is adjusted by laterally shifting the nonlinear crystal.

The semiconductor laser enters an alkali metal vapor chamber (5) through a polarizing device after being focused by an input mirror, and the input mirror is a focusing mirror or an off-axis parabolic mirror.

The polarizing device is a polarizing beam splitting cube or a Glan laser prism.

Wherein the positions of the alkali metal vapor chamber and the polarizing device can be interchanged.

The output coupling mirror has a certain output coupling ratio to the idler frequency light and the signal light, and outputs the idler frequency light and the signal light at the same time.

The output coupling mirror has a certain output coupling rate to the idler frequency light, the signal light and the alkali metal laser, and outputs the idler frequency light, the signal light and the alkali metal laser at the same time.

Has the advantages that:

the infrared light beams in the dual-wavelength system are generated in two nonlinear processes, the coupling degree between the two nonlinear frequency conversion processes is small, the threshold value generated by optical parametric oscillation is low, and the power ratio of each wavelength can be adjusted conveniently. The pumping light in the 2-time optical parametric oscillation process is generated by the same semiconductor laser, so that the infrared light beam in the dual-wavelength has the strict coaxial-axis characteristic, and the laser source is a high-quality laser source for gas differential absorption detection and terahertz generation.

Drawings

Fig. 1 is an overall schematic diagram of an optical parametric oscillator device outputting mid-infrared light of dual wavelengths according to the present invention.

The device comprises a 1-high reflection mirror, a 2-semiconductor laser, a 3-focusing mirror, a 4-polarization beam splitting cube, a 5-alkali metal air chamber, a 6-first temperature control furnace, a 7-dichroic mirror, an 8-neodymium-doped crystal, a 9-dichroic mirror, a 10-nonlinear crystal, a 11-second temperature control furnace and a 13-output coupling mirror.

FIG. 2 shows the structure of a multicycle polarized crystal according to the present invention.

Fig. 3 shows the pumping light passing through four different channels of the nonlinear crystal according to the present invention.

Detailed Description

The invention is described in detail below by way of example with reference to the accompanying drawings.

Semiconductor laser pumping alkali metal laser (DPAL) is a new type of optical pumping gas laser, whose gain medium is alkali metal atoms in vapor state, mainly potassium, rubidium or cesium vapor. The pumping wavelengths of the three alkali metal lasers are 766nm, 780nm and 852nm respectively, and the corresponding laser wavelengths are 770nm, 795nm and 895nm respectively. The thermal lens effect of DPAL is insignificant, the laser wavelength is stable and the operating temperature is close to the operating temperature range of nonlinear crystals. DPAL is a gas laser, has a narrow output laser spectrum when free-running, and produces near-infrared laser using it as a pumping source for neodymium-doped crystals.

As shown in fig. 1, the optical parametric oscillator device for outputting dual-wavelength mid-infrared light of the present invention includes a high-reflection mirror 1, a semiconductor laser 2, a focusing mirror 3, a polarization splitting cube 4, an alkali metal vapor chamber 5, a first temperature controlled oven 6, a dichroic mirror 7, a neodymium-doped crystal 8, a four-color mirror 9, a nonlinear crystal 10, a second temperature controlled oven 11, a stepping translation stage 12, and an output coupling mirror 13. The optical parametric oscillator places an alkali metal gas chamber 5, a neodymium-doped crystal 8 and a nonlinear crystal 10 in a resonant cavity of an alkali metal laser and a 1064nm laser, and realizes the output of dual-wavelength mid-infrared laser by simultaneously pumping the nonlinear crystal 10 through the alkali metal laser and the 1064nm laser.

The high-reflection mirror 1 reflects and oscillates the alkali metal laser, and forms a resonant cavity of the alkali metal laser with the output coupling mirror 13 to realize optical amplification on the alkali metal laser. In this embodiment, the high reflecting mirror 1 reflects the oscillated rubidium laser, and the reflectivity is higher than 99.5%, so as to form a rubidium laser resonant cavity with the output coupling mirror 13.

The semiconductor laser 2 outputs semiconductor laser light, which functions to pump the alkali metal vapor chamber 5 in the first temperature controlled furnace 6, and to realize population inversion between the upper level and the lower level of the laser light. The light beam output from the semiconductor laser 2 is incident on the focusing mirror 3. In the present embodiment, the wavelength of the semiconductor laser in the air is 780.02nm, and the line width is 0.1 nm.

The focusing mirror 3 focuses the pump light for improving the power density of the pump light, the light beam focused by the focusing mirror 3 is incident to the polarization beam splitter cube 4, and the focus is in the alkali metal vapor chamber 5. The focusing mirror 3 can be replaced by an off-axis parabolic mirror, and aims to reflect and focus semiconductor laser and improve the power density of the semiconductor laser.

