CN113432837A - Device and method for measuring focal length of crystal thermal lens - Google Patents
Device and method for measuring focal length of crystal thermal lens Download PDFInfo
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- CN113432837A CN113432837A CN202110632694.0A CN202110632694A CN113432837A CN 113432837 A CN113432837 A CN 113432837A CN 202110632694 A CN202110632694 A CN 202110632694A CN 113432837 A CN113432837 A CN 113432837A
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- 239000013078 crystal Substances 0.000 title claims abstract description 125
- 238000000034 method Methods 0.000 title claims abstract description 22
- 238000005086 pumping Methods 0.000 claims abstract description 25
- 238000005259 measurement Methods 0.000 claims abstract description 11
- 230000000694 effects Effects 0.000 claims abstract description 8
- 238000010008 shearing Methods 0.000 claims description 39
- 230000005540 biological transmission Effects 0.000 claims description 4
- 230000005855 radiation Effects 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 claims 1
- 238000010586 diagram Methods 0.000 description 2
- 230000017525 heat dissipation Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910009372 YVO4 Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
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- 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
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- 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
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- Investigating Or Analyzing Materials Using Thermal Means (AREA)
Abstract
The invention discloses a device and a method for measuring the focal length of a crystal thermal lens. The laser crystal to be measured with thermal lens effect and the positive lens with known focal length form a lens group, the position of the positive lens is moved to enable the lens group to become a telescope system, the distance from the laser crystal to the positive lens at the moment is measured, and the focal length of the positive lens is subtracted from the value of the distance to obtain the thermal lens focal length of the measured crystal. The device has simple structure and easy operation, can realize the measurement of the focal lengths of the thermal lenses of the laser crystal in different directions, and can simultaneously perform real-time online measurement on the focal lengths of the thermal lenses of the laser crystal under different pumping powers.
Description
Technical Field
The invention relates to the technical field of laser, in particular to a device and a method for measuring the focal length of a crystal thermal lens.
Background
Laser crystals heat up as they absorb pump radiation, and heat dissipation requires cooling of their surfaces, both of which produce an uneven temperature distribution within the crystal. The temperature change changes the refractive index of the crystal, which causes thermal lens effect, and the laser beam passing through the crystal is distorted, thereby causing the degradation of the beam quality and the conversion efficiency. In order to eliminate the influence of the crystalline thermal lens, an engineer usually uses a lens or a cylindrical lens to compensate the crystalline thermal lens during the design and production of the laser. The matching of the crystal thermal lens and the compensating mirror directly influences the quality of the compensating effect, so that the measurement of the focal length of the crystal thermal lens before compensation has important significance.
Since the focal length of the crystal thermal lens is related to the absorbed pump radiation power, the focal length of the thermal lens is different under different pump powers. At the same pumping power, the inconsistent heat dissipation effects in different directions will bring inconsistent focal lengths of the crystal thermal lenses in different directions. Therefore, in order to achieve a better compensation effect, the focal lengths of the thermal lenses of the laser crystals under different pumping powers need to be measured on line in real time and the focal lengths of the thermal lenses of the laser crystals in different directions under the same pumping power.
To measure the crystalline thermal lens focal length, expert scholars have proposed many different methods. The CCD is used for directly measuring the position of the minimum point of the laser passing through the crystal so as to obtain the focal length of the crystal thermal lens, the method is simple to operate, the result is visual and clear, but the situation that the CCD measuring space is insufficient may exist when the focal length is small, and meanwhile, the method is not suitable for measuring the situation that the focal length of the crystal thermal lens is negative. In the method for measuring the focal length of the crystal thermal lens by adopting the flat cavity, the focal length of the thermal lens under specific pumping power is obtained by monitoring the change of the laser output power, the method can measure the focal length of the crystal thermal lens under different pumping power, but the operation is complicated, and the difference of the crystal thermal lens in each direction cannot be measured. The patent No. ZL201410388115.2 is entitled "measuring method of laser rod thermal lens measuring device", which is characterized in that the focal length of a crystal thermal lens is inverted by comparing and detecting laser power after the crystal is not pumped and is absorbed, the method does not need to move optical elements, is convenient to operate, but the measured crystal pumping mode is limited to side pumping.
Disclosure of Invention
The invention aims to provide a simple and easy-to-operate crystal thermal lens focal length measuring device, and aims to solve the problems that the crystal thermal lens focal length is small and the measurement is difficult under the condition that the crystal thermal lens focal length is negative.
The core idea of the invention is that a laser crystal with thermal lens effect and a positive lens with known focal length form a lens combination, the position of the positive lens is moved to judge that the lens combination is a telescope system by observing interference fringes of a shearing interferometer, and the focal length of the positive lens is subtracted from the distance from the laser crystal to the positive lens measured at the moment to obtain the focal length of the crystal thermal lens.
