CN115656042B - Large-rotation-angle tuning medium-and-long-wave infrared coherent light source device with stable light beam direction - Google Patents

Abstract

The invention relates to a long-wave infrared coherent light source device in large-angle tuning with stable beam pointing, which comprises a pulse laser, an isolator, an Optical Parametric Oscillator (OPO) input mirror, a nonlinear crystal, an OPO output mirror, a long-pass filter, a fixed right-angle prism and a movable right-angle prism. The laser is used for generating pump light; the pulse isolator is used for ensuring unidirectional laser transmission; the OPO input mirror, the nonlinear crystal and the OPO output mirror are used for generating medium-long wave infrared light; the long-pass filter is used for blocking residual pump light; the fixed right angle prism and the displacement right angle prism are used for compensating the transverse displacement of the output light beam caused in the rotation process of the crystal. The invention compensates the transverse displacement of the light beam by correspondingly moving the prism, realizes the invariable position of the output light beam with large rotation angle tuning, ensures the stable directivity of the output light beam and is beneficial to the subsequent application research. The invention has simple structure and simple and convenient operation, and is suitable for the requirements of infrared molecular spectrum, medical imaging, remote sensing and the like.

Description

Large-angle tunable mid- and long-wave infrared coherent light source device with stable beam pointing

Technical Field

The invention relates to the technical field of mid-infrared optics, in particular to a large-angle-tuned mid- and long-wave infrared coherent light source device with stable light beam pointing.

Background technique

The mid- and long-wave infrared band generally refers to the electromagnetic spectrum range with a wavelength of 2.5-25μm, which is an important transition area from visible light to terahertz waves. The mid- and long-wave infrared band includes two important atmospheric windows of 3-5μm and 8-12μm. Mid-wave infrared (3-5μm) lasers have very important applications in the military field and are widely valued. In addition, the mid-infrared 8-14μm band is in the molecular fingerprint area of the substance. The molecular absorption peaks in this area are numerous and complex, and there is no strong characteristic. When the molecular structure is slightly different, the absorption of this area will have slight differences. The fingerprints of many important substances such as CF4, NH3, O3 and glucose are all in the 8-14μm band. The spectral analysis technology of the 8-14μm continuously tuned laser can realize the accurate detection and identification of the above important substances.

So far, there is no corresponding laser gain medium that can directly obtain 3-17μm tunable laser. Generally, optical parametric oscillation (OPO) is used to obtain laser output in this band. Many parameters of medium and long-wave infrared coherent light sources have an important impact on the system, such as power, energy, divergence angle, spot size, repetition frequency, etc. The pointing stability of the laser output beam is also one of the important parameters of the light source. It will reflect the output effect of the laser beam and affect its development in the above-mentioned application fields. The angle tuning method used in this patent is currently the fastest and largest tuning method. If the wavelength range of the output laser is to cover 3-17μm, this tuning method is currently simple and feasible. However, during the tuning process, this method will cause lateral displacement of the output beam due to the rotation of the nonlinear crystal, change the beam pointing direction, and affect subsequent applications.

Summary of the invention

In view of the shortcomings of the prior art, the present invention provides a large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing, which generates medium- and long-wave infrared light by using the interaction between pump light and nonlinear crystal, realizes output wavelength tuning by rotating nonlinear crystal, and keeps the beam pointing stable according to the relationship between the beam offset distance generated by tuning and the required compensation displacement of the right-angle prism. The present invention can be applied to infrared molecular spectroscopy, medical imaging, remote sensing, etc.

