A high-extinction-ratio double-longitudinal-mode output thermal frequency stabilized helium-neon laser

Abstract

A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output belongs to the field of laser application technology. This invention addresses the problem of fabricating a helium-neon laser that is easy to assemble and integrate while withstanding large temperature differences. The invention involves connecting a platinum resistance temperature sensor to the central surface of a dual longitudinal mode helium-neon laser tube. A heating film is attached to the outer wall of the laser tube. The orthogonal dual longitudinal mode laser emitted by the laser tube is perpendicularly incident on the first beam splitter in the longitudinal mode separation optical path of a birefringent crystal. The first and second refracted beams propagate to the second and third beam splitters, respectively. A first photodetector is positioned in the optical path of the reflected light from the second beam splitter, and a second photodetector is positioned in the optical path of the reflected light from the third beam splitter. The frequency stabilization control circuit module receives feedback signals from the platinum resistance temperature sensor, the first photodetector, and the second photodetector, driving and controlling the current in the heating film of the helium-neon laser tube.

Description

Technical Field

[0001] This invention belongs to the field of laser application technology, specifically relating to a thermally stable helium-neon laser with high extinction ratio and dual longitudinal mode output. Background Technology

[0002] Thermal frequency stabilization technology for dual-mode helium-neon lasers is a general technique for achieving high-precision frequency stabilization of dual-frequency helium-neon lasers. This technology adjusts the resonant cavity length to symmetrically distribute two adjacent orthogonal longitudinal modes on either side of the gain curve center and implements closed-loop feedback control. Due to its all-optical passive frequency stabilization and high stabilization accuracy, this technology is widely used in key fields such as precision laser interferometry. In practical applications of multi-axis precision measurement, it is often necessary to perform high-purity separation of the two longitudinal modes output from the helium-neon laser, which have different frequencies and orthogonal polarization directions, to produce two high-extinction-ratio linearly polarized beams for use in subsequent multi-axis interferometers and other measurement modules. This places extremely high demands on the extinction ratios of the two longitudinal modes output from the frequency-stabilized helium-neon laser.

[0003] However, the current mainstream longitudinal mode separation optical path in frequency-stabilized helium-neon lasers has a fundamental physical limitation in simultaneously acquiring two high-purity orthogonal longitudinal modes. The traditional optical path mainly selects a polarization beam splitter (PBS) to separate the two longitudinal modes output by the helium-neon laser. The PBS is usually formed by cementing two right-angle prisms together, and the cemented surface is coated with multiple layers of high and low refractive index films. Although the PBS can perfectly separate p-light and s-light with extremely high extinction ratio under ideal conditions, in actual processing, the refractive index of the cemented layer is not perfectly matched with the substrate, which will produce additional Fresnel reflection. Moreover, the high-stress refractive film layer will also cause a small deformation of the prism substrate after coating, introducing stress birefringence and changing the polarization state of the incident light (Chen Hongfang, Ding Xuemei, Zhong Zhi. Effect of nonlinearity by the nonideal splitting performance of polarization beam splitter in laser heterodyne interferometry[J]. Chinese JLasers, 2006, 33(11): 1562-1566.). This non-ideal characteristic results in a significantly higher extinction ratio for transmitted light compared to reflected light when separated by a PBS (Bipolar Separator). Therefore, in practical applications, frequency-stabilized helium-neon lasers using traditional separation paths often only utilize the transmitted light to obtain high-extinction-ratio polarized light, meaning they output only light of a single frequency and polarization direction. The other orthogonal longitudinal mode in the reflected direction cannot be utilized for subsequent high-precision measurements due to severe polarization leakage. This asymmetry in device performance prevents frequency-stabilized helium-neon lasers using traditional PBS separation paths from simultaneously outputting two high-extinction-ratio orthogonal longitudinal modes, failing to meet the demands of multi-axis precision measurement and other similar applications. Therefore, there is an urgent need for a frequency-stabilized helium-neon laser capable of simultaneously outputting two high-extinction-ratio orthogonal longitudinal modes to meet the laser source requirements of multi-axis precision measurement and other similar scenarios.

