Mid-infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator

Abstract

The application relates to a middle wave infrared coherent light source based on a 90-degree-rotated four-mirror non-planar annular resonant cavity, which comprises a pump laser, a beam-reducing lens group, a magneto-optical isolator, a half-wave plate, a 45-degree mirror, a polarization cube, a 45-degree mirror, a four-mirror non-planar annular resonant cavity and a filter. The pump laser is used for generating 1.064 mu m laser; the beam-reducing lens group is used for improving the energy density of a light beam; the magneto-optical isolator is used for ensuring one-way transmission of laser; the half-wave plate is used for adjusting the polarization state of pump light; the 45-degree mirror is used for folding an optical path; the polarization cube is used for reflecting horizontally polarized pump light; the four-mirror non-planar annular resonant cavity is used for generating middle wave infrared light; an input mirror, two signal light reflecting mirrors and an output mirror constitute an overall cavity type; and the filter is used for blocking pump light. Through the annular cavity structure, the application forms a highly central-symmetrical laser mode output by multiple image rotations of signal light, and realizes middle infrared high-beam-quality laser output.

Description

Technical Field

[0001] This invention relates to the field of infrared optics technology, specifically to a mid-wave infrared coherent light source based on a four-mirror non-planar ring resonator with an image rotated 90°. Background Technology

[0002] Since the advent of lasers, their outstanding performance in directionality, monochromaticity, and coherence has led to the rapid development of laser technology, resulting in its wide application in defense, medicine, and communications. Mid-wave infrared lasers have extensive applications in research fields such as spectral analysis, remote sensing, and imaging. Traditional planar parallel cavities are limited by the optical damage threshold and the need to shorten the cavity length to achieve high efficiency. Increasing the spot size or reducing the cavity length to improve efficiency will increase the Fresnel number of the resonant cavity, i.e., increase diffraction loss and reduce beam quality.

[0003] Traditional planar parallel cavities require high precision in adjustment, and their stability lies between that of stable and unstable cavities, resulting in significant diffraction and geometric losses. Currently, mid-wave infrared coherent light sources based on planar parallel cavities have high beam quality factors but poor beam quality. Furthermore, as a critical cavity, the parallel planar cavity is highly sensitive to disturbances in the collimation angle of the cavity mirror, making it prone to detuning during laser output and further affecting the quality of the laser output. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a mid-wave infrared coherent light source based on a four-mirror non-planar ring resonator with a 90° image rotation. The resonant light oscillates through multiple unidirectional reflections within the four non-planar mirrors. Since there is an angle between the planes formed by beam reflections between adjacent mirrors, this is the image rotation angle. Consequently, the signal light undergoes image and polarization direction rotation after reflection. By designing the image rotation angle between the mirrors and the total image rotation angle, and by inserting a half-wave plate within the cavity to control the polarization direction of the parametric light, the parametric light, after reflection and re-passing through the nonlinear crystal, can maintain its polarization direction, thus creating parametric light gain. Simultaneously, at a specific image rotation angle, the parametric light undergoes multiple image rotations to form a highly centrosymmetric laser mode output, achieving high beam quality laser output for mid-infrared OPO.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0006] A mid-wave infrared coherent light source based on a 90° rotated four-mirror non-planar ring resonator includes: a pump laser and a magneto-optical isolator, a first half-wave plate, a polarization cube, a non-planar ring resonator, and a filter arranged sequentially on the pump optical path of its output.

[0007] The magneto-optical isolator is used to enable unidirectional transmission of the pump light;

[0008] The first half-wave plate is used to adjust the polarization state of the pump light;

[0009] The polarization cube is used to reflect the component of the polarization pump light in the set direction;

[0010] The non-planar ring resonator is used to generate signal light after the input polarized pump light is acted upon by the internal nonlinear crystal. The signal light is then iteratively reflected by the non-planar ring resonator and output as mid-infrared idler light by the nonlinear crystal.

[0011] The filter is used to reflect the pump light and output mid-infrared idler light.

[0012] The nonplanar ring resonant cavity includes: an OPO input mirror, a first signal light reflector, a nonlinear crystal, a second signal light reflector, a second half-wave plate, and an OPO output mirror; the nonlinear crystal undergoes frequency down-conversion under the action of pump light, generating a signal light with a wavelength of 1.38μm and a mid-infrared idler light with a wavelength of 4.66μm; the OPO input mirror, the OPO output mirror, and the two signal light reflectors cause the signal light to oscillate within the cavity, and the second half-wave plate keeps the polarization state of the signal light unchanged;

[0013] The pump light optical path consists of: an OPO input mirror, a nonlinear crystal, and an OPO output mirror.