The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

A large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing comprises a pulse laser, an isolator, an optical parametric oscillator (OPO) input mirror, a nonlinear crystal, an OPO output mirror, a long-pass filter, a fixed right-angle prism and a movable right-angle prism arranged in sequence along the light output direction of a pump light source;

The pulse laser emits a pump beam; the isolator enables the pump beam to be transmitted unidirectionally; the light-transmitting surfaces of the isolator, the OPO input mirror and the OPO output mirror are parallel to each other, and each light-transmitting surface is perpendicular to the pump beam;

The OPO input mirror and the OPO output mirror together form a resonant cavity, and the angle θ between the central axis of the nonlinear crystal and the pump light beam is variable; the resonant cavity is used to make the input pump light oscillate with the nonlinear crystal in the cavity to generate signal light and medium- and long-wave infrared idler light; the OPO output mirror outputs the remaining pump light and medium- and long-wave infrared idler light;

The light-passing end face of the filter forms an angle of 45° with the remaining pump light beam, and is used to reflect the remaining pump light and transmit the mid- and long-wave infrared idler light;

The fixed right-angle prism and the movable right-angle prism are placed inversely with their inclined surfaces parallel to each other, forming a parallel refraction structure; the lateral relative position distance L between the movable right-angle prism and the fixed right-angle prism is variable, so as to change the effective thickness of the refraction structure.

The pulse laser is a neodymium-doped yttrium aluminum garnet laser; the pulse laser generates pump light with a wavelength of 1064nm; the isolator is a spatial light isolator coated with a 1064nm anti-reflection film.

The OPO input mirror is a plane mirror, the lens material is K9 glass, the incident surface is coated with a pump light anti-reflection film, and the output surface is coated with a pump light anti-reflection film and a signal light high-reflection film; the OPO output mirror is a plane mirror, the lens material is ZnSe, the incident surface is coated with pump light high-transmittance, signal light high-reflection and medium- and long-wave infrared light high-transmittance films, and the output surface is coated with pump light high-transmittance and medium- and long-wave infrared high-transmittance films.

The nonlinear crystal material is non-oxide gallium-barium selenide crystal.

The long-pass filter is made of high-resistance Ge, and its surface is coated with a near-infrared high-reflection film and a 3-17μm medium- and long-wave infrared light anti-reflection film.

The fixed right-angle prism and the movable right-angle prism are both straight triangular prisms with an isosceles right triangle as the base, made of ZnSe, and coated with a 3-17 μm mid-infrared anti-reflection film on the surface.

The nonlinear crystal is arranged on a horizontal turntable, and the turntable rotates to change the angle θ between the central axis of the nonlinear crystal and the pump light beam.

The movable right-angle prism is arranged on a horizontal one-dimensional linear translation stage, and can adjust its lateral relative position distance L with the fixed right-angle prism along a direction perpendicular to the medium and long-wave infrared idler light, thereby changing the effective thickness of the refractive structure and compensating for the lateral displacement deviation of the output direction of the medium and long-wave infrared idler light beam caused by the nonlinear crystal rotation during the tuning process.

It also includes a host computer, which is connected to the horizontal turntable below the nonlinear crystal and the one-dimensional linear displacement stage below the movable right-angle prism, and is used for outputting command signals to control the operation of each device.

A method for controlling a large-angle tunable medium- and long-wave infrared coherent light source with stable beam pointing comprises the following steps:

Step 1: pre-calibrate the relationship model between the angle θ and the lateral relative position distance L: L = a×θ ³ + b×θ ² + c×θ + d, where a, b, c, d are model coefficients after multiple pre-calibrations;

Step 2: adjusting and detecting in real time the angle θ between the central axis of the nonlinear crystal 4 and the pump beam;

Step 3: Calculate the following lateral relative position distance L corresponding to the current angle θ according to the relationship model;

Step 4: Adjust the movable right-angle prism 8 along the direction perpendicular to the medium and long-wave infrared idler light, and adjust its lateral relative position distance L with the fixed right-angle prism 7 to the value calculated in step 3, so as to change the effective thickness of the refractive structure, compensate for the lateral displacement deviation of the medium and long-wave infrared idler light beam in the output direction caused by the large rotation angle of the nonlinear crystal 4 during the tuning process, and realize the stability of the beam pointing.

