CN113310905B - Device and method for measuring thermal stress in high-power laser cavity - Google Patents
Device and method for measuring thermal stress in high-power laser cavity Download PDFInfo
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Abstract
The invention provides a device and a method for measuring thermal stress in a high-power laser cavity, which are used for measuring thermal stress distribution of a gain medium target area of a laser gain module. The gain laser detection compensation system comprises a laser high-reflection mirror, a laser output mirror, a laser polaroid and a power meter. The detection light detection compensation system comprises a detection light source, a detection light polarizer, a first detection light 1/4 wave plate, a spectroscope, a second detection light 1/4 wave plate, a detection light analyzer and a CCD array. The method can measure the thermal stress distribution in the crystal in a gain state in real time, optimize the pumping power distribution to realize thermal stress distribution control according to the measured value of the characteristic parameters of the thermal stress ellipsoid, improve the thermal lens, reduce the sensitivity of the resonant cavity and improve the output power of the laser. And the direction of a stress main shaft can be controlled, the gain loss of the oscillation polarization laser is optimized, the high-power polarization laser output is realized, and the current situation that the polarization output cannot be realized by the existing Tm-YAG crystal is broken through.
Description
Technical Field
The invention relates to the technical field of laser, in particular to a device and a method for measuring thermal stress in a high-power laser cavity.
Background
The 2-micron laser band is a human eye safety band, and has wide application in the fields of meteorological monitoring, laser ranging, laser radar, remote sensing, medical treatment, life science and the like, and researchers of the American national space agency, American air force laboratories, Nuoge company, Stanford university, Harvard university, Cambridge university, Russian academy, European space and the like carry out technical attack on the laser band. The Tm is that the YAG crystal has the most development potential for generating 2 mu m wave band laser by virtue of the advantages of high hardness, high thermal conductivity, excellent mechanical property, thermal property, optical property and the like, but due to the serious thermal effect, a laser is extremely sensitive to the parameters of a resonant cavity (micro-variation of the cavity length of the resonant cavity, pumping power density and the like), the power is improved and limited, and high beam quality and polarized laser output are difficult to realize, so that the Tm is one of the technical difficulty and hot spots of various research institutions at present. Under the high power density pumping state, the internal thermal stress of the gain medium is not distributed in an axisymmetric way as under the ideal state, but in a complex distribution state. The existing laser medium thermal stress research technology is mainly thermal stress numerical simulation based on a finite element method, provides a theoretical research method for thermal effect analysis, and has the limitation that the error is large, and the thermal stress distribution condition cannot be accurately measured.
Disclosure of Invention
The present invention provides a device and a method for measuring thermal stress in a high power laser cavity to solve at least one of the above technical problems.
In a first aspect, the present invention provides a thermal stress measuring device in a high power laser cavity, for measuring a thermal stress distribution in a target region of a gain medium of a laser gain module, the measuring device comprising: a gain laser detection compensation system and a detection light detection compensation system;
the gain laser detection compensation system comprises a laser high-reflection mirror, a laser output mirror, a laser polaroid and a power meter, wherein the power meter comprises a first power meter and a second power meter;
the detection light detection compensation system includes: the device comprises a detection light source, a detection light polarizer, a first detection light wave plate, a spectroscope, a second detection light 1/4 wave plate, a detection light analyzer and a CCD array;
the detection light source, the detection light polarizer, the first detection light 1/4 wave plate, the laser high-reflection mirror, the laser gain module, the laser output mirror and the spectroscope are arranged in sequence; the spectroscope is plated with a dichromatic film system and is used for separating gain laser generated by the laser gain module from detection laser emitted by the detection light source and transmitting the gain laser and the detection laser in two paths, wherein the first path is a gain laser transmission path, and the second path is a detection light transmission path;
on a gain laser transmission path, a laser polarizing film is arranged behind the spectroscope in a coaxial manner and used for dividing gain laser into two s light and p light which are perpendicular to each other; the first power meter is arranged along the direction of an s light emergent light path, and the second power meter is arranged along the direction of a p light emergent light path;
on the detection light transmission path, the second detection light 1/4 wave plate, the detection light analyzer and the CCD array are coaxially placed behind the beam splitter in sequence.
Optionally, the first probe light 1/4 wave plate and the second probe light 1/4 wave plate are both disposed at an angle of 45 ° with respect to the p-light and s-light directions.
Optionally, the laser high-reflection mirror is plated with a dichromatic film system with the gain laser reflectivity of more than 90% and the detection laser transmissivity of more than 80%;
the laser output mirror is coated with a dichroic film system having a transmittance for gain laser light of R and a transmittance for probe laser light of more than 80%.
