Large-angle-tuning short-wave infrared coherent light source with beam pointing stability

Abstract

The present application relates to a kind of light beam pointing stability large rotation angle tuning short wave infrared coherent light source, and the present coherent light source includes: pump laser, magneto-optical isolator, condensing lens group, two 45 ° reflector, optical parametric oscillator (OPO), optical filter, fixed right-angle prism and mobile right-angle prism.The pump laser is used to generate pump light;The magneto-optical isolator is used to ensure one-way transmission of laser;The condensing lens group is used to improve beam energy density;Two 45 ° reflector is used to fold pump light path;The optical parametric oscillator is used to generate coherent short wave infrared light;The nonlinear crystal is used to adjust the output wavelength of short wave infrared light source;The optical filter is used to block remaining pump light;Fixed right-angle prism and displacement right-angle prism are used to compensate the lateral displacement of output beam caused in the process of crystal rotation.The present application compensates the lateral displacement of light beam by moving prism, realizes the position of output beam unchanged in the process of large rotation angle tuning, ensures its directionality stability, and is suitable for spectral analysis, remote sensing and imaging and other needs.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of infrared optical technology, in particular to a large-angle tuning short-wave infrared coherent light source with stable beam pointing. BACKGROUND

[0002] Since the advent of laser, due to its outstanding performance in directivity, monochromaticity and coherence, laser technology has developed rapidly and has been widely used in national defense, medical treatment and communication. However, due to the traditional waveband division, 2.5 μm as the dividing line between near-infrared light and mid-infrared light, the development level of the light source centered on 2.5 μm is slightly lagging behind, and the research fields such as spectral analysis, remote sensing and imaging need the coherent light source of this waveband.

[0003] At present, there is no corresponding laser gain medium to directly obtain the tunable laser of 1.6-3.2 μm full coverage, and the laser output of this waveband is generally obtained by using the optical parametric oscillator, in which the angle tuning with the advantages of large range, rapid and simple operation becomes a commonly used method. If the full coverage of the output coherent light of 1.6-3.2 μm wavelength range is to be realized, this tuning method is currently effective. However, in the tuning process, the rotation of the nonlinear crystal will cause the transverse displacement of the output light beam, change the beam pointing and affect the subsequent use. SUMMARY

[0004] The present application provides a large-angle tuning short-wave infrared coherent light source with stable beam pointing, which utilizes the interaction between pump light and nonlinear crystal to generate coherent short-wave infrared light, realizes the tunable output of the output wavelength by rotating the 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 short-wave infrared coherent light source with a normal incidence wavelength of 2.5 μm and a tuning range of 1.6-3.2 μm can be outputted.

[0005] A large-angle tuning short-wave infrared coherent light source with stable beam pointing, comprising a pump laser, a magneto-optical isolator, a convex lens, a concave lens, an OPO input mirror, a nonlinear crystal, an OPO output mirror, a filter, a fixed right-angle prism and a movable right-angle prism arranged in sequence along the light emitting direction of the pump light source.

[0006] The pump laser emits a pump light beam; the magneto-optical isolator makes the pump light transmit in one direction; the axes of the convex lens and the concave lens are coincided with the pump laser beam, and the concave lens is arranged at the focal point of the convex lens.

[0007] The optical parametric oscillator comprises a resonant cavity composed of an OPO input mirror and an OPO output mirror, and a nonlinear crystal in the resonant cavity; an angle θ between an axis of the nonlinear crystal and a pump light beam is variable; the resonant cavity is used for frequency down-conversion of the input pump light under the action of the nonlinear crystal in the cavity to generate short-wave infrared signal light with a wavelength of 1.6-3.2 μm and idler light; and the OPO output mirror outputs the remaining pump light and idler light.

[0008] The filter is used for reflecting the remaining pump light and transmitting the short-wave infrared light.

[0009] The fixed right-angle prism and the movable right-angle prism are reversely placed, the inclined surfaces are parallel, and the fixed right-angle prism and the movable right-angle prism constitute a parallel refraction structure; a transverse relative position of the movable right-angle prism to the fixed right-angle prism is variable, and is used for changing an effective thickness of the refraction structure.

[0010] The pump laser is a neodymium-yttrium-aluminum garnet laser, and the output pump laser has a wavelength of 1.064 μm; the magneto-optical isolator is a spatial light isolator, and a 1.064 μm anti-reflection film is coated on the magneto-optical isolator.

[0011] Further comprising: a first 45° reflecting mirror and a second 45° reflecting mirror are arranged between the concave lens and the OPO input mirror, and the pump light is reflected to change a light path direction.

