An all-solid-state, tune-free slab laser based on orthogonal Pohr prisms

Abstract

This invention discloses an all-solid-state, tune-free slab laser based on orthogonal Porro prisms, belonging to the field of solid-state laser technology. A diode array is used as the pump source; a pump shaping system homogenizes and shapes the slow axis of the diode array; a coupling cavity mirror introduces the shaped light field into the slab laser crystal and also functions as an oscillating laser reflector; the prisms of the first and second Porro prisms are orthogonal; the light field introduced into the slab laser crystal reaches the first Porro prism via a polarizer, is reflected, and then enters the coupling cavity mirror via the polarizer. It oscillates multiple times back and forth between the end face of the coupling cavity mirror and the end faces of the longitudinally arranged first and second reflectors, reaching the second Porro prism, and then returning along the same path to the first Porro prism, where it is output by the polarizer. This invention can output large single-pulse energy based on a single resonant cavity, eliminating the need for cascaded amplification, resulting in a highly compact system with high photoelectric conversion efficiency.

Description

Technical Field

[0001] This invention belongs to the field of solid-state laser technology, specifically relating to an all-solid-state, adjustment-free slab laser based on orthogonal Porro prisms. Background Technology

[0002] Laser-induced breakdown spectroscopy (LIBS) is an atomic emission spectrometry technique that enables rapid chemical analysis of various materials, helping to determine the elemental composition of diverse samples. LIBS focuses short-energy and high-energy laser pulses onto the surface of a target sample, generating a plasma. The extremely high temperature of this plasma causes the ablated material to dissociate into excited atoms and ions. Because plasma generation depends on a nonlinear process, the repeatability of LIBS measurements is directly related to laser performance. Fluctuations in laser parameters (such as pulse energy and beam quality) lead to changes in ablation quality and plasma temperature, which are reflected in the plasma emission spectrum and may result in inaccurate analyses.

[0003] To achieve high efficiency, compact system design, and broad environmental adaptability in plasma excitation, lasers often require air cooling, high efficiency, high beam quality, and large single-pulse energy. However, traditional rod lasers suffer from severe thermally induced birefringence and depolarization issues under high-power pumping, often requiring additional optical components for suppression. To achieve large single-pulse energy, cascaded amplification is often necessary, resulting in poor system compactness. Pumping is often based on fiber-coupled diode modules, leading to relatively low photoelectric conversion efficiency.

[0004] To achieve higher single-pulse energy, high-power solid-state lasers often require high pump power, resulting in significant thermal effects in the laser medium. This can easily lead to phenomena such as thermally induced birefringence, thermal depolarization loss, and optical thermal distortion. In practical engineering applications, linearly polarized lasers are often required. However, the thermal depolarization effect caused by thermally induced birefringence in high-energy solid-state lasers is quite significant. When linearly polarized light oscillates and propagates back and forth in the resonant cavity, the thermally induced birefringence effect of the gain medium causes the laser polarization state to degrade. This not only affects the polarization state of the output laser but also greatly reduces the output laser energy, significantly impacting the output performance and beam quality of the solid-state laser.

[0005] Porro prisms possess self-collimating properties. Even if the incident laser is incident on the Porro prism at a certain angle, as long as the incident laser satisfies the total internal reflection condition inside the Porro prism, the reflected beam will still return parallel to the incident direction. Traditional resonant cavity output mirrors are often achieved using coatings, resulting in poor mechanical and thermal stability of the laser. The beam quality is easily affected by external vibrations or temperature. Therefore, compared to traditional resonant cavities, if Porro prisms are used as laser resonant cavity mirrors, laser output can still be achieved even when the laser is subjected to impact, vibration, and cavity mirror misalignment, exhibiting excellent mechanical stability. This is widely used in military and space laser fields. However, existing Porro prism resonant cavities are often based on Zigzag multi-pass round-trip gain crystals. Under high-power pumping, edge effects in the width direction of the slab, uneven welding, and defects in the large-area total internal reflection coating can still cause depolarization losses. Furthermore, the manufacturing process is complex and costly. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an all-solid-state, tune-free slab laser based on an orthogonal Pohr prism. It creatively combines the end-pumped slab gain medium with the orthogonal Pohr prism resonator, achieving high single-pulse energy output under high-power pumping. It eliminates the one-dimensional thermally induced birefringence effect, exhibits excellent detuning resistance of the resonator, and provides high beam quality. This makes it widely applicable to harsh environments such as handheld LIBS systems where high-performance lasers are required.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] An all-solid-state, tune-free slab laser based on orthogonal Pohr prisms includes a diode array, a pump shaping system, a coupling cavity mirror, a slab laser crystal, a polarizer, a Q-switching switch, a first Pohr prism, a first reflector, a second reflector, and a second Pohr prism.