Optionally, the device further comprises a controller in communication with the CCD array;
the detection light source emits detection laser, the detection laser is changed into linearly polarized light after passing through the detection light polarizer, and the linearly polarized light generates lambda/4 phase difference after passing through the first detection light 1/4 wave plate; after the detection laser is transmitted by the laser high-reflection mirror, the detection laser vertically enters the laser gain module, and the included angle between the detection laser polarization direction and the main stress axis of the laser gain medium is marked as theta; after the detection laser is transmitted by the laser gain medium, phase difference alpha is generated; the laser beam is transmitted by the laser output mirror and reflected by the spectroscope in sequence, then is transmitted to a second detection light 1/4 wave plate and a detection light analyzer along a detection light transmission path, and finally is received by the CCD array; the angle of the second detection light 1/4 wave plate is rotated to obtain n groups of light intensity values of the CCD array, the controller is used for receiving the light intensity values of the CCD array and obtaining values of theta and alpha according to a first preset formula, and the first preset formula is as follows:
wherein: i is the light intensity value measured by the CCD array; i isbAs background intensity; i isaAs an intensity value related to configuration and sample; beta is the included angle between the detection light analyzer and the p light direction, and gamma is the second detection light 1-And the included angle between the fast axis of the 4 wave plate and the p light direction.
Optionally, the detection light detection compensation system further includes an angle adjuster, and the angle adjuster is connected to the second detection light 1/4 wave plate and is configured to adjust the second detection light 1/4 wave plate to rotate by a preset angle.
Optionally, the laser gain module, the laser high-reflection mirror and the laser output mirror form a laser resonant cavity to generate and output gain laser, the polarizer divides the gain laser into two s lights and p lights which are perpendicular to each other, and the s lights are transmitted to the first power meter along the direction of the emergent light path; the p light is transmitted to a second power meter along the direction of the emergent light path; the controller is used for receiving the s-ray laser power P measured by the first power meter in real timesAnd P-light laser power P measured by a second power meter in real timep(ii) a Respectively obtaining a stress ellipsoid azimuth angle omega and a stress ellipticity S according to a second preset formula and a third preset formula;
the second predetermined formula is:
the third preset formula is:
wherein theta is an included angle between the p optical axis and the resolving axis.
YAG crystal, and forms a laser resonant cavity with a high-reflection mirror and a polaroid to generate and output laser with a preset wavelength.
Optionally, the laser with the preset wavelength is 2 μm waveband laser.
In another aspect, the present invention provides a method for measuring thermal stress in a high power laser cavity, in which the thermal stress distribution in a target region of a gain medium of a laser gain module is measured by using the apparatus for measuring thermal stress in a high power laser cavity, the method including:
rotating the angle of the second detection light 1/4 wave plate to obtain n groups of CCD array light intensity values;
obtaining an included angle theta between the polarization direction of the detection laser and the main stress axis of the laser gain medium and a value of a phase difference alpha generated after the detection laser is transmitted through the laser gain medium according to a first preset formula, wherein the first preset formula is as follows:
wherein: i is the light intensity value measured by the CCD array; i isbAs background intensity; i isaAs an intensity value related to configuration and sample; beta is the included angle between the detection light analyzer and the p light direction, and gamma is the included angle between the fast axis of the second detection light 1/4 wave plate and the p light direction;
obtaining the s-light laser power P measured by the first power meter in real timesAnd P-light laser power P measured by a second power meter in real timep；
Based on a first formula and s-ray laser power PsP laser power PpAnd obtaining the thermal stress distribution of the gain medium of the laser gain module.
Optionally based on the first formula and the s-ray laser power PsP laser power PpObtaining the thermal stress distribution of the gain medium of the laser gain module comprises the following steps:
respectively obtaining a stress ellipsoid azimuth angle omega and a stress ellipsoid degree S according to a second preset formula and a third preset formula:
the second predetermined formula is:
the third preset formula is:
wherein theta is an included angle between the p optical axis and the decomposition axis;
and obtaining the thermal stress distribution of the gain medium target area of the laser gain module based on the first formula, the second formula and the third formula.
The technical scheme of the invention has the following beneficial technical effects:
the device and the method for measuring the thermal stress in the high-power laser cavity provided by the embodiment of the invention can be used for measuring the thermal stress distribution in the crystal in a gain state in real time. According to the measured value of the thermal stress distribution characteristic, the pumping power distribution can be optimized to realize the control of the thermal stress distribution, the thermal lens is improved, the sensitivity of the resonant cavity is reduced, the output power of the laser is improved under the condition of the prior art, and the laser output with high beam quality and 2 mu m wave band can be realized; on the other hand, the stress main shaft direction is controlled, the gain loss of the oscillation polarization laser is optimized, the high-power polarization laser output can be realized, and the current situation that the existing Tm-YAG crystal cannot realize the polarization output is broken through.