[0012] The OPO input mirror is a plane mirror, is made of K9 glass, has a pump light anti-reflection film coated on an incident surface, and has a pump light anti-reflection film and a signal light high-reflection film coated on an emergent surface; the OPO output mirror is a plane mirror, is made of CaF2, has a pump light high-transmission film, a signal light high-reflection film and an idler light high-transmission film coated on an incident surface, and has a pump light high-transmission film and an idler light high-transmission film coated on an emergent surface.

[0013] The filter is made of CaF2, and has a pump light high-reflection film and a 1.6-3.2 μm short-wave infrared light anti-reflection film coated on a surface.

[0014] The fixed right-angle prism and the movable right-angle prism are both right prisms with an isosceles right triangle as a bottom surface, are made of CaF2, and have a 1.6-3.2 μm short-wave infrared light anti-reflection film coated on a surface.

[0015] The nonlinear crystal is a potassium titanyl phosphate crystal; the nonlinear crystal is arranged on a horizontal rotary table, and a rotation of the rotary table changes the angle θ between the axis of the nonlinear crystal and the pump light beam.

[0016] The movable right-angle prism is arranged on a horizontal one-dimensional linear displacement table, and can adjust a relative position L of the movable right-angle prism to the fixed right-angle prism along a direction perpendicular to the idler light direction, so as to change the effective thickness of the refraction structure and compensate for a transverse displacement deviation of an output direction of the short-wave infrared idler light beam caused by the rotation of the nonlinear crystal in a tuning process.

[0017] It also includes a host computer, which is connected to the pump laser, magneto-optical isolator, horizontal turntable below the nonlinear crystal, and one-dimensional linear displacement stage below the movable right-angle prism, and is used to output command signals to control the operation of each device.

[0018] A method for controlling a large-angle tuned medium-long-wave infrared coherent light source with stable beam pointing includes the following steps:

[0019] Step 1: Pre-determine the relationship model between the included angle θ and the distance L: L = A × (θ) 3 )+B×(θ 2 )+C×θ+D; where A, B, C, and D are model coefficients that have been pre-calibrated multiple times;

[0020] Step 2: Adjust and monitor in real time the angle θ between the axis of the nonlinear crystal 8 and the pump beam;

[0021] Step 3: Based on the relationship model, calculate the lateral relative position distance L corresponding to the current included angle θ;

[0022] Step 4: Adjust the lateral relative position distance L between the movable right-angle prism 12 and the fixed right-angle prism 11 along the idler beam direction to the value calculated in step 3. This is used to change the effective thickness of the refractive structure, compensate for the lateral displacement deviation in the output direction of the mid-to-long-wave infrared idler beam caused by the large rotation angle of the nonlinear crystal 8 during the tuning process, and achieve beam pointing stability.

[0023] The present invention has the following beneficial effects and advantages:

[0024] 1. The oxide nonlinear crystal (including but not limited to KTA) optical parametric oscillator used in this invention achieves the output of wide-tunable short-wave infrared coherent light by rotating the nonlinear crystal angle and changing the phase matching condition.

[0025] 2. The beam displacement compensation method used in this invention uses a translation stage to move the position of the prism to compensate for the beam displacement caused by the rotation and tuning of the crystal, thereby obtaining wide-tunable short-wave infrared light with stable beam direction, which greatly facilitates subsequent applications such as spectral analysis and small-size sample detection. Attached Figure Description

[0026] Figure 1 This is a three-dimensional schematic diagram of an embodiment of the large-angle tuned shortwave infrared coherent light source device with stable beam pointing provided by the present invention;

[0027] Figure 2 This is a top view of an embodiment of the large-angle tuned shortwave infrared coherent light source device with stable beam pointing provided by the present invention;

[0028] Figure 3is a control method flow chart of the device of the present application;

[0029] Wherein, 1 is a pump laser, 2 is a magneto-optical isolator, 3 is a convex lens, 4 is a concave lens, 5 is a first 45° mirror, 6 is a second 45° mirror, 7 is an OPO input mirror, 8 is a nonlinear crystal, 9 is an OPO output mirror, 10 is a filter, 11 is a fixed right-angle prism, and 12 is a moving right-angle prism. DETAILED DESCRIPTION

[0030] In order to make the above objectives, features and advantages of the present application more apparent, the specific implementation method of the present application will be described in detail below with reference to the accompanying drawings. In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many different ways other than those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present application, so the present application is not limited to the specific implementation disclosed below.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application.

