Adjusting device and method for the polarization direction of a laser crystal

Abstract

The application belongs to the technical field of laser, and particularly relates to a device and method for adjusting the polarization direction of a laser crystal. The device for adjusting the polarization direction of the laser crystal comprises a side-pumping module, a reference laser light source, a detection unit and an information processing unit. The side-pumping module comprises a laser crystal and a pump source surrounding the laser crystal, and the pump source is arranged to radially inject pump light to the laser crystal in a side-pumping mode. The reference laser light source is arranged at one end of the laser crystal, and the reference light emitted by the reference laser light source will be projected on the detection unit and form a light spot after passing through the laser crystal. The information processing unit can receive and display the distribution information of the light spot transmitted by the detection unit. The device for adjusting the polarization direction of the laser crystal can position and adjust the polarization direction of the laser crystal by collecting the distribution of the light spot after the reference light passes through the laser crystal under the working state of the side-pumping module, so as to solve the problems of complicated adjustment steps and large errors of the polarization direction of the laser crystal in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically relating to a device for adjusting the polarization direction of a laser crystal, and also to a method for adjusting the polarization direction of a laser crystal. Background Technology

[0002] To match subsequent laser applications such as nonlinear transformations and laser amplification, the laser light is typically required to be polarized at a specific angle, such as horizontal, vertical, or other angles. For birefringent laser crystals that directly excite linearly polarized light, the polarization axis of the crystal is usually required to be maintained at a specific angle. Due to the different purposes of laser applications, it is often necessary to adjust the polarization axis of the laser crystal.

[0003] Currently, the method for adjusting the polarization direction of a cylindrical crystal is as follows: First, a resonant cavity containing a polarizer is constructed, with the angle of the polarizer adjusted to the desired polarization direction. Then, the angle of the laser crystal is adjusted until the power output of the resonant cavity reaches its maximum value.

[0004] However, this adjustment method requires removing the side pump module and laser crystal from the resonant cavity each time, adjusting the angle, fixing the laser crystal's position, and then placing them back into the cavity. This process involves alignment and optimization of the side pump module and resonant cavity. The entire adjustment process is overly cumbersome, makes it impossible to determine the laser crystal's angle deviation, and requires optimal values ​​each time the resonant cavity is restored. This demands a high level of skill in debugging, resulting in significant adjustment errors. Summary of the Invention

[0005] The purpose of this invention is to at least solve the problems of cumbersome and error-prone steps in existing laser crystal polarization direction adjustment methods. This purpose is achieved through the following technical solution:

[0006] A first aspect of the present invention provides a device for adjusting the polarization direction of a laser crystal, the laser crystal having a birefringence effect, and the device comprising:

[0007] A side-pumping module, comprising the laser crystal and a pump source surrounding the laser crystal; the pump source radially incident pump light onto the laser crystal in a side-pumping manner;

[0008] A reference laser source is positioned close to one end of the laser crystal;

[0009] A detection unit is disposed at the other end of the laser crystal; the reference light emitted by the reference laser source passes through the laser crystal and is projected onto the detection unit to form a light spot, and the detection unit is used to measure the distribution of the light spot;

[0010] An information processing unit, which is communicatively connected to the detection unit, is used to receive and display the distribution information of the light spot.

[0011] The laser crystal polarization direction adjustment device according to the present invention locates and adjusts the polarization direction of the laser crystal by collecting the distribution of the light spot after the reference light emitted by the reference laser source passes through the laser crystal when the side pump module is working. That is, it uses the thermal focal length difference of the birefringent laser crystal to determine and adjust the polarization direction of the laser crystal, thereby quickly and effectively adjusting the polarization direction of the laser crystal to the required position, effectively solving the problem of cumbersome and error-prone steps in the existing laser crystal polarization direction adjustment process.

[0012] In addition, the laser crystal polarization direction adjustment device according to the present invention may also have the following additional technical features:

[0013] In some embodiments of the present invention, it further includes:

[0014] A shaping section is disposed on the propagation path of the reference light and is used to adjust the reference light.

[0015] In some embodiments of the present invention, the shaping part includes:

[0016] A first shaping section is disposed between the reference laser source and the laser crystal, and is used to adjust the reference light to parallel light.

[0017] In some embodiments of the present invention, the shaping part further includes:

[0018] The second shaping section is disposed between the laser crystal and the detection section, and is used to adjust the reference light to a size suitable for measurement by the detection section.

[0019] In some embodiments of the present invention, the shaping part is one or a combination of a spherical mirror, an aspherical mirror, and a diffraction grating.