[0014] The optical path of the signal light is: OPO input mirror, OPO output mirror, second signal light reflector, first signal light reflector, and OPO input mirror;

[0015] The mid-infrared idler light optical path is: nonlinear crystal, OPO output mirror.

[0016] The nonlinear crystal is a selenium-potassium-barium crystal.

[0017] The OPO input mirror is a plane mirror made of K9 glass, with an anti-reflection coating for pump light on the incident surface and an anti-reflection coating for pump light and a high-reflection coating for signal light on the output surface; the OPO output mirror is a plane mirror made of CaF2, with a high-transmittance coating for pump light, a high-reflection coating for signal light, and a high-transmittance coating for idler light on the incident surface, and a high-transmittance coating for pump light and an high-transmittance coating for idler light on the output surface.

[0018] The first signal light reflector is a plane mirror, and the second signal light reflector is also a plane mirror. Both are made of CaF2, and their inner surfaces are coated with a high-reflectivity film for signal light.

[0019] The second half-wave plate is a 1.38μm half-wave plate, used to adjust the polarization state of the signal light.

[0020] A convex lens and a concave lens are sequentially arranged in the optical path between the pump laser and the magneto-optical isolator. The light-transmitting surface of the convex lens is perpendicular to the pump optical path. The surface of the convex lens is coated with a near-infrared anti-reflection film to improve the beam energy density.

[0021] It also includes a first 45° reflector and a second 45° reflector respectively set in front of and behind the polarization cube to reflect pump light, and the folded pump light path makes the light source structure compact; the polarization cube is made of K9 glass, with near-infrared anti-reflection coatings on the four incident surfaces and near-infrared polarization coatings on the inclined surfaces to reflect horizontally polarized pump light.

[0022] The pump laser is a commercial neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, which generates 1.064 μm pump light; the half-wave plate is a 1.064 μm half-wave plate used to adjust the polarization state of the pump light.

[0023] The filter is used to block the remaining pump light and output 4.66μm mid-wave infrared light. It is made of CaF2 and its surface is coated with a pump light high-reflection film and a 4.66μm mid-wave infrared light anti-reflection film.

[0024] The present invention has the following beneficial effects and advantages:

[0025] 1. Since the annular OPO is unidirectional, it avoids high irradiance at the antinodes of the standing wave, reducing the possibility of damage to the OPO mirror and crystal optics.

[0026] 2. In four consecutive cavity passes, the off-axis rays in the signal beam sample four different parts of the pump light.

[0027] 3. This invention utilizes a four-mirror non-planar ring structure to perform multiple image rotations on the signal light to form a highly centrally symmetrical laser mode output, thereby achieving high beam quality laser output in the mid-infrared region.

[0028] 4. Compared with the traditional planar parallel cavity, the four-mirror non-planar ring resonator of the present invention is no longer limited by the optical damage threshold and the reduction of beam quality due to the use of short cavities to achieve high efficiency, while having the advantage of achieving high-efficiency and high-quality beam output. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a high-quality mid-wave infrared coherent light source based on a four-mirror non-planar ring resonator with an image rotated 90°, provided by the present invention.

[0030] In this array, 1 is the pump laser, 2 is the convex lens, 3 is the concave lens, 4 is the magneto-optical isolator, 5 is the first half-wave plate, 6 is the first 45° reflector, 7 is the polarization cube, 8 is the second 45° reflector, 9 is the OPO input mirror, 10 is the first signal light reflector, 11 is the nonlinear crystal, 12 is the second signal light reflector, 13 is the second half-wave plate, 14 is the OPO output mirror, and 15 is the filter. Detailed Implementation

[0031] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough 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 modifications without departing from the spirit of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0032] 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 this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0033] like Figure 1 As shown, the present invention provides a high-quality mid-wave infrared coherent light source based on a four-mirror non-planar ring resonator with a 90° rotating image, comprising a pump laser 1, a convex lens 2, a concave lens 3, a magneto-optical isolator 4, a first half-wave plate 5, a first 45° reflector 6, a polarization cube 7, a second 45° reflector 8, an OPO input mirror 9, a first signal light reflector 10, a nonlinear crystal 11, a second signal light reflector 12, second half-wave plates 13 and 14 being OPO output mirrors, and a filter 15.

[0034] The pump laser 1 generates a pump laser for OPO, and the pump light passes sequentially through a convex lens 2, a concave lens 3, a magneto-optical isolator 4, a first half-wave plate 5, a first 45° reflector 6, a polarization cube 7, a second 45° reflector 8, an OPO input mirror 9, a nonlinear crystal 11, an OPO output mirror 14, and a filter 15.

