CN114384068B - Measuring device, measuring method and application for measuring weak anisotropy in large-size isotropic laser medium - Google Patents

Measuring device, measuring method and application for measuring weak anisotropy in large-size isotropic laser medium Download PDF

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CN114384068B
CN114384068B CN202111619346.6A CN202111619346A CN114384068B CN 114384068 B CN114384068 B CN 114384068B CN 202111619346 A CN202111619346 A CN 202111619346A CN 114384068 B CN114384068 B CN 114384068B
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laser
cavity
light
laser medium
polarization
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CN114384068A (en
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李丙轩
张戈
黄凌雄
廖文斌
林长浪
陈玮冬
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Fujian Institute of Research on the Structure of Matter of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/02—Testing optical properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/02—Testing optical properties
    • G01M11/0207—Details of measuring devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N2021/0106—General arrangement of respective parts
    • G01N2021/0112—Apparatus in one mechanical, optical or electronic block
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N2021/8477—Investigating crystals, e.g. liquid crystals

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Abstract

The invention discloses a weak anisotropy measuring device and a weak anisotropy measuring method for measuring a large-size isotropic laser medium, and belongs to the technical field of material performance testing. The measuring device of the present invention includes: the device comprises a light condensing cavity, a pumping source, a laser medium, a laser resonant cavity, a polarization testing module, a signal analysis module, a weak anisotropy calculating module and an indication light path module; the pump source and the laser medium are arranged in the light-gathering cavity, wherein the laser medium is positioned at the focus of the light-gathering cavity; the light condensation cavity is arranged in the resonant cavity. The invention also provides a measuring method by the measuring device and application thereof. The method solves the problem that the weak anisotropy of the isotropic laser medium is difficult to accurately measure in the prior art, and greatly improves the detection precision, speed and accuracy by adopting a mode of combining polarization detection and signal analysis.

Description

Measuring device, measuring method and application for measuring weak anisotropy in large-size isotropic laser medium
Technical Field
The invention relates to a measuring device, a measuring method and application for measuring weak anisotropy in a large-size isotropic laser medium, and belongs to the technical field of material performance testing.
Background
Shang Kaifei et al report an isotropic solid state laser Nd: the polarization locking of the eigenmodes in the YAG laser shows a polarization coupling mechanism based on coherent combination of the eigenmodes of the isotropic solid-state laser for the first time, and in the FP cavity Nd-YAG laser, the direct linear polarization output of the isotropic solid-state laser is realized by a simple and easy-to-operate method through a fine tuning cavity mirror mode. On this basis, the essential distinction of the linear polarization from the normal polarization eigenstate is found, including the extremely sensitive character of its polarization and the singular character of the polarization resolving spot. The reason that isotropic solid state lasers can directly output linear polarization is pointed out as Nd: the YAG crystal has weak phase anisotropy due to self defects or thermal effect, namely, the phase anisotropy caused by the crystal is compensated by the loss anisotropy of the cavity in a mode of fine tuning the cavity mirror, so that the frequency degeneracy of the polarization eigenmodes in the cavity is realized, the coherence condition is met between the two orthogonal polarization eigenmodes, and the coherence superposition can be carried out to realize linear polarization output. However, it is not proposed how to measure Nd: weak anisotropy of isotropic laser medium such as YAG crystal.
Wang Xiaobo et al published in the field of mechanical science, research on grinding residual stress of crystalline materials based on a single-particle action model, wide application of nanoindentation technology in the field of material performance test, quantitative analysis on residual stress on the surface of a workpiece based on nanoindentation test of the surface of the material and by means of computer finite element numerical simulation. But this scheme is less accurate.
CN110161562B relates to a method and a system for inverting the weakness of a crack in an inclined transverse isotropic medium, wherein a method and a system for inverting the weakness of a crack in an inclined transverse isotropic medium are disclosed, the method uses stiffness matrixes of a vertical transverse isotropic medium and a Bond matrix, derives the stiffness matrix of the inclined transverse isotropic medium according to the weakness of the crack and the inclination angle, combines stiffness disturbance and scattering theory, separates a weak contrast interface of the two weak anisotropic inclined transverse isotropic mediums, obtains the azimuth angle of the reflection coefficient of a PP wave under the interface, uses the inclination angle as priori information, utilizes partial incidence angle superposition azimuth seismic data to realize azimuth pre-stack inversion, and estimates the weakness of the crack in a bayesian frame according to inversion results. The disadvantage is that the scheme is only suitable for isotropic media with relatively large propagation of seismic waves, and is not suitable for laser media with relatively small size, such as crystals, ceramics, gases, and the like. The laser working substances are commonly divided into solid, liquid, gas and semiconductor according to gain media. The most commonly used laser media are crystals, transparent ceramics, glass and the like, and the gain media have weak anisotropism inside the media due to processing, self-growth defects or external pressure and temperature and the like, especially for isotropic laser media such as YAG crystals, GGG crystals, transparent laser ceramics, glass and the like, the weak anisotropism can lead to the damage of the integrity of the laser media, and under the condition of high-power operation, the laser media are easy to generate unnecessary deformation and even damage, so that the development of laser is severely restricted. Therefore, it is very important to conduct a weak anisotropy test with respect to an isotropic laser medium in order to accurately evaluate the quality of the isotropic laser medium and reliability, lifetime, etc. during use.