The technical solution of the invention is as follows:
in one aspect, the present invention provides a device for measuring the focal length of a crystal thermal lens, comprising: a collimated light source and a shearing interferometer; the laser interferometer is characterized by further comprising a positive lens with a known focal length, the laser crystal to be measured, the positive lens and the shearing interferometer are sequentially arranged along the output beam direction of the collimation light source, the thermal lens of the laser crystal to be measured and the positive lens form a telescope system, collimated light beams emitted by the collimation light source are converged or diverged through the laser crystal to be measured, then enter the shearing interferometer through the positive lens to generate interference fringes, and the interference fringes are parallel to the shearing direction.
The function of the collimation light source is to provide collimation laser for the subsequent measurement light path.
The laser crystal to be measured is a crystal which has a thermal lens effect after absorbing pumping radiation, and the pumping mode is end pumping or side pumping.
The positive lens with the known focal length has the function of collimating laser which is diverged or converged after passing through the laser crystal to be measured. When the focal length of the laser crystal thermal lens to be measured is positive, the focal length of the positive lens does not have special requirements and is generally close to or larger than the focal length of the laser crystal thermal lens to be measured. When the focal length of the laser crystal thermal lens to be detected is negative, the focal length of the positive lens needs to be larger than the absolute value of the focal length of the laser crystal thermal lens to be detected.
The shearing interferometer is used for judging whether the laser diverged or converged by the positive lens after passing through the laser crystal to be detected is collimated or not. If the beam is collimated, the interference fringes are parallel to the shearing direction, otherwise they form an angle with the shearing direction.
On the other hand, the invention also provides a method for measuring the focal length of the crystal thermal lens, which is characterized by comprising the following steps:
1) when the focal length of the crystal thermal lens to be detected is positive, selecting the positive lens focal length f to be close to the focal length of the crystal thermal lens to be detected;
when the focal length of the thermal lens of the crystal to be measured is negative, selecting the focal length f of the positive lens to be larger than the absolute value of the focal length of the thermal lens of the crystal to be measured;
2) sequentially placing a laser crystal to be measured, a positive lens and a shearing interferometer along the direction of an output beam of the collimation light source;
3) starting the collimation light source and the shearing interferometer, observing interference fringes obtained on the shearing interferometer, if the direction of the interference fringes is not parallel to the shearing direction, moving the positive lens along the laser transmission direction until the direction of the interference fringes is parallel to the shearing direction, and forming a telescope system by the thermal lens and the positive lens of the laser crystal to be measured;
4) measuring the distance L between the laser crystal to be measured and the positive lens, and calculating the thermal lens focal length f' of the laser crystal to be measured, wherein the formula is as follows:
f′＝L-f。
and further, measuring the focal lengths of the thermal lenses in different directions of the laser crystal to be measured by rotating the shearing direction of the shearing interferometer.
And further, the method also comprises the step of measuring the focal length of the thermal lens of the laser crystal to be measured under different pumping powers, so that the real-time online measurement of the focal length of the thermal lens of the laser crystal to be measured is realized.
If f' is greater than 0, the focal length of the crystal thermal lens is positive, and the thermal lens and the positive lens of the laser crystal to be measured form a Keplerian telescope system. If f' is less than 0, the focal length of the crystal thermal lens is negative, and the thermal lens and the positive lens of the laser crystal to be tested form a Galileo telescope system.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
1. under the condition that the focal length of the crystal thermal lens is small and the focal length of the crystal thermal lens is negative, the laser crystal thermal lens and the positive lens are combined into a telescope system, so that the focal length of the crystal thermal lens can be measured quickly and conveniently.
2. The crystal thermal lens focal length measuring device provided by the invention can be used for measuring the thermal lens focal length generated by end pumping and side pumping.
3. The device for measuring the focal length of the thermal lens of the crystal can measure the focal lengths of the thermal lens of the crystal in different directions.
4. The device for measuring the focal length of the crystal thermal lens can be used for measuring the focal length of the crystal thermal lens on line in real time.
5. The crystal thermal lens focal length measuring device provided by the invention has the advantages of simple structure and convenience in installation and adjustment, and required components can be directly purchased in the market according to requirements without being processed and customized, so that the cost is low.
Drawings
FIG. 1: crystal thermal lens focus is positive, its measuring device and measuring method schematic diagram
FIG. 2: schematic diagram of measuring device and measuring method for crystal thermal lens when focal length is negative
Detailed Description
The technical solutions in the embodiments of the present invention are fully and specifically described below with reference to the accompanying drawings in the embodiments of the present invention.
The first embodiment is as follows: as shown in the attached figure 1, the crystal thermal lens measuring device provided by the invention comprises a collimated light source 1, a laser crystal 2 to be measured, a positive lens 3 with a known focal length and a shearing interferometer 4.
The collimated light source 1 is a He — Ne laser light source. The material of the laser crystal 2 to be detected is Nd: YAG or Nd: YVO4The pumping mode is end pumping or side pumping. The focal length of the positive lens 3 is not specially required, and is generally close to or larger than the focal length of the thermal lens of the laser crystal 2 to be measured。
The specific measurement steps are as follows:
1) and starting the collimation light source 1, converging the emitted collimation laser through the laser crystal 2 to be measured, continuously transmitting the converged laser to the positive lens 3 with the known focal length f, and then entering the shearing interferometer 4.