[0004] To improve the extinction ratio of the longitudinal mode separation optical path in a frequency-stabilized helium-neon laser, some schemes use a Wollaston prism (WP) made of cemented calcite right-angle prisms for beam splitting. The WP does not require coating at the cemented joint, thus its extinction ratio is significantly better than that of the PBS when used for beam splitting. However, the two output beams separated by the WP naturally have a certain tilt angle, making it impossible to maintain horizontal parallel output (Yang Hongxing, Wang Yan, Yin Ziqi, et al. Design of a high frequency accuracy heterodyne lasersource working in a wide temperature range[J].Chinese Optics Letters,2024,22(4):88-93.). This inherent tilt angle makes it difficult for the frequency-stabilized helium-neon laser to be aligned and adjusted with subsequent external optical measurement modules, severely hindering its integration with subsequent systems. Furthermore, in industrial scenarios with large temperature differences, the internal cemented joints of both the PBS and WP face the risk of failure. Due to the significant difference in the coefficient of thermal expansion (CTE) between the prism substrate material and the adhesive medium under drastic temperature fluctuations, the adhesive interface will generate extremely large internal thermal stress. Long-term operation can easily lead to delamination, blistering, or even failure and cracking of the adhesive layer, which cannot meet the long-term high reliability requirements in industrial scenarios (Fan Zhigang, Chang Hong, Chen Shouqian. Thermal stress and deformation analysis of adhesive optical components [J]. Optical Technology, 2011, 37(3):366-369.).

[0005] In summary, while the traditional dual-mode separation optical path using PBS devices in existing thermally stabilized helium-neon lasers facilitates the arrangement of the laser's output beam direction, the asymmetry in the extinction ratios of the transmitted and reflected beams prevents the simultaneous output of two high-extinction-ratio polarized beams, making it difficult to meet the requirements of multi-axis measurement and other application environments. Birefringent devices naturally possess the advantages of high extinction ratios and symmetry, but when using glued birefringent devices (such as WP) in a dual-mode separation optical path, the actual output beam has a tilt angle, significantly increasing the difficulty of assembling and integrating the frequency-stabilized helium-neon laser with subsequent application modules. Furthermore, both of these beam splitting devices suffer from reliability issues due to the easy cracking of the adhesive layer in industrial environments with large temperature differences. Therefore, there is an urgent need for a thermally stabilized helium-neon laser that can simultaneously output two high-extinction-ratio orthogonal longitudinal modes, maintain a horizontal output beam direction for ease of subsequent module assembly and integration, and operate stably in industrial environments with large temperature differences. Summary of the Invention

[0006] The problem to be solved by this invention is to prepare a helium-neon laser that is easy to assemble and integrate and can withstand large temperature differences. A thermally stable helium-neon laser with high extinction ratio and dual longitudinal mode output is proposed.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output includes a dual longitudinal mode helium-neon laser tube, a platinum resistance temperature sensor, a heating film for the helium-neon laser tube, a birefringent crystal longitudinal mode separation optical path, a frequency stabilization control circuit module, a first photodetector, and a second photodetector; the birefringent crystal longitudinal mode separation optical path includes a first beam splitter, a second beam splitter, and a third beam splitter.

[0009] A platinum resistance temperature sensor is connected to the middle surface of the dual-longitudinal-mode helium-neon laser tube. A helium-neon laser tube heating film is attached to the outer wall of the dual-longitudinal-mode helium-neon laser tube. The orthogonal dual-longitudinal-mode laser emitted by the dual-longitudinal-mode helium-neon laser tube is incident perpendicularly on the first beam splitter in the longitudinal mode separation optical path of the birefringent crystal. The first refracted light and the second refracted light propagate to the second beam splitter and the third beam splitter, respectively. A first photodetector is set in the optical path of the reflected light from the second beam splitter, and a second photodetector is set in the optical path of the reflected light from the third beam splitter. The frequency stabilization control circuit module receives feedback signals from the platinum resistance temperature sensor, the first photodetector, and the second photodetector, and drives and controls the current in the heating film of the helium-neon laser tube.

[0010] Furthermore, the first beam splitter is a uniaxial birefringent crystal wedge with a right-angled trapezoidal cross-section and a parallelepiped structure. The vertical side of the first beam splitter is the incident end face of the helium-neon laser tube's incident beam, and the trapezoidal wedge surface is the exit slope. The wedge angle of the first beam splitter is set within the following range:

[0011]

[0012] in, The wedge angle of the first beam splitter. Let be the refractive index when the polarization direction is perpendicular to the optical axis of the first beam splitter crystal. is the refractive index when the polarization direction is parallel to the optical axis of the first beam splitter crystal.

