Device and method for real-time thermal focal length measurement of long pulse LDA side-pumped modules

Abstract

This invention discloses a device and method for real-time thermal focal length measurement of a long-pulse LDA side-pump module. The device includes a detector source, a beam expander system, an LDA side-pump module, a knife edge, an energy meter, and a signal generator. The detector source serves as the detection light source for thermal focal length measurement; the beam expander system serves as a beam expander for the detector source size; the LDA side-pump module serves as a heat source generator to achieve high peak power pump injection under long-pulse pumping; the knife edge is placed on both sides of the beam waist position after the detector source passes through the LDA side-pump module to cut the transverse and longitudinal beams, achieving beam size characterization; the energy meter is placed in the rear region of the measurement device to acquire the energy measurement of the detector source; and the signal generator serves as a timing control part to achieve timing synchronization between the detector source and the LDA side-pump module. This invention uses timing synchronization combined with Gaussian beam transmission transformation to obtain the thermal focal length value of the long-pulse LDA side-pump, which has the advantages of simple structure, ease of operation, and high measurement accuracy.

Description

Technical Field

[0001] This invention belongs to the field of laser technology and relates to a device and method for real-time monitoring and measurement of the thermal focal length of a long-pulse LDA side-pumped module. Specifically, it relates to a device and method for real-time thermal lens focal length measurement of a long-pulse LDA side-pumped solid-state laser working medium based on time-series synchronous measurement and control. Background Technology

[0002] With the rapid development of solid-state lasers, numerous high-speed reactive and non-reactive flow field parameter diagnostic technologies have emerged. Simultaneously, high-precision flow field characterization places higher demands on the parametric characteristics of laser sources. Regarding solid-state lasers, semiconductor-pumped solid-state lasers (DPSLs) offer significant advantages over flash lamp-pumped lasers, including better matching of pump light and laser spatial modes and a substantial reduction in thermal effects. Conventional DPSLs employ two pumping methods: end-pumping and side-pumping. End-pumping involves coaxiality between the pump light and the transverse mode of the intracavity laser, resulting in high absorption, low threshold, and high efficiency. However, its limitation lies in its inability to achieve high-power laser output. Therefore, obtaining high-power lasers relies more on high-power long-pulse ring laser diode arrays (LDAs), i.e., the commonly adopted side-pumping structure. The axial cross-section of the pump element determines the pump uniformity, becoming a prerequisite for uniform pump distribution. Complex pump structures result in non-uniform pump light distribution within the working medium. High-power, long-pulse pump light leads to temporal thermal power conversion and thermal deposition within the working medium, generating a thermal gradient distribution within the crystal cross-section. This, in turn, creates thermally induced birefringence and thermal lensing effects, which restrict and affect the output laser performance. In severe cases, self-focusing can occur, causing damage to optical components. Therefore, improving beam quality, compensating for gain distribution, and obtaining high-power stable laser characteristics necessitate real-time monitoring and measurement of temporal thermal focal length.

[0003] To date, the common methods for testing the focal length of thermal lenses are the He-Ne direct measurement method, the transverse mode beat frequency method, and the critical cavity method. These methods can intuitively and clearly characterize the physical meaning and invert the thermal focal length value, but they face problems such as large measurement deviation, cumbersome and complex operation, and inability to achieve real-time synchronous accurate measurement of thermal focal length. Summary of the Invention

[0004] The purpose of this invention is to provide a device and method for real-time thermal focal length measurement of a long-pulse LDA side pump module. It uses time synchronization combined with Gaussian beam transmission transformation to obtain the thermal focal length value of the long-pulse LDA side pump over time, and has the advantages of simple structure, easy operation and high measurement accuracy.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A device for real-time thermal focal length measurement of a long-pulse LDA side-pump module includes a detector source, a beam expander system, an LDA side-pump module, a knife edge, an energy meter, and a signal generator, wherein:

[0007] The detection source serves as the detection light source for thermal focal length measurement;

[0008] The beam expanding system serves as a beam expanding device for the probe source size.

[0009] The LDA side pump module serves as a heat source generating device, enabling high peak power pump injection under long pulse pumping.

[0010] The blade is fixed to the three-dimensional adjustment optical displacement stage and is placed on both sides of the beam waist position after the detection light source passes through the LDA side pump module, cutting the transverse and longitudinal beams to achieve beam size characterization.

[0011] The energy meter is placed in the rear end area of ​​the measuring device and is used to acquire the energy measurement of the detection source;

[0012] The signal generator, as a timing control component, precisely controls the timing distribution to achieve timing synchronization between the detection source and the LDA side pump module.