2) And starting the shearing interferometer 4, observing whether the interference fringes formed on the shearing interferometer are parallel to the shearing direction, if not, moving the position of the positive lens 3 along the light beam transmission direction until the interference fringes are parallel to the shearing direction. At this time, the light beam converged by the laser crystal 2 to be measured is collimated by the positive lens 3, the light beam is output in parallel after passing through the positive lens 3, and the thermal lens of the laser crystal 2 to be measured and the positive lens 3 form a keplerian telescope system.
3) And measuring the distance L from the laser crystal 2 to be measured to the positive lens 3, wherein L is greater than f, and calculating f ═ L-f by using a formula to obtain a value, namely the thermal lens focal length of the laser crystal 2 to be measured.
Example two: as shown in the attached figure 2, the crystal thermal lens measuring device provided by the invention comprises a collimated light source 1, a laser crystal 2 to be measured, a positive lens 3 with a known focal length and a shearing interferometer 4.
The collimated light source 1 is a He — Ne laser light source. The material of the laser crystal 2 to be detected is Nd: YLF or Nd: LiLuF4The pumping mode is end pumping or side pumping. The focal length of the positive lens 3 is larger than the absolute value of the focal length of the thermal lens of the laser crystal 2 to be measured.
The specific measurement steps are as follows:
1) and starting the collimation light source 1, and continuously transmitting the emitted collimation laser after being diverged by the laser crystal 2 to be measured to a positive lens 3 with the known focal length f, and then entering a shearing interferometer 4.
2) And starting the shearing interferometer 4, observing whether the interference fringes formed on the shearing interferometer are parallel to the shearing direction, if not, moving the position of the positive lens 3 along the light beam transmission direction until the interference fringes are parallel to the shearing direction. At this time, the light beam diffused by the laser crystal 2 to be measured is collimated by the positive lens 3, the light beam is output in parallel after passing through the positive lens 3, and the thermal lens of the laser crystal 2 to be measured and the positive lens 3 form a Galileo telescope system.
3) And measuring the distance L from the laser crystal 2 to be measured to the positive lens 3, wherein L is less than f, and calculating f' which is L-f by using a formula to obtain a value, namely the thermal lens focal length of the laser crystal 2 to be measured.
By rotating the shearing direction of the shearing interferometer 4, the crystal thermal lens focal length measuring device provided by the invention can measure the thermal lens focal lengths of the crystal in different directions.
The change of the focal length of the thermal lens of the crystal 2 to be measured is brought when the pumping power is changed, and the focal length of the thermal lens of the crystal under different pumping powers can be obtained by repeating the measuring steps.
Claims (7)
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| CN202110632694.0A CN113432837A (en) | 2021-06-07 | 2021-06-07 | Device and method for measuring focal length of crystal thermal lens |
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Citations (9)
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|---|---|---|---|---|
| US5001718A (en) * | 1989-06-02 | 1991-03-19 | Lumonics, Ltd. | Telescopic thermal lens compensating laser |
| CN1595737A (en) * | 2004-06-25 | 2005-03-16 | 宁波大学 | A laser rod thermal lens effect compensation apparatus and compensation method |
| CN101358898A (en) * | 2008-09-27 | 2009-02-04 | 中国科学院上海光学精密机械研究所 | Measuring device and method for focal length of laser rod positive thermal lens |
| CN101666706A (en) * | 2009-09-07 | 2010-03-10 | 浙江大学 | Device for measuring thermal lens focal length of end-pumped solid-state laser and method |
| CN102684042A (en) * | 2012-05-15 | 2012-09-19 | 清华大学 | Compensation device for thermal lens effect of slab laser |
| CN104111163A (en) * | 2014-07-23 | 2014-10-22 | 中国科学院上海光学精密机械研究所 | Convex lens focal length measuring device and method |
| CN104165754A (en) * | 2014-08-07 | 2014-11-26 | 江苏大学 | Measurement device and method for focal length of laser bar thermal lens |
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2021
- 2021-06-07 CN CN202110632694.0A patent/CN113432837A/en active Pending
Patent Citations (9)
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| CN101358898A (en) * | 2008-09-27 | 2009-02-04 | 中国科学院上海光学精密机械研究所 | Measuring device and method for focal length of laser rod positive thermal lens |
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| CN102684042A (en) * | 2012-05-15 | 2012-09-19 | 清华大学 | Compensation device for thermal lens effect of slab laser |
| CN104111163A (en) * | 2014-07-23 | 2014-10-22 | 中国科学院上海光学精密机械研究所 | Convex lens focal length measuring device and method |
| CN104165754A (en) * | 2014-08-07 | 2014-11-26 | 江苏大学 | Measurement device and method for focal length of laser bar thermal lens |
| CN108226036A (en) * | 2017-12-06 | 2018-06-29 | 西南技术物理研究所 | Integrated laser material fuel factor measuring device based on double grating shear interference |
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