Drawings
Fig. 1 is a schematic structural diagram of a thermal stress measurement apparatus in a high-power laser cavity according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a thermal stress measurement apparatus in a high-power laser cavity of a single laser gain module according to embodiment 1 of the present invention;
fig. 3 is a schematic structural diagram of a thermal stress measurement apparatus in a multi-laser gain module high-power laser cavity according to embodiment 2 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Fig. 1 shows a schematic structural diagram of a thermal stress measuring device in a high power laser cavity according to an embodiment of the present invention, and fig. 1 is a schematic structural diagram of the thermal stress measuring device in the high power laser cavity according to the embodiment of the present invention. The thermal stress measuring device in the high-power laser cavity is used for measuring the thermal stress distribution of a gain medium 1-1 of a laser gain module 1, and comprises a gain laser detection compensation system and a detection light detection compensation system.
The gain laser detection compensation system comprises a laser high-reflection mirror 2, a laser output mirror 3, a laser polaroid 4 and a power meter, wherein the power meter comprises a first power meter 5-1 and a second power meter 5-2.
The detection light detection compensation system comprises a detection light source 6, a detection light polarizer 7, a first detection light 1/4 wave plate 8-1, a spectroscope 9, a second detection light 1/4 wave plate 8-2, a detection light analyzer 10 and a CCD array 11.
The detection light source 6, the detection light polarizer 7, the first detection light 1/4 wave plate, the laser high-reflection mirror 2, the laser gain module 1, the laser output mirror 3 and the spectroscope 9 are sequentially arranged, wherein the spectroscope 9 is plated with a dichroic film system and is used for separating the gain laser 1-5 generated by the laser gain module 1 from the detection laser 6-1 emitted by the detection light source 6 and transmitting the two paths, wherein the first path is a gain laser transmission path, and the second path is a detection light transmission path.
On the transmission path of the gain laser, a laser polarizer 4 is disposed coaxially behind the beam splitter 9 for splitting the gain laser into two s-light and p-light perpendicular to each other. The first power meter 5-1 is arranged along the direction of the s light emergent light path, and the second power meter 5-2 is arranged along the direction of the p light emergent light path.
On the detection light transmission path, the second detection light 1/4 wave plate 8-2, the detection light analyzer 10 and the CCD array 11 are coaxially disposed behind the beam splitter 9 in sequence.
The thermal stress measuring device in the high-power laser cavity can measure the thermal stress distribution in the crystal in a gain state in real time. The detection light is generated by a detection light source and is transmitted by a laser medium, the detection light generates phase difference in two orthogonal directions due to thermal stress, linearly polarized light is changed into elliptically polarized light, an included angle exists between the vertical component of the two orthogonal directions and the main stress axis of the laser medium, after the light is reflected by a spectroscope, the light intensity value of the detection light is obtained by a CCD array, and the included angle value can be obtained; furthermore, the power values of p light and s light are respectively measured by the first power meter and the second power meter, based on the included angle value, the power value of s light obtained by the first power meter and the power value of p light obtained by the second power meter, and according to the measured value of the characteristic parameter of the thermal stress ellipsoid, the distribution of pump power can be optimized to realize the control of thermal stress distribution, the thermal lens is improved, the sensitivity of a resonant cavity is reduced, the output power of a laser is improved under the prior art, and the output of laser with high beam quality and 2 mu m wave band can be realized; on the other hand, the stress main shaft direction is controlled, the gain loss of the oscillation polarization laser is optimized, the high-power polarization laser output can be realized, and the current situation that the existing Tm-YAG crystal cannot realize the polarization output is broken through.
The embodiment of the invention also provides a thermal stress measuring method in the high-power laser cavity, which can be used for measuring the thermal stress distribution of the gain medium 1-1 of the laser gain module 1 by using the thermal stress measuring device in the high-power laser cavity of the embodiment, and comprises the following steps:
rotating the angle of the second detection light 1/4 wave plate to obtain n groups of light intensity values of the CCD array 11;
obtaining an included angle theta between the polarization direction of the detection laser and the main stress axis of the laser gain medium 1-1 and a value of a phase difference alpha generated after the detection laser is transmitted through the laser gain medium 1-1 according to a first preset formula, wherein the first preset formula is as follows:
wherein: i is the light intensity value measured by the CCD array 11；IbAs background intensity; i isaAs an intensity value related to configuration and sample; beta is the included angle between the detection light analyzer 10 and the p light direction, and gamma is the included angle between the fast axis of the second detection light 1/4 wave plate 8-2 and the p light direction;
obtaining the s-light laser power P measured by the first power meter 5-1 in real timesAnd P-ray laser power P measured by a second power meter 5-2 in real timep；
Based on a first formula and s-ray laser power PsP laser power PpAnd obtaining the thermal stress distribution of the gain medium 1-1 of the laser gain module 1.