[0009] The diode array serves as a pump source;

[0010] The pump shaping system is used to homogenize and shape the slow axis direction of the diode array.

[0011] The coupling cavity mirror is used to introduce the shaped light field into the slab laser crystal, and also serves as an oscillating laser reflector;

[0012] The first and second reflectors are located behind the slab laser crystal and are arranged longitudinally.

[0013] The edges of the first Porro prism and the second Porro prism are orthogonal to each other;

[0014] The coupling cavity mirror, the first reflecting mirror, the second reflecting mirror, the first Porro prism, and the second Porro prism together constitute a highly mechanically stable resonant cavity. The light field introduced into the slab laser crystal reaches the first Porro prism through the polarizer, is reflected, and then enters the coupling cavity mirror through the polarizer. It oscillates back and forth multiple times on the end face where the coupling cavity mirror is located and the end face where the longitudinally arranged first and second reflecting mirrors are located, reaching the second Porro prism, and then returning to the first Porro prism along the same path, and is output by the polarizer.

[0015] The Q-switching switch is used to adjust the ratio of the oscillating laser entering the resonant cavity to the output laser output from the polarizer.

[0016] Furthermore, the laser also includes a 0.57λ waveplate and a first optical wedge arranged sequentially between the Q-switching switch and the first Porro prism; and a λ / 4 waveplate and a second optical wedge located in front of the second Porro prism.

[0017] Furthermore, the first and second optical wedges are used to tune the resonant cavity, and the 0.57λ waveplate and λ / 4 waveplate are used to compensate for the laser depolarization effect caused by the first and second Porro prisms. The polarizer, Q-switching switch, and 0.57λ waveplate together constitute a Q-switching unit.

[0018] Furthermore, the multiple individual diodes are packaged based on bar strips, and the multiple bar strips are stacked vertically to form a diode array, wherein the beam cross-section of the diode array is rectangular.

[0019] Furthermore, the pump shaping system is used to achieve a uniform distribution of the pump light field in the slow axis direction of the diode array, while the fast axis direction has a Gaussian distribution.

[0020] Furthermore, the front surface of the coupling cavity mirror is highly transparent to pump light, and the rear surface is highly transparent to both pump light and highly reflective to oscillating laser.

[0021] Furthermore, the slab laser crystal is a laser gain medium, and the upper and lower surfaces of the slab laser crystal are soldered to a heat sink.

[0022] Furthermore, there is a corresponding relationship between the reflectivity of the polarizer and the voltage applied by the Q-switching switch.

[0023] Furthermore, the Q-switching switch has two states. In the first state, when the Q-switching switch is not working, the polarized laser passes sequentially through the polarizer, the Q-switching switch, and the 0.57λ waveplate before being incident on the first Porro prism. When the laser is reflected again by the first Porro prism to the polarizer, the polarizer's reflectivity is 100%, the resonant cavity loss is at its maximum, and the laser cannot oscillate, thus storing pulse energy. In the second state, when the Q-switching switch is working, the polarizer no longer reflects 100% of the light, but rather partially reflects and partially transmits the light.

[0024] Furthermore, there is a gap between the first and second reflectors, and the pitch angle is less than 0.5°.