[0035] The axes of the convex lens 2 and the concave lens 3 coincide with the pump laser beam to increase the beam energy density; the magneto-optical isolator 4 ensures unidirectional transmission of the pump light and avoids damage to the laser caused by the return light; the first half-wave plate 5 is used to adjust the polarization state of the pump light; the first 45° reflector 6 is used to reflect the pump light, making the structure more compact; the polarization cube 7 is used to reflect the horizontally polarized pump light and forms a pump energy control system with the first half-wave plate 5, which facilitates the adjustment of the pump energy; the second 45° reflector 8 is used to reflect the pump light.

[0036] The four-mirror non-planar ring resonator with a 90° rotation includes an OPO input mirror 9, a first signal light reflector 10, a nonlinear crystal 11, a second signal light reflector 12, a second half-wave plate 13, and an OPO output mirror 14. Under the action of the pump light, the nonlinear crystal 11 undergoes frequency down-conversion, generating a signal light with a wavelength of 1.38 μm and an idler light with a wavelength of 4.66 μm. The OPO input mirror 9, the OPO output mirror 14, and the two signal light reflectors 10 and 12 cause the signal light to oscillate within the cavity. The half-wave plate 13 keeps the polarization state of the rotated signal light unchanged. The optical path of the pump light within the cavity is: OPO input mirror (9), nonlinear crystal (11), OPO output mirror (14). The optical path of the signal light within the cavity for four consecutive iterations is: OPO input mirror (9), OPO output mirror (14), second signal light reflector (12), first signal light reflector (10), OPO input mirror (9), and so on. The optical path of the mid-infrared idler light inside the cavity is: nonlinear crystal (11) and OPO output mirror (14).

[0037] The nonlinear crystal 11 satisfies the phase matching condition of parametric oscillation, achieving efficient energy conversion and mid-wave infrared light output under normal incidence. The filter 15 is set behind the OPO output mirror 14, and its light-transmitting surface is tilted at a certain angle to the pump output beam, so that the pump light is reflected at a certain tilt angle, and all the light passing through the filter 15 is mid-wave infrared light.

[0038] In practical applications, pump laser 1 is a commercially available neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, with an output pump laser wavelength of 1.064 μm. Convex lens 2 and concave lens 3 are made of K9 glass, with a near-infrared anti-reflection coating on the convex lens surface. The axes of convex lens 2 and concave lens 3 coincide with the pump laser beam, effectively constricting the pump light to increase beam energy density. Magneto-optical isolator 4 is a spatial optical isolator, coated with a 1.064 μm anti-reflection coating to ensure unidirectional transmission of the pump laser and prevent damage to the laser from reflected light. The first half-wave plate 5 is made of quartz crystal, coated with a 1.064 μm anti-reflection coating, used to adjust the polarization state of the pump light. The first 45° reflector 6 is made of K9 glass, coated with a 1.064 μm high-reflection coating, used to reflect the pump laser, making the optical path structure more compact. The polarization cube 7 is made of K9 glass, with near-infrared anti-reflection coatings on its four incident surfaces and near-infrared polarization coatings on its inclined surfaces. The pump laser is reflected by polarization cube 7 to select the horizontal polarization component, ensuring that the polarization state entering the cavity after reflection by the second reflecting mirror 8 is horizontal. The pump light enters the nonlinear crystal 11 through the OPO input mirror 9 and is then output by the OPO output mirror 14. The OPO input mirror 9 is a plane mirror made of K9 glass, with a 1.064μm pump light anti-reflection coating on its incident surface and a 1.37μm high-reflection coating on its output surface. The first signal light high-reflection mirror 10 and the inner surface of the cavity are coated with a 1.37μm high-reflection coating, and the half-wave plate 13 is coated with a 1.37μm anti-reflection coating to adjust the polarization state of the signal light. The OPO output mirror 14 is a plane mirror made of CaF2, with pump light high-transmittance, signal light high-reflection, and short-wave infrared high-transmittance coatings on its incident surface and pump light high-transmittance and mid-wave infrared high-transmittance coatings on its output surface. Nonlinear crystal 11 is a selenium-potassium-barium crystal with dimensions of 7×10×15mm. 3 The crystal is coated with 1.06μm and 1.6-3.2μm antireflection films. This crystal has a large second-order nonlinear coefficient and a high damage threshold, which is beneficial for achieving efficient energy conversion and mid-wave infrared light output. Filter 15 is made of CaF2 and is coated with a pump light high-reflection film and a 4.6μm mid-wave infrared antireflection film to filter out the remaining pump light, ensuring that all light passing through filter 15 is mid-wave infrared light.