The background intensity I can be measured under the condition of no loading light sourcebI.e. the background noise of the CCD array. I isaThe light intensity values under different test conditions.
By the method for measuring the thermal stress in the high-power laser cavity, the distribution of the thermal stress in the crystal in the gain state can be measured in real time. According to the measured value of the thermal stress distribution characteristic, the pumping power distribution can be optimized to realize the control of the thermal stress distribution, the thermal lens is improved, the sensitivity of the resonant cavity is reduced, the output power of the laser is improved under the condition of the prior art, and the laser output with high beam quality and 2 mu m wave band can be realized; on the other hand, the stress main shaft direction is controlled, the gain loss of the oscillation polarization laser is optimized, the high-power polarization laser output can be realized, and the current situation that the existing Tm-YAG crystal cannot realize the polarization output is broken through.
Further, based on the first formula and the s-ray laser power PsP laser power PpObtaining the thermal stress distribution of the gain medium of the laser gain module comprises the following steps:
respectively obtaining a stress ellipsoid azimuth angle omega and a stress ellipsoid degree S according to a second preset formula and a third preset formula:
the second preset formula is as follows:
the third preset formula is as follows:
wherein theta is an included angle between the p optical axis and the resolving axis.
The decomposition axis can be a self-defined axis of a measurer, can be coaxial with the p axis or the s axis, and can also be non-coaxial.
The first preset formula, the second preset formula and the third formula can be obtained based on a change rule of a polarization state of light after the light passes through the birefringent crystal, and the thermal stress distribution of the target area of the laser gain medium 1-1 can be obtained according to the first preset formula, the second formula and the third formula.
The 2-micron-band laser in the application refers to laser with the wavelength of 1.9-2.1 microns; high reflectance means a reflectance greater than 90%, and high transmittance means a transmittance greater than 90%.
The thermal stress measuring device in the high power laser cavity of the present invention is described in detail in several embodiments.
Example 1
Fig. 2 is a schematic structural diagram of a thermal stress measurement apparatus in a high-power laser cavity of a single laser gain module according to this embodiment.
The thermal stress measuring device in the high-power laser cavity of the embodiment is used for measuring the thermal stress of the gain medium 1-1 of the laser gain module 1, and the device comprises a gain laser detection compensation system, a detection light detection compensation system and a controller 12.
The laser gain module 1 comprises a laser gain medium 1-1 and a pumping source 1-2, wherein the Tm is a 90mm long Tm: YAG crystal and a side pumping source with the wavelength of 780 nm-790 nm, and the side pumping source with the wavelength of 783nm can be selected.
The gain laser detection compensation system comprises a laser high-reflection mirror 2, a laser output mirror 3, a laser polaroid 4 and a power meter, wherein the power meter comprises a first power meter 5-1 and a second power meter 5-2.
The detection light detection compensation system comprises a detection light source 6, a detection light polarizer 7, a first detection light 1/4 wave plate 8-1, a spectroscope 9, a second detection light 1/4 wave plate 8-2, a detection light analyzer 10 and a CCD array 11.
The controller 12 is connected with the power meter 5-1, the power meter 5-2 and the CCD array 11 through signal lines.
As shown in fig. 2, the detection light source 6, the detection light polarizer 7, the first detection light 1/4 wave plate 8-1, the laser high-reflection mirror 2, the laser gain module 1, the laser output mirror 3, the spectroscope 9 and the laser polarizer 4 are sequentially and coaxially arranged optically; on the detection light transmission path, a second detection light 1/4 wave plate 8-2, a detection light analyzer 10 and a CCD array 11 are coaxially arranged in sequence behind the spectroscope 9.