In this embodiment, the polarization device 4 is a polarization beam splitter cube, and functions to linearly polarize the alkali metal laser and couple the semiconductor laser with the alkali metal laser; the semiconductor laser and the alkali metal laser pass through the polarization beam splitter cube 4 in different polarization states, wherein the polarization state of the semiconductor laser is vertically linear polarization (S polarization), and the polarization state of the rubidium laser is parallel linear polarization (P polarization). The semiconductor laser is converged into the alkali metal vapor chamber 5 through the polarization beam splitter cube 4. In this embodiment, the focal length of the focusing lens 3 is 75mm, the clear aperture is phi 50mm, and the diameter of the focus converged into the alkali metal vapor chamber 5 is 0.8 mm. Other types of polarizing devices, such as a glan laser prism, may be substituted.

The alkali metal vapor chamber 5 is filled with an alkali metal simple substance and buffer gas, is a working substance of an alkali metal laser, and can realize the population inversion of the upper and lower energy levels of the alkali metal atom laser after the focused semiconductor laser pumping to generate the gain of the alkali metal laser corresponding to the wavelength. After being amplified by a resonant cavity formed by the high-reflection mirror and the output coupling mirror, the amplified laser light is used as pumping light in a first-stage parametric oscillation process. In this embodiment, the alkali metal vapor chamber 5 is a rubidium vapor chamber filled with rubidium simple substance and methane, and is a working substance of a rubidium laser, and the methane pressure is selected to be 80 kPa. After being pumped by the focused semiconductor laser, the particle number of upper and lower energy levels of rubidium atomic laser can be turned over.

The first temperature control furnace 6 is used for controlling the temperature of the alkali metal vapor chamber 5 and providing working temperature conditions required by the working of the alkali metal laser. In this embodiment, the operating temperature is set to 145 ℃.

The dichroic mirror 7 is a coated lens, which has high transmittance for alkali metal laser and high reflectance for 1064nm laser, and forms a 1064nm laser resonant cavity with the output coupling mirror 13, and realizes light amplification for 1064nm laser. In this embodiment, the reflectivity of the dichroic mirror 7 to 1064nm laser is higher than 99%, and the transmittance to rubidium laser wavelength (795nm) is higher than 99%.

The neodymium-doped crystal 8 generates stimulated radiation of 1064nm after being pumped by alkali metal laser, and the stimulated radiation is amplified by a resonant cavity formed by the output coupling mirror 13 and the dichroic mirror 7 and is used as pumping light in a secondary parametric oscillation process. The neodymium-doped crystal 8 can be a double-end bonded crystal, and mode matching of alkali metal laser in the neodymium-doped crystal 8 is guaranteed. In this embodiment, the Nd-doped crystal 8 is Nd: YVO₄And (4) crystals.

The four-color mirror 9 is a coated lens, which has high reflection to the mid-infrared laser, high transmission to the alkali metal laser and 1064nm laser, and forms a resonant cavity mirror of the optical parametric oscillator with the output coupling mirror 13. In the embodiment, the reflectivity of the optical fiber to a wave band of 3.0-3.6 microns is higher than 99%, the transmissivity of the optical fiber to rubidium laser wavelength (795nm) and 1064nm is higher than 99%, and the reflectivity of the optical fiber to semiconductor laser wavelength is higher than 95%.

The nonlinear crystal 10 is a multicycle-polarized nonlinear crystal, and each cycle satisfies the momentum conservation condition of optical parametric oscillation when pumping with an alkali metal laser and a 1064nm laser.

The nonlinear crystal can be magnesium-doped periodically poled lithium niobate (MgO: PPLN crystal) or periodically poled lithium niobate (PPLN crystal). This example uses a MgO PPLN crystal, which is a multi-period poled nonlinear crystal, and the structure of which is shown in FIG. 2. With four parallel channels, i.e. Λ, on the left side of the crystal_l1、Λ_l2、Λ_l3And Λ_l4The channel width is 1mm, the polarization periods are 21.6 μm, 21.5 μm, 21.4 μm and 21.3 μm respectively, and each period satisfies the momentum conservation condition of optical parametric oscillation when alkali metal laser pumping is used. With two parallel channels, i.e. Λ, on the right side of the crystal_r1And Λ_r2The channel width is 2mm, the polarization periods are 30.0 μm and 30.8 μm respectively, and each period meets the momentum conservation condition of optical parametric oscillation when 1064nm pumping is used.