The present invention has the following beneficial effects and advantages:

1. The present invention utilizes the interaction of pump light in a nonlinear crystal to generate medium- and long-wave infrared light, and achieves tunable output of medium- and long-wave infrared light by rotating the angle of the nonlinear crystal and changing the phase matching condition.

2. The nonlinear crystal used in the present invention is a non-oxide barium gallium selenide (BaGa ₄ Se ₇ ) crystal, which has a large transparent band, a large second-order nonlinear coefficient and a high damage threshold. At the same time, the dielectric properties of the crystal ensure the phase matching of the pump light, which is conducive to achieving efficient output in the tunable infrared band (wavelength 3-17μm).

3. The method for compensating beam displacement adopted by the present invention uses a translation stage to move the position of the prism to compensate for the beam displacement caused by the crystal rotation tuning, so that the beam does not shift due to tuning and remains at the position required by the subsequent optical path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a three-dimensional schematic diagram of an embodiment of a large-angle tunable medium- and long-wave infrared coherent light source device with stable light beam pointing provided by the present invention;

FIG2 is a top view of an embodiment of a large-angle tunable medium- and long-wave infrared coherent light source device with stable light beam pointing provided by the present invention;

FIG3 is a flow chart of a control method of the device of the present invention;

Among them, 1 is a pulse laser, 2 is an isolator, 3 is an OPO input mirror, 4 is a nonlinear crystal, 5 is an OPO output mirror, 6 is a long-pass filter, 7 is a fixed right-angle prism, and 8 is a movable right-angle prism.

Detailed ways

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation method of the present invention is described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the invention, so the present invention is not limited by the specific implementation disclosed below.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

The present invention is further described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the present invention provides a large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing, including a pulse laser 1 and an isolator 2, an OPO input mirror 3, a nonlinear crystal 4, an OPO output mirror 5, a long-pass filter 6, a fixed right-angle prism 7, and a movable right-angle prism 8, which are arranged in sequence in the direction of the medium- and long-wave infrared output beam. The pulse laser 1 emits the pump light required by the medium and long wave infrared light source; the passing surfaces of the isolator 2, OPO input mirror 3, and OPO output mirror 5 are parallel to each other, and each passing surface is perpendicular to the input pump light beam (that is, the generated medium and long wave infrared light); the long pass filter 6 is arranged behind the OPO output mirror 5, and its passing end face is at a 45° angle to the pump output light beam, blocking the pump light emitted from the OPO output mirror 5, and reflecting the pump light transmitted by the pulse laser 1 along a direction perpendicular to the medium and long wave infrared light output light beam, so that the light passing through the long pass filter 6 is all medium and long wave infrared light; the isolator 2 is used to ensure unidirectional transmission of the laser to avoid damage to the pulse laser 1 caused by the return light; the OPO input mirror 3 and the OPO output mirror 5 together constitute a resonant cavity, and the pump light enters the OPO resonant cavity , the signal light and idler light generated in the cavity, the signal light repeatedly oscillates in the cavity, and the mid-infrared light and idler light are transmitted and output; the nonlinear crystal 4 meets the phase matching condition of parametric oscillation (the phase matching is achieved by using the birefringence and dispersion characteristics of the crystal), realizes efficient energy conversion and mid- and long-wave infrared tuning output, and the angle θ between the central axis of the nonlinear crystal 4 and the pump beam is variable; the long-pass filter 6 blocks the remaining pump light and outputs mid- and long-wave infrared light; the fixed right-angle prism 7 and the movable right-angle prism 8 are placed inversely, with parallel inclined surfaces, forming a parallel refraction structure, by adjusting the lateral position of the prism 8 along the direction perpendicular to the mid- and long-wave infrared idler light, changing the relative position L of the movable right-angle prism 8 and the fixed right-angle prism 7, changing the effective thickness of the refraction structure, and compensating for the beam displacement caused by the rotation of the nonlinear crystal 4 during the tuning process. The movable right-angle prism 8 uses refraction to compensate for the offset of the mid- and long-wave infrared beam output after the fixed right-angle prism 7 due to the rotation of the nonlinear crystal 4, so that the position of the output beam remains unchanged.