[0020] In some embodiments of the present invention, it further includes:

[0021] An attenuation section is disposed between the laser crystal and the detection section, and is used to adjust the reference light to an intensity suitable for measurement by the detection section.

[0022] In some embodiments of the present invention, the laser crystal is configured as a rod-shaped structure with a circular radial cross-section.

[0023] Another aspect of the present invention provides a method for adjusting the polarization direction of a laser crystal, implemented using the aforementioned laser crystal polarization direction adjustment device, comprising the following specific steps:

[0024] The distribution of the light spot after the reference light passes through the laser crystal is obtained when the side pump module is working;

[0025] The laser crystal is adjusted according to the distribution of the light spot.

[0026] In some embodiments of the present invention, the method further includes, before the step of obtaining the spot distribution of the laser crystal under the reference light illumination when the side pump module is operating:

[0027] The distribution of the light spot after the reference light passes through the laser crystal is obtained when the side pump module is not working.

[0028] In some embodiments of the present invention, the step of adjusting the laser crystal is preceded by:

[0029] Based on the distribution of the light spots obtained from the two acquisitions, the convergence and dispersion trends of the light spots are analyzed to determine the reference axis. Attached Figure Description

[0030] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0031] Figure 1 This is a schematic diagram of the structure of the laser crystal polarization direction adjustment device according to the present invention;

[0032] Figure 2 This is a front view of the laser crystal described in this invention;

[0033] Figure 3 This is a side view of the laser crystal described in this invention;

[0034] Figure 4 This is a schematic flowchart of the method for adjusting the polarization direction of the laser crystal according to the present invention.

[0035] The markings in the attached diagram are as follows:

[0036] 1. Laser crystal; 11. Crystal facet;

[0037] 2. Reference laser source;

[0038] 3. Side pump module; 31. Pump source;

[0039] 4. Testing Department;

[0040] 5. Information Processing Department;

[0041] 6. Plastic Surgery Department; 61. First Plastic Surgery Department; 62. Second Plastic Surgery Department;

[0042] 7. Attenuation section. Detailed Implementation

[0043] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0044] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0045] Although terms such as first, second, third, etc., may be used in this document to describe multiple elements, components, regions, layers, and / or segments, these elements, components, regions, layers, and / or segments should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or segment from another. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or segment discussed below may be referred to as the second element, component, region, layer, or segment without departing from the teachings of the exemplary embodiments.

[0046] For ease of description, spatial relative terms may be used in the text to describe the relationship of one element or feature relative to another element or feature, as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "over," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure. For example, if the device in the figure is flipped, an element described as "below other elements or features" or "below other elements or features" would subsequently be oriented as "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or in other directions), and the spatial relative descriptors used in the text will be interpreted accordingly.

[0047] This invention proposes a device for adjusting the polarization direction of a laser crystal, wherein the laser crystal exhibits birefringence. The device includes a side-pumping module, a reference laser source, a detection unit, and an information processing unit. The side-pumping module includes the laser crystal and a pump source surrounding it, which radially pumps pump light onto the laser crystal from the side. The reference laser source is positioned close to one end of the laser crystal, while the detection unit is positioned at the other end. Reference light emitted from the reference laser source passes through the laser crystal and is projected onto the detection unit, forming a light spot. The detection unit measures the distribution of this light spot. Simultaneously, the information processing unit is communicatively connected to the detection unit to receive and display the light spot distribution information.

[0048] The laser crystal polarization direction adjustment device of the present invention acquires the spot distribution of the reference light emitted by the reference laser source after passing through the laser crystal when the side pump module is working. That is, it uses the thermal focal length difference of the birefringent laser crystal to locate and adjust the polarization direction of the laser crystal, so as to solve the problem that the laser crystal polarization direction adjustment steps are cumbersome and have large errors in the prior art.

[0049] Based on the above design concept, the polarization direction adjustment device for the laser crystal involved in this embodiment has an exemplary structure as follows: Figure 1As shown, in this embodiment, the laser crystal 1 is mainly selected from various birefringent laser crystals doped with Nd ions, Yb ions and other active ions, such as Nd:YVO4, Nd:YLF, Nd:KGW, Nd:LYSO, etc. After absorbing the pump light, this type of laser crystal 1 will excite polarized light, and the polarization direction of the light will be along the axial direction of the laser crystal 1. While absorbing the pump light, the laser crystal 1 will generate a thermal effect, and the thermal effect is different in different axes, specifically reflected in the different thermal performance parameters such as thermal conduction parameters, thermal expansion parameters and thermo-optical parameters. Combining these parameters, the thermal lensing effect can be simplified as (1):

[0050]

[0051] Where Pa is the total heat absorbed by the rod, L is the length of the rod, K is the thermal conductivity, A is the cross-sectional area of ​​the rod, α is the coefficient of thermal expansion, dn / dt is the refractive index as a function of temperature, and C... r C φ Here, n represents the photoelastic coefficient, and n0 represents the crystal refractive index. Therefore, the thermal focal length of laser crystal 1 along different polarization axes can be calculated.