MgO: the polarization period of the four channels at the left side of the PPLN crystal is lambda_l1、Λ_l2、Λ_l3And Λ_l4All satisfy the use of rubidium laser lambda₇₉₅And the conservation of momentum of optical parametric oscillation during pumping. Taking the first channel on the left as an example, the polarization period of the channel is Λ_l1Then, then

In the formula n₇₉₅，n_S1And n_I1Respectively the wavelength lambda of the pump light₇₉₅Signal light wavelength lambda_S1And idler wavelength λ_I1The corresponding refractive index in the first channel on the left side of the crystal.

MgO: the PPLN crystal is a medium for generating a nonlinear phenomenon, and the nonlinear phenomenon is generated by rubidium laser pumping. The length, the width and the height of the four channels on the left side are respectively 25mm, 1mm and 1mm, the polarization periods are respectively 21.6 microns, 21.5 microns, 21.4 microns and 21.3 microns, and the end faces are plated with anti-reflection films of 700-4000 nm. Under the four polarization periods, the wavelengths of idle frequency light which can be output are respectively 3.19 μm, 2.99 μm, 2.86 μm and 2.73 μm, and the wavelengths of signal light which can be output are respectively 1.06 μm, 1.08 μm, 1.10 μm and 1.12 μm.

MgO: the polarization periods of the two channels on the right side of the PPLN crystal are Λ_r1And Λ_r2The condition of conservation of momentum of optical parametric oscillation when 1064nm pumping is used is satisfied. Taking the first channel on the right as an example, the polarization period of the channel is Λ_r1Then, then

In the formula n₁₀₆₄，n'_S1And n'_I1Respectively the wavelength lambda of the pump light₁₀₆₄And signal light wavelength lambda'_S1And idler wavelength λ'_I1The corresponding refractive index in the first channel on the right side of the crystal.

MgO: the PPLN crystal is a medium for generating a nonlinear phenomenon, and the nonlinear phenomenon is generated by 1064nm pumping. The length, the width and the height of the two channels on the right side are respectively 25mm, 2mm and 1mm, the polarization periods are respectively 30.0 mu m and 29.8 mu m, and the end faces are plated with antireflection films of 700-4000 nm. Under the two polarization periods, the wavelengths of the idle frequency light and the signal light can be respectively 3.39 μm and 3.50 μm, and the wavelengths of the signal light and the signal light can be respectively 1.55 μm and 1.53 μm.

The second temperature controlled furnace 11 controls the temperature of the nonlinear crystal. The temperature of the nonlinear crystal is used to make the output wavelength of the optical parametric oscillator be lambda_S1Signal light of (2) and wavelength of λ_I1The idler light of (1). In this embodiment, the control accuracy of the second temperature-controlled furnace 11 is 0.1 ℃, the initial temperature of the nonlinear crystal is set to 25 ℃, and the control and optimization of the working temperature of the nonlinear crystal are performed with this accuracy, so as to tune the output wavelength of the dual-wavelength mid-infrared laser.

The stepping translation stage 12 is controlled by a stepping motor with repetition accuracy better than 10nm and is used for placing a second temperature control furnace 11 and MgO: the PPLN crystal realizes the tuning of multi-wavelength mid-infrared output by controlling a non-linear crystal light-passing channel by using a stepping motor. As shown in FIG. 3, the light-passing channel of the multicycle polarized MgO PPLN crystal can be controlled by the movement of the stepping translation stage, so that the alkali metal laser and the 1064nm pumped MgO PPLN crystal can be ensured to be assigned to the channel, and the tuning of the multi-wavelength mid-infrared laser output can be realized.

The output coupling mirror 13 outputs the mid-infrared laser, the surface of which is plated with a dielectric film, the dielectric film has high reflection to the alkali metal laser and the 1064nm laser, and the mid-infrared laser has a certain output coupling rate. And the four-color mirror 9 forms a resonant cavity of the optical parametric oscillator to realize optical amplification on mid-infrared laser. And a resonant cavity of 1064nm laser is formed with the dichroic mirror 7, and light amplification is realized on the 1064nm laser. And the high-reflection mirror 1 forms a resonant cavity of the alkali metal laser to realize optical amplification of the alkali metal laser. The output coupling mirror 13 may also have a certain output coupling ratio for both the idler light and the signal light, and the output coupling ratios for the idler light and the signal light may be the same or different, so as to output the idler light and the signal light at the same time; the output coupling rates of the idler frequency light, the signal light and the alkali metal laser can be the same or different, and the aim of simultaneously outputting the idler frequency light, the signal light and the alkali metal laser is fulfilled.