The weak anisotropy of the current test materials is usually obtained by measuring the variables related to the weak anisotropy, such as elastic strain, refractive index, displacement and the like, around the test materials and then deducing the variables. The current measurement methods mainly include photoelastic method, X-ray diffraction method, neutron diffraction method, micro raman spectroscopy, and the like. Photoelastic methods and X-ray diffraction methods are widely used for stress detection of single crystal materials, but these methods have low accuracy (about 10 -5 ) The X-ray and neutron diffraction methods have high cost, and can not accurately test the weak anisotropy of the isotropic laser medium. Therefore, there is a need to develop test devices and methods for weak anisotropy in isotropic laser media.
Disclosure of Invention
The invention overcomes the defects in the prior art and provides a measuring device, a measuring method and application for measuring weak anisotropy in a large-size isotropic laser medium.
The present invention provides a measuring device comprising: the device comprises a light condensing cavity, a pumping source, a laser medium, a laser resonant cavity, a polarization testing module, a signal analysis module, a weak anisotropy calculating module and an indication light path module; the pump source and the laser medium are arranged in the light-gathering cavity, wherein the laser medium is positioned at the focus of the light-gathering cavity; the light condensation cavity is arranged in the resonant cavity;
the light-gathering cavity is used for focusing and irradiating the pump light on a laser medium, and the reflectivity of the inner wall of the light-gathering cavity to the pump light is more than 90%;
the power of the pumping source is not more than 100W, and the pumping source emits pumping light for pumping or exciting a laser medium;
the laser medium is selected from isotropic laser medium, and the size of the laser medium is phi (1-10) mm (10-100) mm. Under the irradiation of the pumping light, ions of the laser medium are pumped from a low energy level to a high energy level to form population inversion, and laser is generated through feedback amplification of a resonant cavity;
the laser resonant cavity is used for providing positive feedback in the laser generating process and guaranteeing continuous oscillation of laser;
the polarization testing module is used for testing the polarization state of the output laser and judging whether the laser resonant cavity is in an optimal measurement state or not;
the signal analysis module is used for testing transient power fluctuation and spectrum information of the output laser;
the weak anisotropy calculation module calculates weak anisotropism of the laser medium at the position to be measured according to the results of the polarization test module and the signal analysis module;
the indication light path module provides an indication light path for marking a position to be measured and/or for adjusting a cavity mirror angle of the laser resonant cavity.
According to an embodiment of the invention, the inner wall of the light gathering cavity is plated with a specular or diffuse reflecting material.
Preferably, the specular reflective material is selected from metals commonly used in the art, which can achieve high reflectivity for pump light, such as gold or silver, with a reflectivity of greater than 95%.
Preferably, the diffuse reflection material is selected from diffuse reflection materials commonly used in the technical field, and has high diffuse reflectance to pump light, such as ceramics and silica gel, and the diffuse reflectance is more than 90%.
According to an embodiment of the invention, the wavelength of the pump source corresponds to the absorption wavelength of the laser medium.
Preferably, the pump source is selected from a laser or a flash lamp. Preferably, the power of the pump source is greater than 30W and less than 100W, for example 50-100W. The laser in the invention is selected from lasers commonly used in the technical field, so long as pump light can be provided to enable the laser medium to realize particle number inversion, for example, the pump source is a semiconductor laser with highest power of 100W. Illustratively, the pump source is a semiconductor laser with 808nm and highest power of 100W. Illustratively, the pump source is a 946nm semiconductor laser with highest power of 100W. Illustratively, the pump source is a 976nm semiconductor laser with a highest power of 100W. Illustratively, the flash lamp is a xenon lamp or a krypton lamp.
According to an embodiment of the present invention, the laser medium is selected from at least one of laser crystals, laser ceramics, laser glass, gases, vapors, organic dyes, etc.