[0052] Combination such as Figure 2 As shown, in this embodiment, the reference laser source 2 is positioned close to one end of the laser crystal 1, and the reference light emitted by the reference laser source 2 can pass through the laser crystal 1. For ease of description, the direction of the reference light's passage is referred to as the a-axis. When the pump source 31 in the side-pump module 3 is working, the pump source 31 radially incident pump light onto the laser crystal 1 in a side-pumping manner. At this time, σ-polarized light and π-polarized light are excited. In this embodiment, the laser crystal 1 is configured as a rod-shaped structure with a circular radial cross-section, and at this time, the crystal plane 11 perpendicular to the a-axis is circular. For ease of description, the direction of the σ-polarized light is referred to as the b-axis, and the direction of the π-polarized light is referred to as the c-axis, as shown below. Figure 3 As shown, both the b-axis and c-axis lie on crystal plane 11, which is perpendicular to the a-axis.

[0053] When it is necessary to adjust the direction of σ-polarized light or π-polarized light, the position of the b-axis or c-axis on the crystal plane 11 must first be determined, and the b-axis or c-axis is used as a reference axis. Then, the laser crystal 1 is adjusted so that the laser crystal 1 has the required polarization direction. In this embodiment, the adjustment of the laser crystal 1 refers to the rotational adjustment of the position of the b-axis or c-axis within the crystal plane 11 perpendicular to the a-axis.

[0054] It should be noted that the laser crystal 1 is not limited to a rod-shaped structure with a circular radial cross-section, i.e., a laser crystal with a circular crystal facet 11. Compared to other laser crystals 1 with different crystal facet 11 shapes, the adjustment reference axis and adjustment angle of a circular crystal facet 11 are more difficult to determine. Therefore, selecting a rod-shaped structure with a circular radial cross-section for the laser crystal 1 makes it easier to demonstrate the accuracy and applicability of the adjustment device.

[0055] Based on the different thermal focal length effects of laser crystal 1 along different polarization axes mentioned above, it can be seen that the spot distribution of the reference light emitted by the reference laser source 2 after irradiating laser crystal 1 is different. According to the distribution of the spot on the b-axis and c-axis, the b-axis and c-axis can be determined, thereby determining at least one reference axis for adjustment of laser crystal 1.

[0056] To reduce the impact of pump light on the laser spot distribution, in this embodiment, the pump source 31 in the side-pumping module 3 is arranged around the laser crystal 1. Furthermore, the pump source 31 radially incidents pump light onto the laser crystal 1 using a side-pumping method, ensuring that the pump light emitted by the pump source 31 is perpendicular to the reference light emitted by the reference laser source 1, thereby reducing the impact of the pump light on the final laser spot distribution. As a further feasible implementation, the pump source 31 can be a semiconductor laser diode pumping system or a lamp pumping system such as a xenon lamp or krypton lamp to provide input energy to the laser.

[0057] Still Figure 1 As shown, the reference laser source 2 can be a He-Ne laser or other reference laser source 2. In this embodiment, the reference laser source 2 is a He-Ne laser, and the laser crystal 1 is configured as an Nd:YLF crystal. First, the thermal focal length of the two polarization axes is calculated using formula (1), where the b-axis exhibits a positive lens effect and the c-axis exhibits a negative lens effect. That is, when the side pump module 3 is working, the light spot of the reference light emitted by the He-Ne laser after irradiating the laser crystal 1 will exhibit the following deformation: the direction parallel to the b-axis of the laser crystal 1 will be convergent, and the direction parallel to the c-axis of the laser crystal 1 will be divergent. At this time, the b-axis or c-axis can be determined by the distribution of the light spot. At the same time, combined with Figure 3 As shown, assuming that the polarization direction of the laser needs to be set along the direction of the dashed line c1 in the figure, the already determined c-axis needs to be set as the reference axis, and the laser crystal 1 needs to be adjusted according to the direction shown in d in the figure until the c-axis coincides with the c1 axis.