[0032] As Figure 1As shown, the application provides a large-angle-tuning short-wave infrared coherent light source with beam pointing stability, which comprises a pump laser 1, a magneto-optical isolator 2, a concave lens 3, a convex lens 4, a first 45° mirror 5, a second 45° mirror 6, an OPO input mirror 7, a nonlinear crystal 8, an OPO output mirror 9, a filter 10, a fixed right-angle prism 11 and a movable right-angle prism 12. The pump laser 1 generates pump laser for the OPO, and the pump light passes through the magneto-optical isolator 2, the convex lens 3, the concave lens 4, the first 45° mirror 5, the second 45° mirror 6, the OPO input mirror 7, the nonlinear crystal 8, the OPO output mirror 9, the filter 10, the fixed right-angle prism 11 and the movable right-angle prism 12 in sequence. The magneto-optical isolator 2 ensures one-way transmission of the laser, avoiding damage to the laser caused by return light; the convex lens 3 and the concave lens 4 have their axes coinciding with the pump laser beam, for improving the energy density of the beam; the first 45° mirror 5 and the second 45° mirror 6 are used for reflecting the pump light, making the structure more compact; the optical parametric resonant cavity comprises the OPO input mirror 7 and the OPO output mirror 9, facilitating oscillation of the signal light in the cavity and transmission of the short-wave infrared idler light; the nonlinear crystal 8 meets the phase matching condition of parametric oscillation, realizing efficient energy conversion and short-wave infrared tuning output, and the included angle θ between the axis of the nonlinear crystal 8 and the pump beam is variable; the filter 10 is arranged behind the OPO output mirror 9, and the light transmission surface of the filter 10 is at a certain inclination angle with the pump output beam, so that the pump light is reflected at a certain inclination angle, and the light transmitted through the filter 10 is all short-wave infrared light; the fixed right-angle prism 11 and the movable right-angle prism 12 are placed reversely, with their inclined surfaces parallel, forming a parallel refractive structure. By adjusting the lateral position of the movable right-angle prism 12 perpendicular to the direction of the idler light, the relative position L between the movable right-angle prism 12 and the fixed right-angle prism 11 is changed, and the effective thickness of the refractive structure is changed, so that the refractive effect compensates for the lateral displacement of the output beam caused by the large-angle rotation of the nonlinear crystal 8, keeping the position of the output beam stable and unchanged.

[0033] As shown, by rotating the nonlinear crystal 8, the phase matching angle θ is changed, and the output wavelength of the short-wave infrared light source is adjusted. Figure 3

[0034] Device working principle:

[0035] Step 1: Pre-calibrate the relationship model between the included angle θ and the distance L: L = -0.00434 × (θ 3 ) + 0.30402 × (θ 2 ) - 14.06119 × θ + 1355.17902, which is used to compensate for the displacement of the output direction of the short-wave infrared idler light beam caused by the rotation of the nonlinear crystal 8 during the tuning process;

[0036] ​Step 2: Adjust and real-time detect the angle θ between the axis of the nonlinear crystal 8 and the pump beam;

[0037] Step 3: Calculate the following distance L corresponding to the current angle θ according to the relationship model;

[0038] Step 4: Adjust the transverse relative position distance L between the moving right-angle prism 12 and the fixed right-angle prism 11 along the idler beam direction to the value calculated in step 3, so as to change 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 moving right-angle prism 8), compensate for the transverse displacement deviation of the output direction of the mid-long wave infrared idler beam caused by the large rotation angle of the nonlinear crystal 8 in the tuning process, and realize the beam pointing stability.

[0039] Embodiment 1:

[0040] Further, the artificial manual adjustment of embodiment 1 can be adopted: in step 2, the angle θ between the axis of the nonlinear crystal 8 and the pump beam is manually adjusted; and in step 4, the distance L between the moving right-angle prism 11 and the fixed right-angle prism 12 is manually adjusted.

[0041] Embodiment 2:

[0042] Further, on the basis of the device of embodiment 1, the automatic adjustment of embodiment 2 can also be obtained by setting a moving device, as shown in Figure 2 The nonlinear crystal 8 is arranged on a rotary table, and the rotary table is connected to a host computer. The moving right-angle prism 12 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. A program module is arranged in the host computer, and when the program is executed, the rotary table and the one-dimensional linear motion module are outputted with instructions to realize the following flow steps, as shown in Figure 3

[0043] Step S1: Pre-calibrate the relationship model between the angle θ and the distance L: L = -0.00434 × (θ 3 )+0.30402 × (θ 2 )-14.06119 × θ+1355.17902, which is used to compensate for the displacement of the output direction of the mid-long wave infrared idler beam caused by the rotation of the nonlinear crystal 8 in the tuning process;

[0044] Step S2: The rotary table feeds back the angle, and the angle θ between the axis of the nonlinear crystal 8 and the pump beam is displayed in real time through the computer rotary table program interface;

[0045] Step S3: Calculate the following distance L corresponding to the current angle θ according to the relationship model;

[0046] ​Step S4: control the motor rotation on the one-dimensional linear motion module, drive the moving right-angle prism 12 to adjust its relative position L with the fixed right-angle prism 11 along the direction of the middle-long wave infrared idler light, so as to change the effective thickness of the refractive structure, compensate the transverse displacement deviation of the output direction of the middle-long wave infrared idler light beam caused by the large rotation angle of the nonlinear crystal 8 in the tuning process, and realize the light beam pointing stability.