[0013] A method for real-time thermal focal length measurement of a long-pulse LDA side pump module using the above-mentioned device includes the following steps:

[0014] Step 1: Start the detector source and repeatedly adjust the position of the LDA side pump module to make the reflected light and the incident light coaxial, ensuring that the laser emitted by the detector source coincides with the center of the LDA side pump module;

[0015] Step 2: Set up the signal generator and adjust the delay parameters to ensure that the pumping area under test is synchronized with the detection source in time.

[0016] Step 3: Place the cutting edge on the plane of the high-precision three-dimensional moving stage, and place the entire piece on the slide rail;

[0017] Step 4: Turn on the LDA side-pump module. After the working material absorbs the pump light, thermal deposition is formed inside. Ensure timing control. When the beam is not cut off, measure the output energy parameter E after passing through the LDA side-pump module. Roughly estimate the beam waist position of the probe light source after passing through the LDA side-pump module. Place the knife edge on both sides, fix the knife edge in the x direction, and adjust the y direction position. Record the knife edge movement distance in the y direction when the probe energy is 10%E and 90%E respectively. This distance is the beam size in the y direction. Similarly, the x direction size can be obtained. Adjust the axial movement of the displacement stage to obtain the spot size at different positions.

[0018] Step 5: If the working medium of the LDA-side pump module during pumping is equivalent to a thermal lens, the focal length of the thermal lens corresponding to the pumping region can be calculated using the following formula:

[0019]

[0020] Where i represents the x and y directions; λ is the wavelength of the probe source; l is the distance between the waist of the probe source beam and the center of the LDA side pump module; ω0 is the radius of the waist of the probe source beam; and θ is the beam divergence angle.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The invention has a simple structure and device, is easy to operate, and provides accurate measurement results. It can accurately characterize the thermal focal length parameter at any time within the long-pulse LDA side pump module, providing a basis and possibility for effectively compensating for gain distribution and improving the performance characteristics of output laser. Attached Figure Description

[0023] Figure 1 This is a simplified structural diagram of the real-time thermal focal length measurement device for the long-pulse LDA side pump module of the present invention.

[0024] Figure 2 This is a timing distribution diagram of the real-time thermal focal length measurement device of the long-pulse LDA side pump module of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0026] This invention provides a device for real-time thermal focal length measurement of a long-pulse LDA side pump module, such as... Figure 1 As shown, the device includes a detection source 1, a beam expander system, an LDA side pump module 4, a knife edge 5, an energy meter 6, and a signal generator 7, wherein:

[0027] The detector source 1 is a 532nm pulsed solid-state laser. This device is equipped with an external contact function and is used as a detection light source for thermal focal length measurement.

[0028] The beam expanding system consists of a set of plano-concave lenses 2 and plano-convex lenses 3. The plano-concave lenses 2 diverge the beam propagation direction, and the plano-convex lenses 3 collimate the beam, which is used as a beam expanding system for the size of the detection source.

[0029] The LDA side pump module 4 adopts a seven-sided LDA side pump ring array structure, and the gain medium is rod-shaped Nd:YAG. This pump module can realize high peak power pump injection under long pulse pumping and is used as a heat source generating device.

[0030] The blade 5 is fixed to the three-dimensional adjustable optical displacement stage to cut the transverse and longitudinal beams, thereby achieving beam size characterization.

[0031] The energy meter 6 is placed in the rear end area of ​​the measuring device and is used to obtain the energy measurement of the detection source;

[0032] The signal generator 7 serves as a timing control component, enabling precise control of timing distribution and achieving timing synchronization between the detection source 1 and the LDA side pump module 4.

[0033] In this invention, the repetition rate of the detector source 1 is 1-20Hz, the output energy is 5-10mJ, and the laser divergence angle is 2mrad.

[0034] In this invention, the beam expansion factor of the beam expanding system is 1 to 2 times.

[0035] In this invention, the repetition frequency of the LDA side pump module 4 is 1-20Hz, and the operating time is 2-7ms.

[0036] A method for real-time thermal focal length measurement of a long-pulse LDA side-pump module using the aforementioned device involves precise timing control of the probe source and the LDA side-pump module, combined with the knife-edge method to measure the size distribution of the transmitted light spot in the x and y directions at different positions of the transmitted probe beam after the LDA side-pump module has been operating for different time periods. The beam divergence angle of the probe source after the LDA side-pump module has been obtained based on hyperbolic fitting. The real-time thermal lens focal length distribution in the x and y directions at corresponding time points within the long pulse of the high-power LDA side-pump module's operation is then calculated by combining the transmission transformation characteristics of the Gaussian beam. The characterization of the thermal focal length at different time points can be precisely achieved through timing control. Specifically, the method includes the following steps:

[0037] Step 1: Start the detector source and repeatedly adjust the position of the LDA side pump module to make the reflected light and the incident light coaxial, ensuring that the laser emitted by the detector source coincides with the center of the LDA side pump module;

[0038] Step 2: Set up the signal generator and adjust the delay parameters to ensure that the pumping area under test is synchronized with the detection source in time.