[0058] In this embodiment, the detection unit 4 uses a CCD to accurately measure the spot distribution of the reference light. It should be noted that the detection unit 4 can also be equipped with other devices to collect information on the spot distribution of the reference light after passing through the laser crystal 1. However, information collected by a CCD is more accurate, and the product is mature and readily available for purchase.

[0059] To better coordinate with the detection unit 4 and display the light spot distribution information, in this embodiment, the information processing unit 5 is configured as a computer system, which is connected to the CCD via a communication link. This computer system has at least an information receiving module, an information processing module, and a display module, enabling it to receive information output from the CCD and provide a display function for the operator to view. This configuration allows the operator to accurately and effectively obtain the light spot distribution information.

[0060] As a further preferred embodiment, the information processing module can also directly analyze the axial direction of the b-axis and c-axis, as well as the angular difference between the b-axis or c-axis and the horizontal direction. This not only helps to improve the accuracy of detection, but also provides auxiliary guidance for the adjustment of the laser crystal 1, thereby improving the efficiency of the polarization direction adjustment of the laser crystal 1.

[0061] Still Figure 1 As shown, to further refine the final detection effect of the detection unit 4, the polarization direction adjustment device of the laser crystal is further provided with a shaping unit 6. The shaping unit is located on the propagation path of the reference light and can adjust the reference light entering and exiting the laser crystal 1. In one specific embodiment, the shaping unit 6 includes a first shaping unit 61 and a second shaping unit 62. The first shaping unit 61 is located between the reference laser source 2 and the laser crystal 1, and is used to adjust the reference light emitted by the reference laser source 2 into parallel light. Shaping the reference light emitted by the reference laser source 2 into parallel light helps reduce the influence of laser beam divergence on the final detection result.

[0062] In some embodiments of the present invention, the first shaping part 61 may be one or a combination of a spherical mirror, an aspherical mirror, and a diffraction grating. Specifically, the spherical mirror, aspherical mirror, and diffraction grating may be used individually or in combination. In this embodiment, the first shaping part 61 is a two-piece beam-expanding lens group. The reference light emitted from the reference laser source 2 is expanded and shaped into parallel light after passing through the beam-expanding lens group, and the size of the light spot is comparable to the size of the laser crystal 1 rod.

[0063] In this embodiment, the second shaping unit 62 is disposed between the laser crystal 1 and the detection unit 4, and is used to adjust the reference light to a size suitable for measurement by the detection unit 4. Depending on the specific selection of the detection unit 4, the final size that can be detected varies considerably. Since the detection unit 4 used in this embodiment is a CCD, the second shaping unit 62 adjusts the final passable reference light to a spot size suitable for CCD observation. It should be noted that the second shaping unit 62 can use the same beam shaping element, so it will not be described in detail here.

[0064] Furthermore, to prevent damage to the detection unit 4 caused by the reference light, the adjustment device also includes an attenuation unit 7, which is positioned between the laser crystal 1 and the detection unit 4. This attenuation unit 7 is used to adjust the intensity of the reference light to a level suitable for measurement by the detection unit 4. In this embodiment, the function of the attenuation unit 7 is to adjust the illumination intensity of the reference light to ensure optimal detection performance of the CCD. As a preferred embodiment, the attenuation unit 7 can be any existing attenuator, and polarization-based beam splitting attenuation can be used if necessary.

[0065] Another aspect of the present invention provides a method for adjusting the polarization direction of a laser crystal, which is implemented using the aforementioned laser crystal polarization direction adjustment device. For example... Figure 4 As shown, the method includes the following specific steps:

[0066] S1: Obtain the distribution of the light spot after the reference light passes through the laser crystal 1 when the side pump module 3 is working;

[0067] S2: Adjust laser crystal 1 according to the distribution of the light spot.

[0068] Specifically, firstly, while ensuring the operation of the pump source 31 in the side pump module 3, the reference laser source 2 releases reference light. The reference light passes through the laser crystal 1 and illuminates the detection unit 4, and finally displays the light spot distribution on the information processing unit 5. Subsequently, based on the light spot distribution, the operator can adjust the laser crystal 1 to obtain the desired polarization direction.

[0069] The method for adjusting the polarization direction of a laser crystal according to the present invention utilizes the thermal focal length difference of a birefringent laser crystal 1 to locate and adjust the polarization direction of the laser crystal 1, thereby quickly and effectively adjusting the polarized light generated by the laser crystal 1 in any specified direction within the crystal plane 11.

[0070] In some embodiments of the present invention, before the step of obtaining the spot distribution of the laser crystal 1 under reference light illumination when the side pump module 3 is operating, the method further includes:

[0071] The distribution of the reference light spot after passing through the laser crystal 1 is obtained when the side pump module 3 is not working.