[0047] In practical application, the pump laser 1 is a commercial neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, and the output pump laser wavelength is 1.064 μm. The magneto-optical isolator 2 is a spatial optical isolator, which is coated with a 1.064 μm antireflection film to ensure one-way transmission of the pump laser and avoid return light from causing laser damage. The convex lens 3 and the concave lens 4 are coaxial with the pump laser beam, and the concave lens 4 is arranged at the focal point of the convex lens 3 to improve the energy density of the light beam. The first 45° mirror 5 and the second 45° mirror 6 are used to reflect the pump laser, so that the optical path structure is more compact. The pump laser enters the nonlinear crystal 8 through the OPO input mirror 7, and by rotating the nonlinear crystal 8, the phase matching condition is changed to generate tunable short-wave infrared laser, which is then output by the OPO output mirror 9. The OPO input mirror 7 is a plane mirror made of K9 glass, and the incident surface is coated with a 1.064 μm pump light antireflection film, and the outgoing surface is coated with a 1.6-3.2 μm light high-reflection film. The OPO output mirror 9 is a plane mirror made of CaF2, and the incident surface is coated with a pump light high-transmission, signal light high-reflection and short-wave infrared light high-transmission film, and the outgoing surface is coated with a pump light high-transmission and short-wave infrared high-transmission film. In actual operation, the OPO output mirror 9 is divided into two groups, when outputting 1.6-2.1 μm short-wave infrared light, the mirror is coated with a pump light high-transmission, 1.6-2.1 μm idler light high-transmission and 2.2-3.2 μm signal light high-reflection film on the incident surface, and a pump light high-transmission and idler light high-transmission film on the outgoing surface; when outputting 2.2-3.2 μm short-wave infrared light, the mirror is coated with a pump light high-transmission, 1.6-2.1 μm signal light high-reflection and 2.2-3.2 μm idler light high-transmission film on the incident surface, and a pump light high-transmission and idler light high-transmission film on the outgoing surface. The nonlinear crystal 8 is a potassium titanyl phosphate crystal with a light transmission surface size of 15×7 mm2, which is coated with a 1.06 μm and a 1.6-3.2 μm antireflection film, and has a length of 20 mm. The crystal has a large second-order nonlinear coefficient and a high damage threshold, and the dielectric properties of the crystal ensure the phase matching of the parametric oscillation process, which is conducive to realizing efficient energy conversion and short-wave infrared light output, and the wavelength tuning is realized by rotating the nonlinear crystal. The filter 10 is made of CaF2, and the surface is coated with a pump light high-reflection film and a 1.6-3.2 μm short-wave infrared light antireflection film, which is used to filter out the remaining pump light, so that all the light transmitted through the filter 10 is short-wave infrared light. The fixed right-angle prism 11 and the displacement right-angle prism 12 are both straight prisms with an isosceles right-angle triangle as the base surface, and the right-angle side length is 25 mm and the height is 25 mm. The material is CaF2, and the surface is coated with a 1.6-3.2 μm short-wave infrared light antireflection film to reduce the reflection loss of the short-wave infrared light.

[0048] The above-mentioned device for compensating for the light beam deviation caused by short-wave infrared tuning by translating the right-angle prism is suitable for application researches such as spectral analysis, remote sensing and imaging, and has the advantages of simple structure, easy operation and better meeting the needs of practical application.

Claims

1. A large-angle tuned shortwave infrared coherent light source with stable beam pointing, characterized in that: The system includes a pump laser (1), a magneto-optical isolator (2), a convex lens (3), a concave lens (4), an OPO input mirror (7), a nonlinear crystal (8), an OPO output mirror (9), a filter (10), a fixed right-angle prism (11), and a movable right-angle prism (12), arranged sequentially along the output direction of the pump source. The pump laser (1) emits a pump beam. The magneto-optical isolator (2) enables unidirectional transmission of the pump beam. The axes of the convex lens (3) and the concave lens (4) coincide with the pump laser beam, and the concave lens (4) is located at the focal point of the convex lens (3). The optical parametric oscillator includes a resonant cavity composed of the OPO input mirror (7) and the OPO output mirror (9), and a nonlinear crystal (8) within the resonant cavity. The angle θ between the central axis of the nonlinear crystal (8) and the pump beam is variable. The resonant cavity is used to cause the input pump beam to undergo frequency down-conversion under the action of the nonlinear crystal (8) within the cavity, generating a frequency of 1.6-3.