[0039] Step 3: Place the cutting edge on the plane of the high-precision three-dimensional moving stage, and place the entire piece on the slide rail;

[0040] Step 4: Turn on the LDA side-pump module. After the working substance absorbs the pump light, thermal deposition is formed inside. Ensure timing control. When the beam is not cut off, measure the output energy parameter E after passing through the LDA side-pump module. Roughly estimate the beam waist position of the probe light source after passing through the LDA side-pump module. Place the knife edge on both sides, fix the knife edge in the x direction, and adjust the y direction position. Record the knife edge movement distance in the y direction when the probe energy is 10%E and 90%E respectively. This distance is the beam size in the y direction. Similarly, the x direction size can be obtained. Adjusting the axial movement of the displacement stage can obtain the spot size at different positions.

[0041] Step 5: The beam divergence angle θ can be obtained using the following hyperbolic fitting formula:

[0042] ω 2(z)=Az 2 +Bz+C

[0043]

[0044] If the working medium of the LDA-side pump module is equivalent to a thermal lens during pumping, then the focal length of the thermal lens in the x and y directions within the pumping region can be calculated as follows:

[0045]

[0046] Where i represents the x and y directions; λ is the wavelength of the probe source; l is the distance between the waist of the probe source beam and the center of the LDA side pump module; and ω0 is the radius of the waist of the probe source beam.

Claims

1. A method for long pulse LDA side-pumped module real-time thermal focal length measurement, characterized in that The method utilizes a long pulse LDA side pump module real-time thermal focal length measuring device to perform real-time thermal focal length measurement, the device uses time sequence synchronization combined with Gaussian beam transmission transformation to obtain long pulse LDA side pump time thermal focal length values, realizes real-time synchronous thermal focal length precise measurement, obtains high-power stable laser characteristics, and comprises a probe source, a beam expansion system, an LDA side pump module, a knife edge, an energy meter and a signal generator, wherein: The probe source serves as a probe light source for thermal focal length measurement. The beam expansion system serves as a probe source size expansion device. The LDA side pump module adopts a seven-surface LDA side pump ring array structure, and a rod-shaped Nd:YAG is used as a gain medium, the module serves as a heat source generating device, and realizes high peak power pumping injection under long pulse pumping. The knife edge is fixed on a three-dimensional adjustment optical displacement table surface and is placed on both sides of the waist position of the probe light source after the LDA side pump module, cuts the transverse and longitudinal beams, and realizes beam size characterization. The energy meter is placed in the rear end area of the measuring device and is used to obtain probe source energy measurement. The signal generator serves as a time sequence control part, precisely controls time sequence distribution, realizes time sequence synchronization between the probe source and the LDA side pump module, and has the advantages that the method comprises the following steps: Step one, start the probe source, repeatedly adjust the position of the LDA side pump module to make the reflected light coaxial with the incident light, and ensure that the probe light source radiation laser is coincident with the center of the LDA side pump module; Step two, set the signal generator, adjust the delay parameter, and ensure that the pumping region to be measured is time sequence synchronized with the probe source; Step three, place the knife edge on the high-precision three-dimensional moving table plane, and place the whole on the slide rail at the same time; Step four, start the LDA side pump module, the internal heat deposition is formed after the working substance absorbs the pumping light, time sequence control is ensured, the output energy parameter E of the light after the LDA side pump module is measured when the beam is not cut, the beam waist position of the probe light source after the LDA side pump module is roughly estimated, the knife edge is placed on both sides, the x-direction of the knife edge is fixed, the y-direction position is adjusted, and the y-direction knife edge moving distance when the probe energy is 10% E and 90% E is recorded, that is, the beam y-direction size, the x-direction size can be obtained in the same way, and the spot size at different positions can be obtained by adjusting the axial movement of the displacement table; Step five, the working substance of the LDA side pump module under pumping is equivalent to a thermal lens, and the focal length of the thermal lens corresponding to the pumping region is calculated by the following formula: Wherein, i represents the x and y directions; λ is the wavelength of the probe source; l is the distance between the beam waist of the probe source and the center of the LDA side pump module; ω0 is the beam waist radius of the probe light source; θ is the beam divergence angle. The repetition frequency of the probe source is 1-20 Hz, the output energy is 5-10 mJ, and the laser divergence angle is 2 mrad.

2. The method of long-pulse LDA side-pump module real-time thermal focal length measurement of claim 1, wherein The expansion ratio of the beam expansion system is 1-2 times.

3. The method of long-pulse LDA side-pump module real-time thermal focal length measurement of claim 1, wherein The repetition frequency of the LDA side pump module is 1-20 Hz, and the running time is 2-7 ms.

4. The method of long-pulse LDA side-pump module real-time thermal focal length measurement of claim 1, wherein ​

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