Illustratively, the laser medium is selected from Nd manufactured by foci: YAG crystals with a size phi 5mm x 100mm. Illustratively, the laser medium is selected from Er glass manufactured by Fu Jing, inc., having a size of phi 3mm 50mm. Illustratively, the laser medium is selected from Yb produced by foci: YAG laser transparent ceramic with the size phi of 3mm is 50mm. Illustratively, the laser medium is selected from the group consisting of c-cut Nd: YVO manufactured by Fujingsu corporation 4 Laser crystal with the size phi 3mm is 30mm.
According to an embodiment of the invention, the pump source and the laser medium are preferably fixed in a light collecting cavity, the light collecting cavity is fixed in a four-dimensional adjusting frame, and different positions to be measured are switched through movement of the four-dimensional adjusting frame. Preferably, the position to be measured refers to a position where the pumping light irradiates on the laser medium. Preferably, the four-dimensional adjusting frame can be adjusted in four dimensions, and specifically comprises at least one of horizontal movement, vertical movement, horizontal rotation and up-and-down rotation.
According to the embodiment of the invention, the laser resonant cavity can change different cavity types according to different laser media, for example, change different cavity types according to the thermal effect doping concentration of the laser media and the like. Preferably, the cavity type of the laser resonant cavity includes, but is not limited to, at least one of a flat cavity, a flat concave cavity, a concave flat cavity, a double concave cavity, a convex flat cavity, a flat convex cavity, a double convex cavity, and the like.
According to an embodiment of the invention, the polarization testing module comprises a polarization polarizing prism, for example a graticule prism. Preferably, the graticule prism is located on an optical path of the output laser light and is rotatable about an axis of the optical path. Further preferably, the graticule prism is fixed to a mount that rotates centering on the optical path. Further preferably, the fixed frame is marked with an angle value, so that the rotation angle value can be accurately read.
Preferably, the polarization testing module further comprises a power meter, wherein the power meter is used for recording the power of the polarized output laser.
According to an embodiment of the present invention, the signal analysis module sequentially includes a photodetector, an oscilloscope, and a signal analyzer, where the signal analyzer is configured to measure a frequency difference signal of the polarized laser beam, and the frequency difference signal is preferably Δν. Preferably, when the output laser light is incident on the photodetector, the photodetector generates a signal that is transmitted to an oscilloscope and a signal analyzer.
According to the embodiment of the invention, the weak anisotropy calculation module obtains weak anisotropism of the laser medium at the position to be measured according to a first formula and a second formula.
Preferably, the first formula is: per=10×lg (P0/P1) (dB), where PER represents the polarization ratio of the output laser light, P1 represents the minimum power of the polarized output laser light, P0 represents the maximum power of the polarized output laser light, and P0 and P1 are in mW.
Preferably, the second formula is: a=pi×Δν/Δν 0 Wherein Deltav 0 The value of c/2L, a represents the weak anisotropy of the isotropic laser medium, pi is the circumference ratio, Δv is the frequency difference generated by the anisotropy of the laser medium, L is the equivalent cavity length of the laser resonant cavity, and c is the speed of light.
According to an embodiment of the invention, the measuring device is further provided with an external field applying unit for applying an external field to the laser medium. Preferably, the external field includes, but is not limited to, at least one of pressure, temperature, electric field, and the like.
The invention also provides a measuring method, which is carried out by adopting the measuring device, and comprises the following steps:
(1) And outputting pumping light through a pumping source, calibrating the position of the indicating light irradiated on the laser medium as a position to be measured, and adjusting the cavity mirror of the laser resonant cavity so that the normal line of the cavity mirror coincides with the indicating light path.
Preferably, the power of the pump light is adjusted to maximize the power of the output laser light. It is further preferred that the angle of the cavity mirror of the laser resonator is fine tuned to maximize the power of the output laser light. In the invention, the angle of the resonant cavity and the angle of the cavity mirror of the resonant cavity refer to the angles of the normal line of the cavity mirror and the indication light path.
Preferably, the position to be measured can be switched by a four-dimensional adjusting frame.
(2) And recording power values of the output laser under different polarization angles by rotating the Greenwich prism in the polarization test module, and calculating the polarization ratio of the output laser according to the first formula.
Preferably, the graticule prism is rotated by rotating the fixing frame, and the angle value on the fixing frame is recorded at the same time, namely the polarization angle. Preferably, the polarization angle is 0 ° -360 °.
(3) And (3) fine tuning the angle of the cavity mirror of the laser resonant cavity, and repeating the steps (1) - (2) to enable the polarization ratio to reach the minimum value.
Preferably, the angle of the laser resonant cavity is-10 degrees to 10 degrees, and the angle of the laser resonant cavity refers to the angle between the normal line of the cavity mirror and the indication light path.