As shown in FIG3 , the output wavelength of the mid- and long-wave infrared light source is adjusted by rotating the nonlinear crystal and changing the phase matching angle θ.

Working principle of the device:

Step 1: pre-calibrate the relationship model between the angle θ and the lateral relative position distance L: L = a×θ ³ + b×θ ² + c×θ + d, where a, b, c, d are model coefficients after multiple pre-calibrations. The relationship model is used to compensate for the displacement of the mid- and long-wave infrared idler light beam in the output direction caused by the rotation of the nonlinear crystal 4 during the tuning process;

Step 2: adjusting and detecting in real time the angle θ between the central axis of the nonlinear crystal 4 and the pump beam;

Step 3: Calculate the following distance L corresponding to the current angle θ according to the relationship model;

Step 4: Adjust the movable right-angle prism 8 in a direction perpendicular to the direction of the medium and long-wave infrared idle light, and adjust its relative position L with the fixed right-angle prism 7 to the position calculated in step 3, thereby changing the effective thickness of the refractive structure (referring to the optical path of the light propagating in the fixed right-angle prism 7 and the movable right-angle prism 8), compensating for the lateral displacement deviation in the output direction of the medium and long-wave infrared idle light beam caused by the large rotation angle of the nonlinear crystal 4 during the tuning process, and achieving beam pointing stability.

Embodiment 1:

Furthermore, the manual adjustment of Example 1 can be adopted: in step 2, the angle θ between the central axis of the nonlinear crystal 4 and the pump beam is manually adjusted; in step 4, the relative position distance L between the right-angle prism 8 and the fixed right-angle prism 7 is moved.

Embodiment 2:

Furthermore, on the basis of the device of the above-mentioned embodiment 1, the technical solution of the embodiment 2 for automatic adjustment can be obtained by setting a mobile device, as shown in Figure 2. The nonlinear crystal 4 is arranged on a turntable, and the turntable is connected to the host computer. The mobile right-angle prism 8 is arranged on a one-dimensional linear motion module, and the motor on the one-dimensional linear motion module is connected to the host computer. The host computer is provided with a program module, and when the program is executed, instructions are output to the turntable (electric rotating table) (the ultra-small 5-phase stepper motor automatic platform of Sigma company model OSCM-25YAM, the controller below is connected to the external computer for controlling the movement of the turntable, the center of the platform is embedded with a circular adapter plate, the cylindrical support rod is fixed at the center of the adapter plate, and the crystal is pasted on the other end of the support rod), the one-dimensional linear motion module, and the following process steps are implemented, as shown in Figure 3:

Step S1: pre-calibrate the relationship model between the angle θ and the distance L: L=a×θ ³ +b×θ ² +c×θ+d, wherein a, b, c, d are model coefficients after multiple pre-calibrations, and the relationship model is used to compensate for the displacement in the output direction of the medium and long wave infrared idler light beam caused by the rotation of the nonlinear crystal 4 during the tuning process;

Step S2: the turntable feeds back the angle, and detects the angle θ between the central axis of the nonlinear crystal 4 and the pump beam in real time through the turntable, and feeds back the angle θ to the computer program interface;

Step S3: Calculate the following lateral relative position distance L corresponding to the current angle θ according to the relationship model;

Step S4: Control the rotation of the motor on the one-dimensional linear motion module to drive the mobile right-angle prism 8 to adjust its lateral relative position distance L with the fixed right-angle prism 7 along the direction perpendicular to the medium and long-wave infrared idle light to the value calculated in step 3, thereby changing the effective thickness of the refractive structure (referring to the optical path of the light propagating in the fixed right-angle prism 7 and the mobile right-angle prism 8), compensating for the lateral displacement deviation in the output direction of the medium and long-wave infrared idle light beam caused by the large rotation angle of the nonlinear crystal 4 during the tuning process, and achieving beam pointing stability.