[0013] Furthermore, the second and third beam splitters are both uniaxial birefringent crystal wedges that are made by inverting the top and bottom surfaces of the first beam splitter and enlarging or reducing them proportionally. The trapezoidal wedge surfaces of the second and third beam splitters face the trapezoidal wedge surface of the first beam splitter and remain parallel.

[0014] The second beam splitter is set to maintain a horizontal distance of d1 from the first beam splitter; the third beam splitter is set to maintain a horizontal distance of d2 from the first beam splitter.

[0015] The first, second, and third beam splitters are made of the same uniaxial anisotropic crystal, with their optical axes perpendicular to the direction of the incident beam propagation and parallel or perpendicular to the cross-section of the first beam splitter.

[0016] Furthermore, the first refracted light Second refracted light The light beams propagate to the trapezoidal wedge surfaces of the second and third beam splitters, respectively, where they are reflected and refracted. The resulting two reflected beams are the first reflected beam and the third reflected beam. Second reflected light The two refracted beams produced are the first output beams. Second output light The first reflected light and the first output light The frequency corresponds to the first frequency of the output light from the dual-longitudinal-mode helium-neon laser tube, and the second reflected light... Second output light The frequency corresponds to the second frequency of the output light from the dual-longitudinal-mode helium-neon laser tube.

[0017] Furthermore, in order to meet the detection requirements of the frequency stabilization control circuit module, the first refracted light... The reflectivity and refractive index of the trapezoidal wedge surface of the second beam splitter should be similar to those of the second refracted light. The equal wedge angles at the trapezoidal wedge surface of the third beam splitter are set within the range of the first, second, and third beam splitters. Alternatively, a polarization-insensitive micro-reflective film can be deposited on the trapezoidal wedge surfaces of the second and third beam splitters. In this case, the reflected and refracted light intensities in the second and third beam splitters satisfy the following:

[0018] .

[0019] Furthermore, the first output light Second output light Based on the law of refraction and the geometric relationship between prisms, the vertical distance between the prism and the output light of the dual-longitudinal-mode helium-neon laser tube satisfies:

[0020]

[0021] Wherein, H1 is the first output light The distance between the output light from the dual-longitudinal-mode helium-neon laser tube and H2 is the second output light. The distance between the laser beam and the output light from the dual-longitudinal-mode helium-neon laser tube, θ1 is the distance between the laser beam and the output light from the first refracted light. The angle of refraction at the exit surface of the first beam splitter, θ2, is the second refracted light. The angle of refraction at the exit surface of the first beam splitter;

[0022]

[0023] in, For the first refracted light The refractive index in the first beam splitter For the second refracted light The refractive index in the first beam splitter.

[0024] Furthermore, the first output light Second output light The vertical spacing H satisfies:

[0025] .

[0026] Furthermore, the first reflected light Second reflected light The signals are input into the first photodetector and the second photodetector respectively to obtain the first feedback signal I1 and the second feedback signal I2, which satisfy the following:

[0027]

[0028]

[0029] Where k is the gain of the first photodetector and the second photodetector;

[0030] The frequency stabilization control circuit module detects the first feedback signal I1 and the second feedback signal I2. At this time, the frequency stabilization control circuit module adjusts the heating film of the dual-longitudinal-mode helium-neon laser tube, changes the cavity length of the resonant cavity of the dual-longitudinal-mode helium-neon laser tube, and thus changes the light intensity and frequency of the dual-longitudinal-mode laser until... ,at this time That is, the light intensity of the dual longitudinal mode lasers is equal, and the frequency is stable at a position symmetrical about the center of the gain curve of the helium-neon laser.

[0031] The beneficial effects of this invention are:

[0032] The present invention discloses a thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output. Symmetrically placed birefringent crystal wedges are arranged along the propagation direction of the output longitudinal modes to compensate for the propagation direction of the two refracted beams in the optical path. This ensures that the two output beams propagate parallel in the horizontal direction, facilitating the assembly, adjustment, and integration of the laser with subsequent modules.