(4) When the polarization ratio reaches the lowest value, the cavity mirror angle of the laser resonant cavity is kept unchanged, the output laser is connected into the signal analysis module, and frequency difference signals Deltav and Deltav are measured 0 Wherein Deltav is the frequency difference generated by the anisotropy of the laser medium, deltav 0 The longitudinal mode interval is kept consistent with the value of c/2L, L is the equivalent cavity length of the laser resonant cavity, and c is the light speed;
(5) And calculating weak anisotropy of the laser medium at the position to be measured according to the second formula.
The invention also provides an application of the measuring device or the measuring method for measuring the weak anisotropy of the isotropic laser medium in the field of material performance testing, preferably in the field of lasers.
The invention also provides a laser which comprises the measuring device or adopts the measuring method to measure the weak anisotropy of the laser medium.
The beneficial effects are that:
the measuring device of the invention is suitable for measuring large-size laser media (for example, the size range is phi (1-10) mm (10-100) mm), wherein the pump source is arranged on the non-end face (such as the side face) of the testing device, and the pump source is usually selected as the pump source with the power of not more than 100W.
The invention overcomes the defect of lower precision (10) -5 ) The measuring device and the measuring method can reach 10-degree -12 High precision testing of pi is important in accurately assessing the quality of isotropic laser media, reliability during use, lifetime, etc.
The invention adopts a mode of combining polarization detection and signal analysis, thereby greatly improving the detection precision, speed and accuracy.
The measuring device and the measuring method are efficient and quick, the measuring time is short, and the measuring result can be obtained in about 30 minutes.
Drawings
Fig. 1 is a schematic view of a measuring device of the present invention, wherein:
1-a pump source; 2-a light gathering cavity; 3-a laser resonator; 4-laser medium; a 5-polarization test module; 6-a signal analysis module; 7-a weak anisotropy calculation module; 8-indicates the optical path.
Fig. 2 is Nd in example 1: examples of measurement results of weak anisotropy of YAG crystal.
Detailed Description
The technical scheme of the invention will be further described in detail below with reference to specific embodiments. It is to be understood that the following examples are illustrative only and are not to be construed as limiting the scope of the invention. All techniques implemented based on the above description of the invention are intended to be included within the scope of the invention.
Unless otherwise indicated, the starting materials and reagents used in the following examples were either commercially available or may be prepared by known methods.
The present invention provides a measuring device for measuring weak anisotropy in an isotropic laser medium, as shown in fig. 1, comprising: the system comprises a pumping source 1, a light condensing cavity 2, a laser resonant cavity 3, a laser medium 4, a polarization testing module 5, a signal analyzing module 6, a weak anisotropy calculating module 7 and an indication light path 8; wherein, the liquid crystal display device comprises a liquid crystal display device,
the pump source 1 is used for providing pump light or excitation for a laser medium to obtain output laser; preferably, the wavelength of the pumping source corresponds to the absorption wavelength of the laser medium, ions in the laser medium can be pumped from a low energy level to a high energy level to form particle number inversion, and laser is generated through feedback amplification of the resonant cavity;
the light-gathering cavity 2 is used for focusing and irradiating pumping light of a pumping source on a laser medium, and the reflectivity of the inner wall of the light-gathering cavity to the pumping light is higher than 90%; the laser medium 4 is positioned at the focus of the light condensing cavity 2;
the laser medium 4 is selected from isotropic laser medium, and is used for realizing the population inversion under the irradiation of pump light; the laser medium 4 and the pump source 2 are arranged in the light-gathering cavity, and are preferably fixed in the light-gathering cavity;
the laser resonant cavity 3 is used for providing positive feedback in the laser generating process and guaranteeing continuous oscillation of output laser;
the polarization testing module 5 is used for testing the polarization state of the laser and judging whether the laser resonant cavity 3 is in an optimal testing state or not;
the signal analysis module 6 is used for testing transient power fluctuation and spectrum information of the output laser; calibrating the position of the pumping light irradiated on the laser medium as a position to be measured;
the weak anisotropy calculation module 7 is used for calculating weak anisotropy of the laser medium at the position to be measured according to the results of the polarization test module and the signal analysis module;
the indication light path module 8 provides an indication light path for marking a position to be measured and/or for adjusting an angle of a cavity mirror of the laser resonator.
In one embodiment, the inner wall of the light gathering cavity is plated with a specular reflection material or a diffuse reflection material. Preferably, the specular reflective material is selected from metals commonly used in the art, which can achieve high reflectivity for pump light, such as gold or silver, with a reflectivity of greater than 95%. Preferably, the diffuse reflection material is selected from diffuse reflection materials commonly used in the technical field, and has high diffuse reflectance to pump light, such as ceramics and silica gel, and the diffuse reflectance is more than 90%.