[0025] The beneficial effects of this invention are as follows:

[0026] Compared to traditional rod lasers, this invention uses a diode array to directly pump a slab laser crystal, resulting in high photoelectric conversion efficiency. After homogenization along the slow axis of the diode array, part of the end face pumps the slab laser crystal, leading to high coupling efficiency between the pump field and the resonant cavity. Since the slab laser crystal achieves a one-dimensional temperature field distribution, thermally induced birefringence and thermally induced depolarization problems under high-power pumping are eliminated, eliminating the need for additional optical components to suppress heat loss. The output laser linear polarization ratio and beam quality are greatly improved. The diode array can easily achieve higher power pumping based on beam combining, and a large single pulse energy can be output based on a single resonant cavity without the need for cascaded amplification. The system has a very compact size and high photoelectric conversion efficiency.

[0027] Compared to planar output cavity mirrors, the resonant cavity of this invention uses orthogonal Porro prisms, breaking through the concept that this cavity type is only applicable to Zigzag multi-pass structures. However, the laser crystal is partially end-face pumped, resulting in high single-pulse energy, simple processing, greatly reduced cost, high output beam quality, and the ability to meet high-ski mode output requirements. The mechanical stability of the laser is greatly improved, and the conversion efficiency is high.

[0028] The high beam quality of the laser in this invention greatly improves the ability to focus the beam tightly, almost reaching the diffraction limit, which greatly improves the spatial resolution of the LIBS system. The efficient heat dissipation and thermal depolarization elimination allow the laser to operate at a higher repetition frequency, allowing for higher acquisition and scanning speeds. Attached Figure Description

[0029] Figure 1 This is a structural diagram of an all-solid-state, adjustment-free slab laser based on an orthogonal Porro prism according to the present invention.

[0030] Figure label:

[0031] 1. Diode array; 2. Pump shaping system; 3. Coupled cavity mirror; 4. Slab laser crystal; 5. Polarizer; 6. Q-switching switch; 7. 0.57λ waveplate; 8. First optical wedge; 9. First Porro prism; 10. First reflecting mirror; 11. Second reflecting mirror; 12. Second optical wedge; 13. λ / 4 waveplate; 14. Second Porro prism. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] This invention provides an all-solid-state, tune-free slab laser based on orthogonal Porro prisms, designed for handheld LIBS applications. However, its superior output performance extends beyond LIBS applications. Specifically, this invention utilizes a pair of orthogonal Porro prisms to achieve a highly mechanically stable resonant cavity. A slab gain medium is used, and a diode array directly pumps the slab laser crystal without fiber coupling, significantly improving photoelectric efficiency. The diode array undergoes homogenization and shaping, exhibiting a Gaussian distribution along the fast axis and a flat-top distribution along the slow axis, ensuring a one-dimensional temperature field distribution in the slab gain medium. This successfully eliminates thermally induced birefringence and depolarization loss. The pump field is directly injected into the slab laser crystal from its end face, achieving a spatial overlap rate close to that of a fiber-pumped rod crystal, resulting in excellent mode matching. The two large surfaces of the slab laser crystal are soldered to a heat sink, resulting in high heat dissipation efficiency due to the large surface area. The laser field passes directly through the slab laser crystal, and the surface treatment process is simple and reliable. Parasitic oscillations under high-power pumping are greatly suppressed.

[0034] like Figure 1 As shown, the coupling cavity mirror 3, the first reflector 10, the second reflector 11, the first Porro prism 9, and the second Porro prism 14 together constitute a high mechanical stability resonant cavity. The slab laser crystal 4 is the laser gain medium. The upper and lower large surfaces of the slab laser crystal 4 are soldered to the heat sink. The diode array 1 is the pump source. The pump shaping system 2 homogenizes and shapes the slow axis direction of the diode array 1 and injects it directly into the slab laser crystal 4 to ensure that the temperature field inside the slab laser crystal 4 is a one-dimensional temperature field distribution, so as to eliminate thermally induced birefringence and depolarization loss. The fast axis direction of the diode array 1 is still Gaussian distributed, and the pump and oscillating laser modes are well matched. The first reflector 10 and the second reflector 11 are located behind the slab laser crystal 4 and are arranged longitudinally at a certain angle, so that the incident laser can be formed by the coupling cavity mirror 3. The end face of the laser can oscillate back and forth between the longitudinal end face formed by the first reflector 10 and the second reflector 11; the first optical wedge 8 and the second optical wedge 12 finely tune the resonant cavity, and the 0.57λ waveplate 7 and the λ / 4 waveplate 13 compensate for the laser depolarization effect caused by the first Porro prism 9 and the second Porro prism 14. The oscillating laser is output by the polarizer 5. In addition, the polarizer 5, the Q-switching switch 6 and the 0.57λ waveplate 7 together constitute the Q-switching unit. The incident laser entering the resonant cavity through the coupling cavity mirror 3 first enters the polarizer 5, the Q-switching switch 6, the 0.57λ waveplate 7, the first optical wedge 8 and the first Porro prism 9 in sequence, and returns to the resonant cavity along the original optical path and oscillates back and forth multiple times to the second optical wedge 12, the λ / 4 waveplate 13 and the second Porro prism 14, and then returns to the resonant cavity along the original optical path and oscillates back and forth multiple times.