[0039] The aforementioned high-quality mid-wave infrared coherent light source based on a four-mirror non-planar ring resonator with an image rotation of 90° is suitable for generating coherent mid-wave infrared light sources with high beam quality and high conversion efficiency, and can better meet the needs of practical applications.

[0040] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should be considered within the scope of protection of the present invention.

Claims

1. A mid-infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator, characterized in that, The application relates to a pump laser (1) and a magnetic-optical isolator (4), a first half-wave plate (5), a polarization cube (7), a non-planar ring resonator and a filter (15) arranged in sequence on the pump light path of the output of the pump laser; the magnetic-optical isolator (4) is used for making the pump light unidirectional transmission; the first half-wave plate (5) is used for adjusting the polarization state of the pump light; the polarization cube (7) is used for reflecting the set direction component of the polarized pump light; the non-planar ring resonator is used for making the input polarized pump light generate signal light after the action of an internal nonlinear crystal (11), and the signal light generates middle infrared idler light output after the iteration reflection of the non-planar ring resonator and the nonlinear crystal (11); and the filter (15) is used for reflecting the pump light and outputting the middle infrared idler light. The non-planar ring resonator comprises an OPO input mirror (9), a first signal light reflecting mirror (10), the nonlinear crystal (11), a second signal light reflecting mirror (12), a second half-wave plate (13) and an OPO output mirror (14); the nonlinear crystal (11) generates signal light with a wavelength of 1.38 mu m and 4.66 mu m middle infrared idler light under the action of the pump light; the OPO input mirror (9), the OPO output mirror (14) and the two signal light reflecting mirrors (10 and 12) make the signal light oscillate in the cavity, and the second half-wave plate (13) keeps the polarization state of the signal light unchanged. The pump light path is: the OPO input mirror (9), the nonlinear crystal (11) and the OPO output mirror (14). The signal light path is: the OPO input mirror (9), the OPO output mirror (14), the second signal light reflecting mirror (12), the first signal light reflecting mirror (10) and the OPO input mirror (9). The middle infrared idler light path is: the nonlinear crystal (11) and the OPO output mirror (14). The nonlinear crystal (11) is a BaGa4Se7 crystal.

2. The mid-wave infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator according to claim 1, characterized in that, The OPO input mirror (9) is a plane mirror, the material is K9 glass, the incident surface is coated with a pump light anti-reflection film, and the emitting surface is coated with a pump light anti-reflection film and a signal light high-reflection film; the OPO output mirror (14) is a plane mirror, the material is CaF2, the incident surface is coated with a pump light high-transmission film, a signal light high-reflection film and an idler light high-transmission film, and the emitting surface is coated with a pump light high-transmission film and an idler light high-transmission film.

3. The mid-wave infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator according to claim 1, characterized in that, The first signal light reflecting mirror (10) and the second signal light reflecting mirror (12) are plane mirrors, the material is CaF2, and the cavity surfaces are coated with a signal light high-reflection film.

4. The mid-wave infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator according to claim 1, characterized in that, The second half-wave plate (13) is a 1.38 mu m half-wave plate and is used for adjusting the polarization state of the signal light.

5. The mid-wave infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator according to claim 1, characterized in that, A convex lens (2) and a concave lens (3) are further arranged in sequence on the light path between the pump laser (1) and the magnetic-optical isolator (4), the light transmission surfaces of the convex lens (2) and the concave lens (3) are perpendicular to the pump light path, the surface of the convex lens (2) is coated with a near-infrared anti-reflection film, and the convex lens (2) is used for improving the beam energy density.

6. The mid-wave infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator according to claim 1, characterized in that, ​ 7. The mid-wave infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator according to claim 1, characterized in that, Also included are a first 45° mirror (6) and a second 45° mirror (8) respectively arranged in front of and behind the polarization cube (7) for reflecting the pump light and folding the pump light path to make the light source structure compact; the polarization cube (7) is made of K9 glass, four incident surfaces of which are coated with near-infrared antireflection film, and the inclined surface is coated with near-infrared polarizing film for reflecting horizontally polarized pump light.

8. The mid-infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator according to any one of claims 1-7, characterized in that, The pump laser (1) is a commercial neodymium-doped yttrium aluminum garnet (Nd:YAG) laser for generating 1.064 μm pump light; the first half-wave plate (5) is a 1.064 μm half-wave plate for adjusting the polarization state of the pump light.

9. The mid-infrared coherent light source based on a 90°-rotated four-mirror non-planar ring resonator according to any one of claims 1-7, characterized in that, The filter (15) is used for blocking the remaining pump light and outputting 4.66 μm mid-wave infrared light, and is made of CaF2 and coated with pump light high-reflection film and 4.66 μm mid-wave infrared light antireflection film on the surface.

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