As shown in fig. 2, the mirror surface of the high-reflection mirror 2 facing the wave deflection 8-1 of the first probe light 1/4 is coated with a 1064nm laser high-transmission film, and the other mirror surface is coated with a 2.07 μm laser high-reflection film with a reflectivity greater than 99%; one side of the laser output mirror 3, which is close to the laser gain medium 1, is plated with a 2.07-micron laser reflection film with the transmittance of 30 percent and a 1064-nm laser high-transmittance film with the transmittance of more than 99 percent, and the other side is plated with a 2.07-micron laser high-transmittance film with the transmittance of more than 99 percent and a 1064-nm laser high-transmittance film with the transmittance of more than 99 percent; the laser polarizing film 4 is a 45-degree polarizing film, is highly transparent to p light and highly reflective to s light, is coaxially arranged behind the spectroscope 9, and is used for dividing the gain laser into two mutually perpendicular s light and p light and realizing high-power amplification output of the p light and the s light; the detection light polarizer 7 is a 1064nm polaroid; the spectroscope 9 is highly reflective to laser with a wavelength of 1064nm and highly transparent to laser with a wavelength of 2.07 mu m, and is used for separating the gain laser 1-5 generated by the laser gain module 1 from the detection laser 6-1 emitted by the detection light source 6 and transmitting the two laser beams in two paths; the detection light analyzer 10 is a 1064nm polarizer. The first power meter 5-1 is arranged along the direction of the s light emergent light path, and the second power meter 5-2 is arranged along the direction of the p light emergent light path.
The working process of the thermal stress measuring device in the high-power laser cavity provided in this embodiment 1 is as follows:
firstly, a detection light source 6 emits detection laser, the detection laser is changed into linearly polarized light after passing through a detection light polarizer 7, and the linearly polarized light generates lambda/4 phase difference after passing through a first detection light 1/4 wave plate 8-1; after being transmitted by the laser high-reflection mirror 2, the detection laser is vertically incident to the laser gain module 1, and the included angle between the polarization direction of the detection laser and the main stress axis of the laser gain medium 1-1 is marked as theta; generating a phase difference alpha after the detection laser is transmitted through the laser gain medium 1-1; the second detection light 1/4 wave plate and the detection light analyzer 10 are transmitted by the laser output mirror 3 and reflected by the spectroscope 9 in sequence and then transmitted along a detection light transmission path, and finally received by the CCD array; rotating the angle of the second detection light 1/4 wave plate to obtain six sets of light intensity values of the CCD array, receiving the light intensity values of the CCD array by the controller 12, and obtaining the values of θ and α according to a first preset formula, where the first preset formula is:
wherein: i is the light intensity value measured by the CCD array 11; I.C. AbAs background intensity; i isaAs an intensity value related to configuration and sample; beta is the included angle between the detection light analyzer 10 and the p light direction, and gamma is the included angle between the fast axis of the second detection light 1/4 wave plate 8-2 and the p light direction.
In this embodiment, the values of θ and α are calculated by measuring six sets of light intensity values, and the calculation efficiency can be improved on the premise of ensuring the calculation accuracy.
Meanwhile, the laser gain module 1, the laser high-reflection mirror 2 and the laser output mirror 3 form a laser resonant cavity to generate and output gain laser, the polarizing film divides the gain laser into two s light and p light which are perpendicular to each other, and the s light is transmitted to the first power meter 5-1 along the direction of an emergent light path; the p light is transmitted to a second power meter 5-2 along the direction of the emergent light path; the controller 12 receives the s-ray laser power P measured by the first power meter 5-1 in real timesAnd the P-ray laser power P measured by the second power meter 5-2 in real timepRespectively obtaining a stress ellipsoid azimuth angle omega and a stress ellipsoid degree S according to a second preset formula and a third preset formula;
the second predetermined formula is:
the third predetermined formula is:
wherein theta is an included angle between the p optical axis and the resolving axis.
The thermal stress distribution of the target region in the laser cavity can be obtained according to the first preset formula, the second formula and the third preset formula, and all calculation processes are performed in the processor 12.
The thermal stress measuring device in the high-power laser cavity has the advantage that the thermal stress distribution of the target area in the crystal in the gain state can be measured in real time. According to the measured value of the characteristic parameter of the thermal stress ellipsoid, the pumping power distribution can be optimized to realize the control of the thermal stress distribution, the thermal lens is improved, the sensitivity of the resonant cavity is reduced, the output power of the laser is improved, and the laser output with high beam quality and 2 mu m wave band can be realized; on the other hand, the stress main shaft direction is controlled, the gain loss of the oscillation polarization laser is optimized, the high-power polarization laser output can be realized, and the current situation that the existing Tm-YAG crystal cannot realize the polarization output is broken through.
Example 2
Fig. 3 is a schematic structural diagram of a thermal stress measurement apparatus in a multi-laser gain module high-power laser cavity according to this embodiment.