In one embodiment, the pump source 1 is selected from a laser or a flash lamp. Preferably, the power of the pump source is not more than 100W, preferably more than 30W and 100W, for example 50-100W. The laser is selected from lasers commonly used in the technical field, so long as pump light can be provided to enable the laser medium to realize particle number inversion, for example, the pump source is a semiconductor laser with highest power of 100W. For example, the pump source 1 is a semiconductor laser with 808nm and highest power of 100W. Illustratively, the pump source is a 946nm semiconductor laser with highest power of 100W. Illustratively, the pump source is a 976nm semiconductor laser with a highest power of 100W. Illustratively, the flash lamp is a xenon lamp or a krypton lamp.
In one embodiment, the inner wall of the condensing cavity 2 reflects the pump light and focuses the pump light on the laser medium 4.
In one embodiment, the laser resonator 3 may change different cavity types according to different laser media 4, for example, change different cavity types according to a thermal effect doping concentration of the laser media 4, etc. Preferably, the cavity type of the laser resonator 3 includes, but is not limited to, at least one of a flat cavity, a flat concave cavity, a concave flat cavity, a double concave cavity, a convex flat cavity, a flat convex cavity, a double convex cavity, and the like.
In one embodiment, the lasing medium 4 includes, but is not limited to, a laser crystal, a laser ceramic, a laserAt least one of glass, gas, steam, organic dye, and the like. Preferably, the laser medium 4 is at least one selected from a laser crystal, a laser ceramic, a laser glass, and the like, and is used for realizing the population inversion under the irradiation of the pump light. Preferably, the laser medium has a size of phi (1-10) mm x (10-100) mm. Illustratively, the laser medium is selected from Nd: YAG crystals with a size of phi 5 x 100mm. Illustratively, the laser medium is selected from Yb produced by foci: YAG laser transparent ceramic with the size phi of 3mm is 50mm. Illustratively, the laser medium is selected from the group consisting of c-cut Nd: YVO manufactured by Fujingsu corporation 4 Laser crystal with the size phi 3mm is 30mm.
In a specific scheme, the pump source 1 and the laser medium 4 are fixed in the light condensing cavity 2, the whole light condensing cavity is fixed in the four-dimensional adjusting frame, and different positions to be detected are switched through movement of the four-dimensional adjusting frame. Preferably, the position to be measured refers to a position where the pump light is irradiated on the laser medium 4. Preferably, the four-dimensional adjusting frame can move in four dimensions, and specifically comprises at least one of horizontal movement, vertical movement, horizontal rotation and up-and-down rotation.
In one embodiment, the polarization testing module 5 includes a polarization polarizing prism and a power meter, such as a glaring prism, and the polarization state of the output laser light is the polarization ratio of the output laser light. Preferably, the graticule prism is located on an optical path of the output laser light and is rotatable about an axis of the optical path. Further preferably, the graticule prism is fixed to a mount that rotates about an optical path of the output laser. Further preferably, the fixing frame is marked with an angle value, and the rotation angle value can be accurately read. Preferably, the polarization ratio of the output laser light is calculated according to the first formula by rotating the graticule prism and recording the power values at different angles.
Preferably, the first formula is: per=10×lg (P0/P1) (dB), where PER represents the polarization ratio of the output laser light, P1 represents the minimum power of the polarized output laser light, and P0 represents the maximum power of the polarized output laser light in mW.
Preferably, the power meter is used for recording the power of the laser after passing through the glaring prism.
In a specific embodiment, the signal analysis module includes a photodetector, an oscilloscope, and a signal analyzer, where the signal analyzer is configured to measure a frequency difference signal of the polarized laser beam, and the frequency difference signal is preferably Δν, Δν 0 Δν is a frequency difference generated by anisotropy of laser medium, wherein Δν is a frequency difference generated by anisotropy of laser medium 0 For longitudinal mode spacing, the c/2L value should be consistent. Preferably, when the output laser light is incident on the photodetector, the photodetector generates a signal that is transmitted to an oscilloscope and a signal analyzer.
In a specific scheme, the weak anisotropy calculating module is used for calculating weak anisotropy of the laser medium at the position to be measured according to a second formula according to results of the polarization testing module and the signal analyzing module.
Preferably, the second formula is a=pi×Δν/Δν 0 Wherein A represents weak anisotropy of an isotropic laser medium, pi is a circumference ratio, and Deltav 0 Δν is the frequency difference measured by the signal analyzer, L is the equivalent cavity length of the laser resonant cavity, and c is the light speed.