[0033] This invention discloses a thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output. Its longitudinal mode separation optical path uses only three crystal wedges to achieve longitudinal mode spatial separation and frequency-stabilized probe beam splitting within a very small common-path space. Compared to helium-neon lasers using traditional PBS or WP beam splitting paths, its size is significantly reduced.

[0034] This invention discloses a thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output. The prisms for the longitudinal mode separation optical path are discrete, non-cemented birefringent crystal wedges, eliminating the need for interface cementing as in traditional beam splitters. This completely avoids polarization leakage caused by cementing stress and interface cracking due to large environmental temperature differences. This ensures both extremely high extinction ratios for the two separated output beams and significantly improves the laser's environmental adaptability under large temperature variations. Attached Figure Description

[0035] Figure 1 This is a simplified structural diagram of a thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output, as described in this invention.

[0036] Figure 2 This is a schematic diagram of the longitudinal mode separation optical path in a thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output, as described in this invention.

[0037] Figure 3 This is a schematic diagram of the physical quantities inside the longitudinal mode separation optical path of a thermally stable helium-neon laser with high extinction ratio dual longitudinal mode output according to the present invention.

[0038] In the figure, 1 is a dual-longitudinal-mode helium-neon laser tube, 2 is a platinum resistance temperature sensor, 3 is a heating film of the dual-longitudinal-mode helium-neon laser tube, 4 is a longitudinal-mode splitting optical path of a birefringent crystal, 5 is a frequency stabilization control circuit module, 6 is a first photodetector, 7 is a second photodetector, 8 is a first beam splitter, 9 is a second beam splitter, and 10 is a third beam splitter. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0040] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0041] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 - Appendix Figure 3 Detailed explanation is as follows:

[0042] Example 1:

[0043] A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output includes a dual longitudinal mode helium-neon laser tube 1, a platinum resistance temperature sensor 2, a helium-neon laser tube heating film 3, a birefringent crystal longitudinal mode separation optical path 4, a frequency stabilization control circuit module 5, a first photodetector 6, and a second photodetector 7; the birefringent crystal longitudinal mode separation optical path 4 includes a first beam splitter 8, a second beam splitter 9, and a third beam splitter 10.

[0044] A platinum resistance temperature sensor 2 is connected to the middle surface of the dual-longitudinal-mode helium-neon laser tube 1. A helium-neon laser tube heating film 3 is attached to the outer wall of the dual-longitudinal-mode helium-neon laser tube 1. The orthogonal dual-longitudinal-mode laser emitted by the dual-longitudinal-mode helium-neon laser tube 1 is perpendicularly incident on the first beam splitter 8 in the longitudinal mode separation optical path 4 of the birefringent crystal. The first refracted light and the second refracted light propagate to the second beam splitter 9 and the third beam splitter 10, respectively. A first photodetector 6 is set in the optical path of the reflected light from the second beam splitter 9, and a second photodetector 7 is set in the optical path of the reflected light from the third beam splitter 10. The frequency stabilization control circuit module 5 receives feedback signals from the platinum resistance temperature sensor 2, the first photodetector 6, and the second photodetector 7, and drives and controls the current in the helium-neon laser tube heating film 3.

[0045] Furthermore, the first beam splitter 8 is a uniaxial birefringent crystal wedge with a right-angled trapezoidal cross-section and a parallelepiped structure. The vertical side of the first beam splitter 8 is the incident end face of the incident beam from the helium-neon laser tube, and the trapezoidal wedge surface is the exit slope. The wedge angle of the first beam splitter 8 is set within the following range:

[0046]

[0047] in, The wedge angle of the first beam splitter 8. The refractive index is the value when the polarization direction is perpendicular to the optical axis of the first beam splitter 8 crystal. is the refractive index when the polarization direction is parallel to the optical axis of the first beam splitter 8 crystal.

[0048] Furthermore, the second beam splitter 9 and the third beam splitter 10 are both single-axis birefringent crystal wedges that are inverted and enlarged or reduced proportionally by the upper and lower bottom surfaces of the first beam splitter 8. The trapezoidal wedge surfaces of the second beam splitter 9 and the third beam splitter 10 are both facing the trapezoidal wedge surface of the first beam splitter 8 and remain parallel.