The thermal stress measuring device in the high-power laser cavity of the embodiment is used for measuring the thermal stress of the gain medium 1-1 of the laser gain module 1, and the device comprises a gain laser detection compensation system, a detection light detection compensation system and a controller 12.
The laser gain module 1 comprises a laser gain medium 1-1 and pump sources 1-2, wherein the Tm is 70mm long, YAG crystal and side pump sources with the wavelength of 975nm are arranged in the embodiment, and the number of the laser gain modules 1 is 2.
The gain laser detection compensation system comprises a laser high-reflection mirror 2, an optically active crystal 13, a laser output mirror 3, a laser polaroid 4 and power meters, wherein the power meters comprise a first power meter 5-1 and a second power meter 5-2.
The detection light detection compensation system comprises a detection light source 6, a detection light polarizer 7, a first detection light 1/4 wave plate 8-1, a spectroscope 9, a second detection light 1/4 wave plate 8-2, a detection light analyzer 10 and a CCD array 11.
The controller 12 is connected with the power meter 5-1, the power meter 5-2 and the CCD array 11 through signal lines.
As shown in fig. 3, the detection light source 6, the detection light polarizer 7, the first detection light 1/4 wave plate 8-1, the laser high-reflection mirror 2, the two laser gain modules 1 and the optically active crystal 13 therebetween, the laser output mirror 3, the beam splitter 9 and the laser polarizer 4 are sequentially and coaxially arranged optically; on the detection light transmission path, a second detection light 1/4 wave plate 8-2, a detection light analyzer 10 and a CCD array 11 are coaxially arranged in sequence behind the spectroscope 9.
As shown in fig. 3, the mirror surface of the first probe light 1/4 wave plate 8-1 on the 2-face of the high-reflection mirror is plated with a 532.8nm laser high-transmittance film, and the mirror surface on the other side is plated with a 2.02 μm laser high-reflection film with a reflectivity of more than 99%; the laser output mirror 3 is coated with a dichroic film system with a transmittance for gain laser light of R and a transmittance for detection laser light of more than 80%, and the specific R value is determined by those skilled in the art according to actual needs, for example, one side close to the laser gain medium 1 is coated with a 2.02 μm laser reflection film with a transmittance of 35% and a 532.8nm laser high-transmittance film with a transmittance of more than 99%, and the other side is coated with a 2.02 μm laser high-transmittance film with a transmittance of more than 99% and a 1064nm laser high-transmittance film with a transmittance of more than 99%; the laser polarizing film 4 is a 45-degree polarizing film, is highly transparent to p light and highly reflective to s light, is coaxially arranged behind the spectroscope 9, and is used for dividing the gain laser into the p light and the s light which are perpendicular to each other and realizing high-power amplification output of the p light and the s light; the detection light polarizer 7 is a 532.8nm laser polaroid; the spectroscope 9 is highly reflective to laser with wavelength of 532.8nm and highly transparent to laser with wavelength of 2.02 mu m, and is used for separating the gain laser 1-5 generated by the laser gain module 1 from the detection laser 6-1 emitted by the detection light source 6 and transmitting the gain laser and the detection laser in two paths; the detection light analyzer 10 is a 532.8nm polarizing plate. The first power meter 5-1 is arranged along the direction of the s light emergent light path, and the second power meter 5-2 is arranged along the direction of the p light emergent light path.
The working process of the thermal stress measuring device in the high-power laser cavity provided by the embodiment is as follows:
firstly, a detection light source 6 emits detection laser, the detection laser is changed into linearly polarized light after passing through a detection light polarizer 7, and the linearly polarized light generates lambda/4 phase difference after passing through a first detection light 1/4 wave plate 8-1; after being transmitted by the laser high-reflection mirror 2, the detection laser vertically enters the two laser gain modules 1 and the optically active crystal 13 between the two laser gain modules, and the included angle between the polarization direction of the detection laser and the main stress axis of the laser gain medium 1-1 is marked as theta; after the detection laser is transmitted through the laser gain medium 1-1, a phase difference alpha is generated; the second detection light 1/4 wave plate and the detection light analyzer 10 are transmitted by the laser output mirror 3 and reflected by the spectroscope 9 in sequence and then transmitted along a detection light transmission path, and finally received by the CCD array; rotating the angle of the second detection light 1/4 wave plate to obtain 8 sets of light intensity values of the CCD array, receiving the light intensity values of the CCD array by the controller 12, and obtaining the values of θ and α according to a first preset formula, where the first preset formula is:
wherein: i is the light intensity value measured by the CCD array 11; i isbAs background intensity; i isaAs an intensity value related to configuration and sample; beta is the included angle between the detection light analyzer 10 and the p light direction, and gamma is the included angle between the fast axis of the second detection light 1/4 wave plate 8-2 and the p light direction.