[0035] The diode array 1 serves as the pump source for the slab laser crystal 4. The effective volume of the light-emitting area of ​​a single diode is very small, resulting in limited pump power. Multiple single diodes are packaged based on bars, with a length of approximately 10 mm in the slow axis direction. Dozens of light-emitting areas can be arranged. The light-emitting area of ​​a single diode in the fast axis direction is very small. Collimation output is achieved at a relatively close distance using short-focal-length aspherical cylindrical lenses, resulting in high beam quality. Furthermore, multiple bars are vertically stacked, and the average power can reach thousands of watts. Water-cooled or conduction-cooled vertical bar arrays can be selected. The entire beam cross-section is rectangular, and the cross-section of the slab laser crystal 4 is also rectangular, allowing for efficient matching between the two. Compared to fiber-coupled modules, the diode array 1 directly pumps the slab laser crystal 4, resulting in a simpler and more compact structure and higher photoelectric conversion efficiency.

[0036] The pump shaping system 2 is used to achieve fast and slow axis shaping of the diode array 1. The pump light field in the slow axis direction is uniformly distributed, and the distribution at the edge of the cross-section of the light field distribution is similar to an ideal square wave. The length of the flat top is slightly larger than the slow axis dimension of the slab laser crystal 4. The slab laser crystal 4 has no thermal gradient in the slow axis direction, thus achieving one-dimensional thermal distribution and avoiding thermal depolarization and beam quality degradation. The fast axis direction is Gaussian distributed, generating a thermal lens. Together with the first Porro prism 9 and the second Porro prism 14, a stable resonant cavity is achieved. The pump light field and the resonant cavity achieve good mode matching. The probabilistic failure of some single diodes does not affect the pump shaping effect.

[0037] The front surface of the coupling cavity mirror 3 has a high transmittance of 808nm, and the rear surface has a high transmittance of 808nm and a high reflectance of 1064nm. The diode array 1 is pumped based on the cavity mirror and coupled to the slab laser crystal 4. The front surface of the coupling cavity mirror 3 has a high transmittance of pump light and the rear surface has a high transmittance of pump light and a high reflectance of oscillating laser. The pump light field is introduced and also serves as an oscillating laser reflector.

[0038] The slab laser crystal 4 provides laser gain. The large surface of the crystal is gold-plated and soldered to a copper heat sink, resulting in high heat dissipation efficiency. The laser beam passes directly through the slab laser crystal 4. The surface treatment process is simple and reliable, and parasitic oscillations under high-power pumping are greatly suppressed.

[0039] The polarizer 5 serves three purposes: first, it, together with the Q-switching switch 6 and the 0.57λ waveplate 7, forms a Q-switching switching system; second, it, together with the 0.57λ waveplate 7 and the first Porro prism 9, enables the slab laser crystal 4 to effectively store energy; and third, it, together with the λ / 4 waveplate 13, compensates for the depolarization loss of the second Porro prism 14, allowing linearly polarized laser light to pass through the polarizer 5 without loss.