[0049] The second beam splitter 9 and the first beam splitter 8 are kept at a horizontal distance of d1; the third beam splitter 10 and the first beam splitter 8 are kept at a horizontal distance of d2.

[0050] The first beam splitter 8, the second beam splitter 9, and the third beam splitter 10 are all made of the same uniaxial anisotropic crystal. Their optical axes are perpendicular to the direction of the incident beam propagation and are parallel or perpendicular to the cross-section of the first beam splitter 8.

[0051] Furthermore, the power supply to the dual-longitudinal-mode helium-neon laser tube 1 and the frequency stabilization control circuit module 5 is turned on. The temperature feedback signal of the laser tube 1 is obtained through the platinum resistance temperature sensor 2. After receiving the temperature feedback signal, the frequency stabilization control circuit module 5 drives the heating film 3 of the dual-longitudinal-mode helium-neon laser tube to raise the temperature of the laser tube 1 to near the set temperature value according to the temperature deviation and its rate of change. At this time, the dual-longitudinal-mode helium-neon laser tube 1 emits dual-longitudinal-mode helium-neon laser tube output light containing the first frequency and the second frequency (the polarization directions of the two are orthogonal to each other).

[0052] The output light from the dual-longitudinal-mode helium-neon laser tube propagates horizontally. After being incident perpendicularly on the vertical side of the first beam splitter 8 and transmitted through it, it exits at the inclined surface of the prism. The first and second frequency longitudinal modes within the output light of the dual-longitudinal-mode helium-neon laser tube are spatially deflected and separated into first refracted light with orthogonal polarization directions due to the different refractive indices experienced within the crystal. Second refracted light ;

[0053] Furthermore, the first refracted light Second refracted light The light beams propagate to the trapezoidal wedge surfaces of the second beam splitter 9 and the third beam splitter 10, respectively, where they are reflected and refracted. The resulting two reflected beams are the first reflected beam and the second reflected beam. Second reflected light The two refracted beams produced are the first output beams. Second output light The first reflected light and the first output light The frequency corresponds to the first frequency of the output light from the dual-longitudinal-mode helium-neon laser tube 1, and the second reflected light... Second output light The frequency corresponds to the second frequency of the output light of the dual longitudinal mode helium-neon laser tube 1.

[0054] Furthermore, the first output light Second output light As the final output light of a thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output, its polarization directions are orthogonal to each other. Since the wedge surfaces of the three beam splitters are parallel, the two output beams are restored to parallel horizontal propagation directions at the incident wedge surfaces of the second beam splitter 9 and the third beam splitter 10, respectively, and then emitted. In the vertical direction, the first output light... The spatial height is higher than the second output light ;

[0055] Furthermore, in order to meet the detection requirements of the frequency stabilization control circuit module 5, the first refracted light... The reflectivity and refractive index of the trapezoidal wedge surface of the second beam splitter 9 should be similar to those of the second refracted light. The wedge angles of the first beam splitter 8, the second beam splitter 9, and the third beam splitter 10 are set to be equal at the trapezoidal wedge surface of the third beam splitter 10. Alternatively, a polarization-insensitive micro-reflective film can be deposited on the trapezoidal wedge surfaces of the second beam splitter 9 and the third beam splitter 10. Specifically, the optical path needs to meet one of the following conditions:

[0056] a. The wedge angles of the first beam splitter 8, the second beam splitter 9, and the third beam splitter 10 For a small angle (e.g., 1 degree to 5 degrees), the first refracted light... Second refracted light When the incident angles at the trapezoidal inclined surfaces of the second beam splitter 9 and the third beam splitter 10 approach perpendicular incidence, the difference in natural Fresnel reflectance between the two orthogonally polarized beams approaches zero, and the transmission / reflection ratio can be approximately the same without coating.

[0057] b. A polarization-insensitive micro-reflective film is coated on the trapezoidal wedge surfaces of the second beam splitter 9 and the third beam splitter 10, so that the first refracted light Second refracted light Although the polarization directions are orthogonal, the reflectivity at the wedge surface is strictly equal. Preferably, the polarization-insensitive microreflective film is a multilayer dielectric microreflective film produced by electron beam evaporation or ion-assisted deposition, and the total thickness of the film does not exceed 300 nm, in order to minimize the influence of film stress on the deformation of the crystal substrate. At this time, the reflected and refracted light intensities in the second beam splitter 9 and the third beam splitter 10 satisfy:

[0058] .