In a specific embodiment, the measuring device is further provided with an external field applying unit for applying an external field to the laser medium. Preferably, the external field includes, but is not limited to, at least one of pressure, temperature, electric field, and the like.
Example 1
The weak anisotropy of the isotropic laser medium 4 is measured by adopting the measuring device, wherein the pumping source 1 is a semiconductor laser with 808nm and highest power of 100W; the laser medium 4 is selected from Nd manufactured by foci: YAG crystal with the size phi 5mm is 100mm, and the front surface and the rear surface of the crystal are respectively provided with plated films AR@806 nm and AR@1064nm which are high in transmission of pumping light and output laser in a film plating mode.
The device of this embodiment actually measures the above Nd: the measurement method of weak anisotropy of YAG crystals specifically comprises the following steps:
(1) Aligning the light condensing cavity 2, the laser resonant cavity 3 and the reference indication light path 8, increasing the power of pump light, and finely adjusting the angle of a cavity mirror of the laser resonant cavity 3, wherein the angle of the laser resonant cavity refers to the angle between the normal direction of the cavity mirror and the indication light path, and the angle of the cavity mirror of the laser resonant cavity is-10 degrees to 10 degrees, so that the output laser power is maximum;
(2) Fixing the angle of a cavity mirror of the laser resonant cavity 3, and measuring the polarization ratio of the output laser by using the polarization testing module 5, wherein the method specifically comprises the following steps: rotating the graticule prism, recording power values under different angles, wherein the power values are 105mW when the rotation angle is 0 DEG, 107mW when the rotation angle is 30 DEG, 109mW when the rotation angle is 60 DEG and 110mW when the rotation angle is 90 DEG; according to the first formula, calculating to obtain the polarization ratio of the output laser to be 0.202dB;
(3) Fine tuning the angle of the laser resonator 3 (about 0.02 °), and repeating steps (1) - (2) until the calculated polarization ratio reaches a minimum value, which in this embodiment is 0.202dB.
(4) When the polarization ratio reaches the lowest value, the angle of the laser resonant cavity 3 is kept unchanged, the output laser is connected to the signal analysis module 6, and the measured frequency difference signal is Deltav=1 MHz, deltav 0 =1000 MHz, where Δν 0 The longitudinal mode interval is consistent with the value of c/2L, wherein L is the equivalent cavity length of the laser resonant cavity 3, and c is the speed of light.
(5) The weak anisotropy calculating module 7 calculates weak anisotropy of the laser medium at the position to be measured according to a second formula, wherein the second formula is a=pi×Δν/Δν 0 Wherein A represents weak anisotropy of the isotropic laser medium, pi is a circumference ratio, and Deltav is the frequency difference signal Deltav measured in the step (2).
The test results of this example are shown in fig. 2, and the weak anisotropy a=0.001 pi is calculated by the second formula.
Example 2
In the embodiment, the measuring device is adopted to measure the weak anisotropy of the isotropic laser medium 4, wherein the pumping source 1 is a semiconductor laser with 976nm and highest power of 100W; the laser medium 4 is selected from Er glass produced by Fu crystal company, the size is phi 3mm 50mm, and the front and back surfaces of the crystal are respectively provided with coating films AR@976nm and AR@1535nm which are high in transmission of pump light and output laser in a coating mode.
The device of this example actually measures the weak anisotropy of the above Er glass, the measurement method is the same as that of example 2, wherein: the minimum power P1 of the polarized output laser is 350mW, and when the maximum power P0 of the polarized output laser is 355mW, the corresponding minimum polarization ratio is 0.0616dB.
Under the condition of minimum polarization ratio, the angle of the laser resonant cavity 3 is kept unchanged, the output laser of the laser medium 4 is connected to the signal analysis module 6, and the measured frequency difference signal is Deltav=50Hz, deltav 0 The test result of this example is shown in fig. 2, and the weak anisotropy a=0.00000005 pi is calculated by the second formula.
Example 3
The weak anisotropy of the isotropic laser medium 4 is measured by adopting the measuring device, wherein the pumping source 1 is a semiconductor laser with 946nm and highest power of 100W; the laser medium 4 is selected from Yb produced by Fujingsu corporation: YAG laser transparent ceramic with the size phi of 3mm and 50mm is provided with coating films AR@946nm and AR@1030nm which are high in transmission of pumping light and output laser respectively on the front surface and the rear surface of the crystal in a coating mode.