[0072] Specifically, the pump source 31 in the side pump module 3 is kept in a non-operational state, causing the reference laser source 2 to emit reference light, which then passes through the laser crystal 1 and illuminates the detection unit 4. At this time, the detection unit 4 detects the distribution of the laser spot itself. By detecting the distribution of the spot twice, the judgment result of the spot deformation is further improved, so as to avoid the fact that the distribution of the spot detected at the end cannot be used as a reference for adjusting the laser crystal 1 due to the properties of the laser crystal 1 itself.

[0073] In some embodiments of the present invention, the method further includes the following steps prior to adjusting the laser crystal 1:

[0074] Based on the distribution of the light spots acquired in the two acquisitions, the convergence and dispersion trends of the light spots are analyzed to determine the reference axis.

[0075] When the distribution of the detected light spot is displayed on the information processing unit 5, the operator needs to compare the two detected light spot distributions to determine the convergence and dispersion trends of the light spot, thereby accurately determining the b-axis and c-axis directions. At this time, if horizontally polarized π light needs to be output, the c-axis of the laser crystal 1 needs to be rotated to the horizontal direction, then the laser crystal 1 is fixed, and finally, the side pump module 3 and the laser crystal 1 are placed in the resonant cavity to operate, thus generating horizontally polarized π laser.

[0076] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A device for adjusting the polarization direction of a laser crystal, said laser crystal having a birefringence effect, characterized in that, The regulating device includes: A side-pumping module, comprising the laser crystal and a pump source surrounding the laser crystal; the pump source radially incident pump light onto the laser crystal in a side-pumping manner; A reference laser source is positioned close to one end of the laser crystal; A CCD detection unit is disposed at the other end of the laser crystal; the reference light emitted by the reference laser source passes through the laser crystal and is projected onto the CCD detection unit to form a light spot, and the CCD detection unit is used to accurately measure the distribution of the light spot; An information processing unit, which is communicatively connected to the CCD detection unit, is used to receive and display the distribution information of the light spot; The adjustment device is configured to acquire the distribution of the light spot after the reference light passes through the laser crystal when the side pump module is working and not working, and to compare the distribution of the light spot acquired in the two cases, analyze the convergence and dispersion trend of the light spot, determine the reference axis, and adjust the laser crystal to obtain the desired polarization direction.

2. The device for adjusting the polarization direction of a laser crystal according to claim 1, characterized in that, Also includes: A shaping section is disposed on the propagation path of the reference light and is used to adjust the reference light.

3. The device for adjusting the polarization direction of a laser crystal according to claim 2, characterized in that, The shaping unit includes: A first shaping section is disposed between the reference laser source and the laser crystal, and is used to adjust the reference light to parallel light.

4. The device for adjusting the polarization direction of a laser crystal according to claim 2, characterized in that, The shaping unit also includes: The second shaping section is disposed between the laser crystal and the CCD detection section, and is used to adjust the reference light to a size suitable for measurement by the CCD detection section.

5. The device for adjusting the polarization direction of a laser crystal according to claim 2, characterized in that, The shaping part is one or a combination of a spherical mirror, an aspherical mirror, and a diffraction grating.

6. The device for adjusting the polarization direction of a laser crystal according to claim 1, characterized in that, Also includes: An attenuation section is disposed between the laser crystal and the CCD detection section, and is used to adjust the reference light to an intensity suitable for measurement by the CCD detection section.

7. The device for adjusting the polarization direction of a laser crystal according to claim 1, characterized in that, The laser crystal is configured as a rod-shaped structure with a circular radial cross-section.

8. A method for adjusting the polarization direction of a laser crystal, implemented using the laser crystal polarization direction adjustment device according to any one of claims 1 to 7, characterized in that, The specific steps include the following: The distribution of the light spot after the reference light passes through the laser crystal is obtained when the side pump module is working; The laser crystal is adjusted according to the distribution of the light spot.

9. The method for adjusting the polarization direction of a laser crystal according to claim 8, characterized in that, Before the step of obtaining the distribution of the light spot after the reference light passes through the laser crystal when the side pump module is operating, the method further includes: The distribution of the light spot after the reference light passes through the laser crystal is obtained when the side pump module is not working.

10. The method for adjusting the polarization direction of a laser crystal according to claim 9, characterized in that, Prior to the step of adjusting the laser crystal, the following also includes: By comparing the distribution of the light spots obtained in the two acquisitions, the convergence and dispersion trends of the light spots are analyzed to determine the reference axis.

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