[0059] Furthermore, the first output light Second output light Based on the law of refraction and the geometric relationship between prisms, the vertical distance between the prism and the output light of the dual-longitudinal-mode helium-neon laser tube satisfies:

[0060]

[0061] Wherein, H1 is the first output light The distance between the output light from the dual-longitudinal-mode helium-neon laser tube and H2 is the second output light. The distance between the laser beam and the output light from the dual-longitudinal-mode helium-neon laser tube, θ1 is the distance between the laser beam and the output light from the first refracted light. The angle of refraction at the exit surface of the first beam splitter, θ2, is the second refracted light. The angle of refraction at the exit surface of the first beam splitter;

[0062]

[0063] in, For the first refracted light The refractive index in the first beam splitter For the second refracted light The refractive index in the first beam splitter. According to the principle of birefringence in crystals, when... From time to time ,when From time to time ,and , The range of values ​​includes only , There are only two values; no other possible values ​​exist.

[0064] Furthermore, the first output light Second output light The vertical spacing H satisfies:

[0065] .

[0066] Based on the expression for H, it can be seen that in order to make the first output light Second output light To separate the longitudinal modes as much as possible in space and avoid mode competition caused by the superposition of two longitudinal modes in the same physical space, the first beam splitter 8, the second beam splitter 9, and the third beam splitter 10 are selected with small wedge angles and refractive index differences. A crystal with a large uniaxial refractive index anisotropy is used as the crystal material for the first beam splitter 8, the second beam splitter 9, and the third beam splitter 10.

[0067] Furthermore, the first reflected light Second reflected light The signals are respectively input into the first photodetector 6 and the second photodetector 7 to obtain the first feedback signal I1 and the second feedback signal I2, which satisfy the following:

[0068]

[0069]

[0070] Where k is the gain of the first photodetector 6 and the second photodetector 7;

[0071] Based on the frequency stabilization control circuit module 5, the first feedback signal I1 and the second feedback signal I2 are detected, when At the same time, the frequency stabilization control circuit module 5 adjusts the heating film 3 of the dual-longitudinal-mode helium-neon laser tube 1, changes the cavity length of the resonant cavity of the dual-longitudinal-mode helium-neon laser tube 1, and thus changes the light intensity and frequency of the dual-longitudinal-mode laser until... ,at this time That is, the light intensity of the dual longitudinal mode lasers is equal, and the frequency is stable at a position symmetrical about the center of the gain curve of the helium-neon laser.

[0072] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0073] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A thermally stable helium-neon laser with high extinction ratio and dual longitudinal mode output, characterized in that, It includes a dual-longitudinal-mode helium-neon laser tube (1), a platinum resistance temperature sensor (2), a helium-neon laser tube heating film (3), a birefringent crystal longitudinal-mode separation optical path (4), a frequency stabilization control circuit module (5), a first photodetector (6), and a second photodetector (7); the birefringent crystal longitudinal-mode separation optical path (4) includes a first beam splitter (8), a second beam splitter (9), and a third beam splitter (10); A platinum resistance temperature sensor (2) is connected to the middle surface of the dual longitudinal mode helium-neon laser tube (1). A helium-neon laser tube heating film (3) is attached to the outer wall of the dual longitudinal mode helium-neon laser tube (1). The orthogonal dual longitudinal mode laser emitted by the dual longitudinal mode helium-neon laser tube (1) is perpendicularly incident on the first beam splitter (8) in the longitudinal mode separation optical path (4) of the birefringent crystal. The first refracted light and the second refracted light are respectively propagated to the second beam splitter (9) and the third beam splitter (10). The first photodetector (6) is set in the optical path of the reflected light of the second beam splitter (9), and the second photodetector (7) is set in the optical path of the reflected light of the third beam splitter (10). The frequency stabilization control circuit module (5) receives feedback signals from the platinum resistance temperature sensor (2), the first photodetector (6) and the second photodetector (7), and drives and controls the current in the helium-neon laser tube heating film (3).