In actual application, pulse laser 1 is a commercial neodymium-doped yttrium aluminum garnet (Nd:YAG) Q-switched laser that outputs near-infrared light as pump light with a wavelength of 1064nm. Isolator 2 is a spatial optical isolator coated with a 1064nm anti-reflection film to ensure that the pump light passes in one direction, passes through the OPO input mirror 3, enters the nonlinear crystal 4, and generates medium and long-wave infrared light through the second-order nonlinear optical frequency conversion. By rotating the nonlinear crystal 4, the phase matching conditions are changed to achieve tunable medium and long-wave infrared light output. The OPO input mirror 3 is a plane mirror, K9 glass, and the surface is coated. The incident surface is coated with a pump light anti-reflection film, and the output surface is coated with a pump light anti-reflection film and a signal light high-reflection film. The nonlinear crystal 4 is a new type of non-oxide nonlinear crystal, made of barium gallium selenide (BaGa ₄ Se ₇ ), with a light-transmitting surface size of 10×7 mm ² and a length of 15 mm. The crystal has a large second-order nonlinear coefficient and a high damage threshold. At the same time, the dielectric properties of the crystal ensure the phase matching of the parametric oscillation process, which is conducive to achieving efficient energy conversion and mid-infrared light output. The wavelength tuning is achieved by changing the incident angle of the nonlinear crystal. The OPO output mirror 5 is a plane mirror with a coating on the surface. The lens material is ZnSe. The incident surface is coated with a high-transmittance film for pump light, a high-reflection film for signal light, and a high-transmittance film for mid- and long-wave infrared light. The output surface is coated with a high-transmittance film for pump light and a high-transmittance film for mid- and long-wave infrared light. The long-pass filter 6 is a high-resistance Ge substrate, and the surface is coated with a near-infrared light high-reflection film and a 3-17μm mid- and long-wave infrared light anti-reflection film, which is used to filter out the remaining pump light and achieve pure mid- and long-wave infrared light output. The fixed right-angle prism 7 and the displacement right-angle prism 8 are both right triangular prisms with an isosceles right triangle as the base, a right angle side length of 25 mm, a height of 25 mm, a material of ZnSe, and a 3-17 μm mid-infrared anti-reflection film coated on the surface to reduce the reflection loss of mid-infrared light.

The above device using right-angle prism translation to compensate for beam deviation caused by medium and long-wave infrared tuning can be used for applied research such as molecular spectroscopy, medical imaging, remote sensing, etc. The optical path structure is simple and compact, and the operation is simple and suitable for popularization in practical systems.

Claims (10)