The device of the embodiment actually measures the Yb: the weak anisotropy of YAG laser transparent ceramics is measured by the same method as in the embodiment 2, wherein the minimum power P1 of polarized output laser is 195mW, the maximum power P0 of polarized output laser is 210mW, and the corresponding minimum polarization ratio is 0.322dB;
under the condition of minimum polarization ratio, the angle of the laser resonant cavity 3 is kept unchanged, the output laser of the laser medium 4 is connected into the signal analysis module 6, and the measured frequency difference signal is Deltav=30 kHz, deltav 0 The weak anisotropy a=0.00003 pi is calculated by the second equation.
Example 4
The embodiment adopts the measuring device to measure the weak anisotropy of the isotropic laser medium 4, wherein the pumping source 1 adopts semiconductor laser with 808nm and highest power of 100WA device; the laser medium 4 is selected from c-cut Nd: YVO manufactured by Fujingsu corporation 4 The size of the laser crystal is phi 3mm which is 30mm, and the front surface and the rear surface of the crystal are respectively provided with a coating AR@806 nm and AR@1064nm which are high in transmission of pumping light and output laser in a coating mode.
The device of the embodiment actually measures the Nd: YVO of the c-cut 4 The weak anisotropy of the laser crystal was measured in the same manner as in example 2, wherein the minimum power P1 of the polarized output laser was 50mW, the maximum power P0 of the polarized output laser was 52mW, and the corresponding minimum polarization ratio was 0.17dB;
under the condition of minimum polarization ratio, the angle of the laser resonant cavity 3 is kept unchanged, the output laser of the laser medium 4 is connected into the signal analysis module 6, and the measured frequency difference signal is Deltav=160 Hz, deltav 0 The weak anisotropy a= 0.00000016 pi is calculated by the second equation above, which is=1000 MHz.
It is clear from examples 1 to 4 that different isotropic laser media can obtain high-precision test results, so that weak anisotropy of the isotropic laser media can be measured with high measurement precision by the measuring device and the measuring method of the present invention.
The above description has been given of exemplary embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, or the like, which are within the spirit and principles of the present invention, should be made by those skilled in the art, and are intended to be included within the scope of the present invention.

Claims (17)

1. A measurement device, the measurement device comprising: the device comprises a light condensing cavity, a pumping source, a laser medium, a laser resonant cavity, a polarization testing module, a signal analysis module, a weak anisotropy calculating module and an indication light path module; the pump source and the laser medium are arranged in the light-gathering cavity, wherein the laser medium is positioned at the focus of the light-gathering cavity; the light condensation cavity is arranged in the resonant cavity;
the power of the pumping source is not more than 100W, and the pumping source emits pumping light for pumping or exciting a laser medium;
the light-gathering cavity is used for focusing and irradiating the pump light on a laser medium, and the high reflectivity of the inner wall of the light-gathering cavity to the pump light is more than 90%;
the size of the laser medium is phi (1-10) mm (10-100) mm, the laser medium is selected from isotropic laser medium, ions of the laser medium are pumped from low energy level to high energy level to form particle number inversion under the irradiation of the pumping light, and laser is generated through feedback amplification of a resonant cavity;
the laser resonant cavity is used for providing positive feedback in the laser generating process and guaranteeing continuous oscillation of laser;
the polarization testing module is used for testing the polarization state of the output laser and judging whether the laser resonant cavity is in an optimal measurement state or not;
the signal analysis module is used for testing transient power fluctuation and spectrum information of the output laser;
the weak anisotropy calculation module calculates weak anisotropism of the laser medium at the position to be measured according to the results of the polarization test module and the signal analysis module;
the indication light path module provides an indication light path for marking a position to be measured and/or for adjusting a cavity mirror angle of the laser resonant cavity.
2. The measurement device of claim 1, wherein an inner wall of the light collection cavity is plated with a specular or diffuse reflective material;
and/or the wavelength of the pump source corresponds to the absorption wavelength of the laser medium;
and/or the pump source is selected from a laser or a flash lamp;
and/or the power of the pump source is greater than 30W and 100W.
3. A measuring device according to claim 1 or 2, characterized in that the pump source is a semiconductor laser with a highest power of 100W.
4. The measurement device of claim 1, wherein the laser medium is selected from at least one of a laser crystal, a laser ceramic, a laser glass, a gas, a vapor, an organic dye;
and/or the pump source and the laser medium are fixed in a light condensing cavity, the light condensing cavity is fixed in a four-dimensional adjusting frame, and different positions to be detected are switched through the movement of the four-dimensional adjusting frame;
and/or the position to be measured refers to the position where the pumping light irradiates on the laser medium, and the position to be measured should be consistent with the position where the indicating light irradiates on the laser medium.