2. A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output according to claim 1, characterized in that, The first beam splitter (8) is a uniaxial birefringent crystal wedge with a right-angled trapezoidal cross-section and a parallelepiped structure. The vertical side of the first beam splitter (8) is the incident end face of the incident beam of the helium-neon laser tube, and the trapezoidal wedge surface is the exit slope. The wedge angle of the first beam splitter (8) is set within the following range: in, The wedge angle of the first beam splitter (8) The refractive index is the value when the polarization direction is perpendicular to the optical axis of the first beam splitter (8). is the refractive index when the polarization direction is parallel to the optical axis of the first beam splitter (8).

3. A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output according to claim 1 or 2, characterized in that, The second beam splitter (9) and the third beam splitter (10) are both single-axis birefringent crystal wedges that are made by inverting the top and bottom surfaces of the first beam splitter (8) and enlarging or reducing them proportionally. The trapezoidal wedge surfaces of the second beam splitter (9) and the third beam splitter (10) face the trapezoidal wedge surface of the first beam splitter (8) and remain parallel. The second beam splitter (9) and the first beam splitter (8) are kept at a horizontal distance of d1; the third beam splitter (10) and the first beam splitter (8) are kept at a horizontal distance of d2. The first beam splitter (8), the second beam splitter (9), and the third beam splitter (10) are made of the same uniaxial anisotropic crystal, with their optical axes perpendicular to the direction of the incident beam propagation and parallel or perpendicular to the cross-section of the first beam splitter (8).

4. A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output according to claim 3, characterized in that, First refracted light Second refracted light The light beams propagate to the trapezoidal wedge surfaces of the second beam splitter (9) and the third beam splitter (10), respectively, where they are reflected and refracted. The resulting two reflected beams are the first reflected beam and the second reflected beam. Second reflected light The two refracted beams produced are the first output beams. Second output light The first reflected light and the first output light The frequency corresponds to the first frequency of the output light of the dual longitudinal mode helium-neon laser tube (1), and the second reflected light. Second output light The frequency corresponds to the second frequency of the output light of the dual longitudinal mode helium-neon laser tube (1).

5. A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output according to claim 4, characterized in that, The wedge angle range of the first beam splitter (8), the second beam splitter (9), and the third beam splitter (10) is set as follows: Alternatively, a polarization-insensitive micro-reflective film can be deposited on the trapezoidal wedge surfaces of the second beam splitter (9) and the third beam splitter (10). In this case, the reflected and refracted light intensities in the second beam splitter (9) and the third beam splitter (10) satisfy the following: 。 6. A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output according to claim 5, characterized in that, The first output light Second output light Based on the law of refraction and the geometric relationship between prisms, the vertical distance between the prism and the output light of the dual-longitudinal-mode helium-neon laser tube satisfies: Wherein, H1 is the first output light The distance between the output light from the dual-longitudinal-mode helium-neon laser tube and H2 is the second output light. The distance between the laser beam and the output light from the dual-longitudinal-mode helium-neon laser tube, θ1 is the distance between the laser beam and the output light from the first refracted light. The angle of refraction at the exit surface of the first beam splitter, θ2, is the second refracted light. The angle of refraction at the exit surface of the first beam splitter; in, For the first refracted light The refractive index in the first beam splitter For the second refracted light The refractive index in the first beam splitter.

7. A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output according to claim 6, characterized in that, First output light Second output light The vertical spacing H satisfies: 。 8. A thermally stabilized helium-neon laser with high extinction ratio and dual longitudinal mode output according to claim 7, characterized in that, First reflected light Second reflected light The signals are respectively input into the first photodetector (6) and the second photodetector (7) to obtain the first feedback signal I1 and the second feedback signal I2, which satisfy the following: Where k is the gain of the first photodetector (6) and the second photodetector (7); Based on the frequency stabilization control circuit module (5), the first feedback signal I1 and the second feedback signal I2 are detected, when At that time, the frequency stabilization control circuit module (5) adjusts the heating film (3) of the dual-longitudinal-mode helium-neon laser tube (1) and changes the cavity length of the resonant cavity of the dual-longitudinal-mode helium-neon laser tube (1), thereby changing the light intensity and frequency of the dual-longitudinal-mode laser until... ,at this time That is, the light intensity of the dual longitudinal mode lasers is equal, and the frequency is stable at a position symmetrical about the center of the gain curve of the helium-neon laser.

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