1. A large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing, characterized in that it comprises a pulse laser (1), an isolator (2), an optical parametric oscillator (OPO) input mirror (3), a nonlinear crystal (4), an OPO output mirror (5), a long-pass filter (6), a fixed right-angle prism (7) and a movable right-angle prism (8) arranged in sequence along the light output direction of a pump light source; the pulse laser (1) emits a pump light beam; the isolator (2) enables the pump light beam to be transmitted unidirectionally; the light-transmitting surfaces of the isolator (2), the OPO input mirror (3) and the OPO output mirror (5) are parallel to each other, and each light-transmitting surface is perpendicular to the pump light beam; the OPO input mirror (3) and the OPO output mirror (5) are arranged in sequence along the light output direction of a pump light source; The nonlinear crystal (4) and the nonlinear crystal (4) form a resonant cavity, wherein the angle θ between the central axis and the pump light beam is variable; the resonant cavity is used to make the input pump light oscillate with the nonlinear crystal (4) in the cavity to generate signal light and medium- and long-wave infrared idler light; the OPO output mirror (5) outputs the remaining pump light and the medium- and long-wave infrared idler light; the light-transmitting end face of the filter (6) forms an angle of 45° with the remaining pump light beam, and is used to reflect the remaining pump light and transmit the medium- and long-wave infrared idler light; the fixed right-angle prism (7) and the movable right-angle prism (8) are placed inversely and with parallel inclined surfaces, forming a parallel refraction structure; the lateral relative position distance L between the movable right-angle prism (8) and the fixed right-angle prism (7) is variable, and is used to change the effective thickness of the refraction structure. 2. The large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing according to claim 1 is characterized in that the pulse laser (1) is a neodymium-doped yttrium aluminum garnet laser; the pulse laser (1) generates pump light with a wavelength of 1064nm; and the isolator (2) is a spatial light isolator coated with a 1064nm anti-reflection film. 3. The large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing according to claim 1 is characterized in that the OPO input mirror (3) is a plane mirror, the lens material is K9 glass, the incident surface is coated with a pump light anti-reflection film, and the exit surface is coated with a pump light anti-reflection film and a signal light high-reflection film; the OPO output mirror (5) is a plane mirror, the lens material is ZnSe, the incident surface is coated with pump light high-transmittance, signal light high-reflection and medium- and long-wave infrared light high-transmittance films, and the exit surface is coated with pump light high-transmittance and medium- and long-wave infrared high-transmittance films. 4. The large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing according to claim 1, characterized in that the nonlinear crystal (4) is made of non-oxide gallium-barium selenide crystal. 5. The large-angle tunable medium- and long-wave infrared coherent light source device with stable light beam pointing according to claim 1 is characterized in that the long-pass filter (6) is made of high-resistance Ge, and its surface is coated with a near-infrared high-reflection film and a 3-17 μm medium- and long-wave infrared light anti-reflection film. 6. The large-angle tunable mid- and long-wave infrared coherent light source device with stable beam pointing according to claim 1 is characterized in that the fixed right-angle prism (7) and the movable right-angle prism (8) are both right triangular prisms with an isosceles right triangle as the base, made of ZnSe, and coated with a 3-17 μm mid-infrared anti-reflection film on the surface. 7. The large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing according to claim 1, characterized in that the nonlinear crystal (4) is arranged on a horizontal turntable, and the turntable rotates to change the angle θ between the central axis of the nonlinear crystal (4) and the pump beam. 8. The large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing according to claim 1 is characterized in that the movable right-angle prism (8) is arranged on a horizontal one-dimensional linear displacement stage, and can adjust its lateral relative position distance L with the fixed right-angle prism (7) along a direction perpendicular to the medium- and long-wave infrared idler light, thereby changing the effective thickness of the refractive structure and compensating for the lateral displacement deviation of the output direction of the medium- and long-wave infrared idler light beam caused by the rotation of the nonlinear crystal (4) during the tuning process. 9. The large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing according to any one of claims 7 or 8 is characterized in that it also includes a host computer, which is connected to the horizontal turntable below the nonlinear crystal (4) and the one-dimensional linear translation stage below the movable right-angle prism (8) to output command signals to control the operation of each device. 10. The control method of the large-angle tunable medium- and long-wave infrared coherent light source device with stable beam pointing according to any one of claims 1 to 9, comprising the following steps: Step 1: Pre-calibrate the relationship model between the angle θ and the lateral relative position distance L : L = a × θ ³ + b × θ ² + c × θ + d , where a, b, c, d are model coefficients after multiple pre-calibrations; Step 2: Adjust and detect in real time the angle θ between the central axis of the nonlinear crystal (4) and the pump beam; Step 3: Calculate the following lateral relative position distance L corresponding to the current angle θ according to the relationship model; Step 4: Adjust the movable right-angle prism (8) in a direction perpendicular to the direction of the medium- and long-wave infrared idler light, and adjust the lateral relative position distance L between the movable right-angle prism (8) and the fixed right-angle prism (7) to the value calculated in step 3, so as to change the effective thickness of the refractive structure, compensate for the lateral displacement deviation of the medium- and long-wave infrared idler light beam in the output direction caused by the large rotation angle of the nonlinear crystal (4) during the tuning process, and realize the stabilization of the beam pointing.