Meanwhile, the laser gain module 1, the laser high-reflection mirror 2 and the laser output mirror 3 form a laser resonant cavity to generate and output gain laser, the polarizing film divides the gain laser into two s light and p light which are perpendicular to each other, and the s light is transmitted to the first power meter 5-1 along the direction of an emergent light path; the p light is transmitted to a second power meter 5-2 along the direction of the emergent light path; the controller 12 receives the s-ray laser power P measured by the first power meter 5-1 in real timesAnd the P-ray laser power P measured by the second power meter 5-2 in real timep，
Respectively obtaining a stress ellipsoid azimuth angle omega and a stress ellipsoid degree according to a second preset formula and a third preset formula; the second predetermined formula is:
the third preset formula is:
wherein Ω is an azimuth angle of elliptically polarized light; theta is the angle between the p optical axis and the resolving axis.
The thermal stress distribution in the laser cavity can be obtained according to the first preset formula, the second preset formula and the third preset formula, and all calculation processes are performed in the processor 12.
The detection light detection compensation system of this embodiment further includes an angle adjuster, and the angle adjuster is connected with second detection light 1/4 wave plate for adjust second detection light 1/4 wave plate and rotate preset angle.
The device and the method for measuring the thermal stress in the high-power laser cavity have the advantages that the thermal stress distribution of the target area in the crystal in the gain state can be measured in real time. According to the measured value of the characteristic parameter of the thermal stress ellipsoid, the pumping power distribution can be optimized to realize the control of the thermal stress distribution, the thermal lens is improved, the sensitivity of the resonant cavity is reduced, the output power of the laser is improved, and the laser output with high beam quality and 2 mu m wave band can be realized; on the other hand, the stress main shaft direction is controlled, the gain loss of the oscillation polarization laser is optimized, the high-power polarization laser output can be realized, and the current situation that the existing Tm-YAG crystal cannot realize the polarization output is broken through.
It should be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (7)
1. A thermal stress measuring device in a high power laser cavity for measuring a thermal stress distribution in a target region of a gain medium (1-1) of a laser gain module (1), said measuring device comprising: a gain laser detection compensation system and a detection light detection compensation system;
the gain laser detection compensation system comprises a laser high-reflection mirror (2), a laser output mirror (3), a laser polaroid (4) and a power meter, wherein the power meter comprises a first power meter (5-1) and a second power meter (5-2);
the detection light detection compensation system includes: the device comprises a detection light source (6), a detection light polarizer (7), a first detection light 1/4 wave plate (8-1), a spectroscope (9), a second detection light 1/4 wave plate (8-2), a detection light analyzer (10) and a CCD array (11);
the detection light source (6), the detection light polarizer (7), the first detection light 1/4 wave plate (8-1), the laser high-reflection mirror (2), the laser gain module (1), the laser output mirror (3) and the spectroscope (9) are sequentially arranged; the spectroscope (9) is plated with a dichroic film system and is used for separating gain laser (1-5) generated by the laser gain module (1) from detection laser (6-1) emitted by the detection light source (6) and transmitting the gain laser and the detection laser in two paths, wherein the first path is a gain laser transmission path, and the second path is a detection light transmission path;
on the transmission path of the gain laser, the laser polarizer (4) is coaxially arranged behind the spectroscope (9) and is used for dividing the gain laser (1-5) into two s light and p light which are perpendicular to each other; the first power meter (5-1) is placed along the direction of an s light emergent light path, and the second power meter (5-2) is placed along the direction of a p light emergent light path;
on a detection light transmission path, the second detection light 1/4 wave plate (8-2), the detection light analyzer (10) and the CCD array (11) are sequentially arranged behind the spectroscope (9) in a coaxial manner;
the measuring device further comprises a controller (12), wherein the controller (12) is connected with the CCD array (11) in a communication mode;
the detection light source (6) emits detection laser, the detection laser is changed into linearly polarized light after passing through the detection light polarizer (7), and the linearly polarized light generates lambda/4 phase difference after passing through a first detection light 1/4 wave plate (8-1); after being transmitted by the laser high-reflection mirror (2), the detection laser vertically enters the laser gain module (1), and the included angle between the polarization direction of the detection laser and the main stress axis of the laser gain medium is marked as theta; after the detection laser is transmitted by the laser gain medium (1-1), a phase difference alpha is generated; the laser beam is transmitted by the laser output mirror (3) and reflected by the spectroscope (9) in sequence, then transmitted to the second detection light 1/4 wave plate (8-2) and the detection light analyzer (10) along a detection light transmission path, and finally received by the CCD array (11); the angle of the second detection light 1/4 wave plate (8-2) is rotated to obtain n groups of light intensity values of the CCD array (11), the controller (12) is used for receiving the light intensity values of the CCD array (11) and obtaining the values of theta and alpha according to a first preset formula, and the first preset formula is as follows:
wherein: i is the light intensity value measured by the CCD array (11); i isbAs background intensity; i isaAs an intensity value related to configuration and sample; beta is the included angle between the detection light analyzer (10) and the p light direction, and gamma is the included angle between the fast axis of the second detection light 1/4 wave plate (8-2) and the p light direction;
the laser gain module (1), the laser high-reflection mirror (2) and the laser output mirror (3) form a laser resonant cavity to generate and output gain laser, the polaroid (4) divides the gain laser into two s lights and p lights which are vertical to each other, and the s lights are transmitted to the first power meter (5-1) along the direction of an emergent light path; the p light is transmitted to a second power meter (5-2) along the direction of the emergent light path; the controller is used for receiving the second signalS-light laser power P measured by a power meter (5-1) in real timesAnd the P-ray laser power P measured by the second power meter (5-2) in real timep(ii) a Respectively obtaining a stress ellipsoid azimuth angle omega and a stress ellipticity S according to a second preset formula and a third preset formula;
the second preset formula is as follows:
the third preset formula is as follows:
wherein theta is an included angle between the p optical axis and the resolving axis.
2. The thermal stress measurement device in the high power laser cavity as claimed in claim 1, wherein the initial positions of the first probe light 1/4 wave plate (8-1) and the second probe light 1/4 wave plate (8-2) are both disposed at an angle of 45 ° with respect to the p-light and s-light directions.
3. A thermal stress measuring device in a high power laser cavity according to claim 1, characterized in that said laser highly reflecting mirror (2) is coated with a dichroic film system having a reflectivity of more than 90% for said gain laser and a transmissivity of more than 80% for said probe laser;
the laser output mirror (3) is coated with a dichromatic film system with the transmittance R for gain laser and the transmittance more than 80% for detection laser.
4. The thermal stress measurement device in a high power laser cavity according to claim 1, wherein said probe light detection compensation system further comprises an angle adjuster, said angle adjuster is connected to said second probe light 1/4 wave plate (8-2) for adjusting rotation of said second probe light 1/4 wave plate (8-2) by a predetermined angle.
5. A thermal stress measuring device in a high power laser cavity according to any of claims 1 to 3, wherein the gain medium (1-1) of the laser gain module (1) is a Tm: YAG crystal, and forms a laser resonator with the high reflection mirror (2) and the polarizer (4) to generate and output laser light with a preset wavelength.
6. The thermal stress measurement device in a high power laser cavity according to claim 5, wherein the laser of the predetermined wavelength is a 2 μm band laser.
7. A method for measuring thermal stress in a high power laser cavity, wherein a thermal stress distribution of a target region of a gain medium (1-1) of a laser gain module (1) is measured by using the device for measuring thermal stress in a high power laser cavity as claimed in claim 1, the method comprising:
rotating the angle of the second detection light 1/4 wave plate (8-2) to obtain n groups of light intensity values of the CCD array (11);
obtaining an included angle theta between the polarization direction of the detection laser and the main stress axis of the laser gain medium (1-1) and a value of a phase difference alpha generated after the detection laser is transmitted through the laser gain medium (1-1) according to a first preset formula, wherein the first preset formula is as follows:
wherein: i is the light intensity value measured by the CCD array (11); i isbAs background intensity; i isaIntensity values related to configuration and sample; beta is the included angle between the detection light analyzer (10) and the p light direction, and gamma is the included angle between the fast axis of the second detection light 1/4 wave plate (8-2) and the p light direction;
obtaining the s-ray laser power P measured by the first power meter (5-1) in real timesAnd the P-ray laser power P measured by the second power meter (5-2) in real timep；
Respectively obtaining a stress ellipsoid azimuth angle omega and a stress ellipsoid degree S according to a second preset formula and a third preset formula:
the second preset formula is as follows:
the third preset formula is as follows:
wherein theta is an included angle between the p optical axis and the decomposition axis;
and obtaining the thermal stress distribution of the target area of the gain medium (1-1) of the laser gain module (1) based on the first preset formula, the second preset formula and the third preset formula.
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