2. The OPO output mirror (9) outputs the residual pump light and idler light, which are short-wave infrared signal light and idler light with a wavelength of μm. The filter (10) is used to reflect the residual pump light and transmit short-wave infrared light. The fixed right-angle prism (11) and the movable right-angle prism (12) are placed in reverse with parallel inclined planes to form a parallel refraction structure. The lateral relative position of the movable right-angle prism (12) and the fixed right-angle prism (11) is variable to change the effective thickness of the refraction structure. The nonlinear crystal (8) is a potassium titanate oxyarsenate crystal; the nonlinear crystal (8) is placed on a horizontal turntable, and the rotation of the turntable changes the angle θ between the central axis of the nonlinear crystal (8) and the pump beam; The movable right-angle prism (12) is set on a horizontal one-dimensional linear displacement stage, and its relative position L with the fixed right-angle prism (11) can be adjusted along the direction perpendicular to the idler light, thereby changing the effective thickness of the refractive structure and compensating for the lateral displacement deviation of the output direction of the short-wave infrared idler light beam caused by the rotation of the nonlinear crystal (8) during the tuning process.

2. The large-angle tuned shortwave infrared coherent light source with stable beam pointing according to claim 1, characterized in that, The pump laser (1) is a neodymium-doped yttrium aluminum garnet laser with an output pump laser wavelength of 1.064 μm; the magneto-optical isolator (2) is a spatial optical isolator coated with a 1.064 μm antireflection film.

3. The large-angle tuned short-wave infrared coherent light source with stable beam pointing according to claim 1, characterized in that, Also includes: A first 45° reflector (5) and a second 45° reflector (6) are set between the concave lens (4) and the OPO input mirror (7) to reflect the pump light and change the direction of the light path.

4. The large-angle tuned shortwave infrared coherent light source with stable beam pointing according to claim 1, characterized in that, The OPO input mirror (7) is a plane mirror made of 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 (9) is a plane mirror made of CaF2. The incident surface is coated with a pump light high-transmittance film, a signal light high-reflection film, and an idler light high-transmittance film, and the output surface is coated with a pump light high-transmittance film and an idler light high-transmittance film.

5. A large-angle tuned short-wave infrared coherent light source with stable beam pointing according to claim 1, characterized in that, The filter (10) is made of CaF2 and has a pump light high reflectivity film and a 1.6-3.2 μm short-wave infrared light anti-reflection film on its surface.

6. The large-angle tuned shortwave infrared coherent light source with stable beam pointing according to claim 1, characterized in that, The fixed right-angle prism (11) and the movable right-angle prism (12) are both right triangular prisms with isosceles right triangles as their bases, made of CaF2, and coated with a 1.6-3.2 μm short-wave infrared anti-reflection film.

7. The beam-direction-stable, large-angle-tuned, medium-long-wave infrared coherent light source device according to claim 1, characterized in that, It also includes a host computer, which is connected to the horizontal turntable below the pump laser (1), the magneto-optical isolator (2), the nonlinear crystal (8), and the one-dimensional linear displacement stage below the movable right-angle prism (12), and is used to output command signals to control the operation of each device.

8. A method for controlling a large-angle tuned medium-long-wave infrared coherent light source with stable beam pointing, based on the large-angle tuned short-wave infrared coherent light source with stable beam pointing as described in claim 1, characterized in that... Includes the following steps: Step 1: Pre-determine the relationship model between the included angle θ and the distance L: Where A, B, C, and D are model coefficients that have been pre-calibrated multiple times; Step 2: Adjust and detect in real time the angle θ between the central axis of the nonlinear crystal (8) and the pump beam; Step 3: Based on the relationship model, calculate the lateral relative position distance L corresponding to the current included angle θ; Step 4: Adjust the lateral relative position distance L between the movable right-angle prism (12) and the fixed right-angle prism (11) along the idler beam direction to the value calculated in step 3. This is used to change the effective thickness of the refractive structure, compensate for the lateral displacement deviation in the output direction of the mid-to-long-wave infrared idler beam caused by the large rotation angle of the nonlinear crystal (8) during the tuning process, and achieve beam pointing stability.

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