5. The measurement device of claim 4, wherein the four-dimensional adjustment frame is adjustable in four dimensions, including at least one of horizontal movement, vertical movement, horizontal rotation, up and down rotation.
6. The measurement device of claim 1, wherein the laser resonator varies different cavity types according to different laser media;
and/or the polarization testing module comprises a polarization polarizing prism; and/or the polarization testing module further comprises a power meter, wherein the power meter is used for recording the power of the polarized output laser.
7. The measurement device of claim 6, wherein the cavity of the laser resonator comprises at least one of a flat cavity, a flat concave cavity, a concave flat cavity, a double concave cavity, a convex flat cavity, a flat convex cavity, and a double convex cavity;
the polarization polarizing prism is positioned on the optical path of the output laser and rotates around the axis of the optical path.
8. The measurement device of claim 7, wherein the polarizing prism is fixed to a mount that rotates about an optical path.
9. The measurement device of claim 1, wherein the signal analysis module comprises a photodetector, an oscilloscope, and a signal analyzer in order, wherein the signal analyzer is configured to measure a frequency difference signal of the polarized laser beam, and the frequency difference signal is Δν.
10. The measurement device of claim 9, wherein the photodetector generates a signal that is transmitted to an oscilloscope and a signal analyzer when the output laser light is incident on the photodetector.
11. The measurement device of claim 1, wherein the weak anisotropy calculation module obtains weak anisotropies of the laser medium at the position to be measured according to a first formula and a second formula;
the first formula is: per=10×lg (P0/P1) dB, where PER represents the polarization ratio of the output laser light, P1 represents the minimum power of the polarized output laser light, P0 represents the maximum power of the polarized output laser light, and the units of P0 and P1 are mW;
the second formula is: a=pi×Δν/Δν 0 Wherein Deltav 0 The value of c/2L, a represents the weak anisotropy of the isotropic laser medium, pi is the circumference ratio, Δv is the frequency difference generated by the anisotropy of the laser medium, L is the equivalent cavity length of the laser resonant cavity, and c is the speed of light.
12. The measurement device according to claim 1, characterized in that the measurement device is further provided with an external field application unit for applying an external field to the laser medium.
13. The measurement device of claim 12, wherein the external field comprises at least one of pressure, temperature, and electric field.
14. A measurement method performed using the measurement device according to any one of claims 1 to 13, the measurement method comprising the steps of:
(1) The method comprises the steps that pump light is output through a pump source, the position, irradiated by the pump light, of a laser medium is calibrated to be a position to be measured, and the position to be measured is consistent with the position, irradiated by the indicating light, of the laser medium;
(2) Recording power values of output laser under different polarization angles by rotating a polarization polarizing prism in the polarization testing module, and calculating the polarization ratio of the output laser according to a first formula;
(3) Fine tuning the angle of the laser resonant cavity, and repeating the steps (1) - (2) to enable the polarization ratio to reach the lowest value;
(4) When the polarization ratio reaches the highest value, the angle and the polarization angle of the laser resonant cavity are kept unchanged, the output laser is connected into the signal analysis module, and frequency difference signals Deltav and Deltav are measured 0 Wherein Deltav is the frequency difference generated by the anisotropy of the laser medium, deltav 0 C/2l, l is the equivalent cavity length of the laser resonator, c is the speed of light;
(5) Calculating weak anisotropy of the laser medium at the position to be measured according to a second formula;
wherein the first and second formulas have the meaning as set forth in claim 11.
15. The method according to claim 14, wherein in the step (1), an angle of the laser resonator, which is an angle between a normal direction of the cavity mirror and the indication light path, is finely adjusted so as to maximize power of the output laser;
and/or the position to be detected is switched through a four-dimensional adjusting frame;
and/or rotating the gram prism through rotating the fixing frame, and recording the angle value on the fixing frame at the same time, namely, the polarization angle;
and/or the angle of the laser resonant cavity is-10 degrees to 10 degrees;
and/or the polarization angle is 0 ° -360 °.
16. Use of a measuring device according to any one of claims 1 to 13 or a measuring method according to claim 14 or 15 for measuring the weak anisotropy of an isotropic laser medium in the field of material property testing.
17. A laser comprising a measuring device according to any one of claims 1-13 or a measuring method according to claim 14 or 15 for measuring weak anisotropy of the laser medium.
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AU6033386A (en) * 1985-09-23 1987-03-26 Northern Telecom Limited Test instrument
DE4105192A1 (en) * 1990-02-26 1991-08-29 Stefan Oelckers Polarimetric testing of surface properties and transparent material - by evaluating difference between reflected s and p polarised components
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