[0040] At the position of Q-switch 6, there are two states. First, Q-switch 6 is not working. The polarized laser passes sequentially through polarizer 5, Q-switch 6, and 0.57λ waveplate 7 before being incident on the first Porro prism 9. When the laser is reflected again by the first Porro prism 9 to polarizer 5, the reflectivity of polarizer 5 should be 100%, resulting in maximum resonant cavity loss and preventing laser oscillation for pulse energy storage. Polarizer 5 needs to be rotated to 45° with a 0.57λ value to achieve this requirement; λ / 4 and λ / 2 are insufficient. Second, Q-switch 6 is working. Polarizer 5 no longer reflects 100% but partially reflects and partially transmits. There is a corresponding relationship between the reflectivity of polarizer 5 and the voltage applied to Q-switch 6. Selecting an appropriate voltage allows for the selection of a specific reflectivity. The voltage applied to Q-switch 6 is used to adjust the ratio of oscillating laser to output laser.

[0041] The first optical wedge 8 and the second optical wedge 12 are used to finely tune the laser resonant cavity so that the optical axes of all optical elements are located on the same optical reference.

[0042] The first reflector 10 and the second reflector 11 are designed separately with a gap between them. The pitch angle is small, less than 0.5°, which helps to eliminate spontaneous emission under high-power pumping, thereby achieving higher laser pulse energy output.

[0043] The second Porro prism 14 has a 45° angle, and the first Porro prism 9 has a 135° angle. The two prisms are orthogonal to each other. During the laser oscillation process, the reflectivity of polarizer 5 is zero, and the laser oscillation loss is minimized. With the help of other polarization elements in the resonant cavity, the orthogonal placement of the Porro prisms can ultimately achieve effective energy storage and lossless laser oscillation in Q-switched state.

[0044] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fully solid-state, adjustment-free slab laser based on orthogonal Pohr prisms, characterized in that, This includes a diode array, a pump shaping system, a coupling cavity mirror, a slab laser crystal, a polarizer, a Q-switching switch, a first Porro prism, a first reflector, a second reflector, and a second Porro prism, among which... The diode array serves as a pump source; The pump shaping system is used to homogenize and shape the slow axis direction of the diode array, so that the slow axis direction is flat-topped and the fast axis direction is Gaussian, so as to ensure that the temperature field of the slab laser crystal is a one-dimensional temperature field distribution. The coupling cavity mirror is used to introduce the shaped light field into the slab laser crystal, and also serves as an oscillating laser reflector; The first and second reflectors are located behind the slab laser crystal and are arranged longitudinally. The edges of the first Porro prism and the second Porro prism are orthogonal to each other; The coupling cavity mirror, the first reflecting mirror, the second reflecting mirror, the first Porro prism, and the second Porro prism together constitute a highly mechanically stable resonant cavity. The light field introduced into the slab laser crystal reaches the first Porro prism through the polarizer, is reflected, and then enters the coupling cavity mirror through the polarizer. It oscillates back and forth multiple times on the end face of the coupling cavity mirror and the end face of the longitudinally arranged first and second reflecting mirrors before reaching the second Porro prism, and then returns to the first Porro prism via the same path, and is output by the polarizer. There is a gap between the first and second reflecting mirrors, and the pitch angle is less than 0.5° to eliminate spontaneous emission under high-power pumping. The Q-switching switch is used to adjust the ratio of the oscillating laser entering the resonant cavity to the output laser output from the polarizer.

2. The all-solid-state, adjustment-free slab laser based on orthogonal Pohr prisms according to claim 1, characterized in that, The laser also includes a 0.57λ waveplate and a first optical wedge arranged sequentially between the Q-switching switch and the first Porro prism; and a λ / 4 waveplate and a second optical wedge located in front of the second Porro prism.

3. The all-solid-state, adjustment-free slab laser based on orthogonal Pohr prisms according to claim 2, characterized in that, The first and second optical wedges are used to tune the resonant cavity, and the 0.57λ waveplate and λ / 4 waveplate are used to compensate for the laser depolarization effect caused by the first and second Porro prisms. The polarizer, Q-switching switch and 0.57λ waveplate together constitute the Q-switching unit.

4. The all-solid-state, adjustment-free slab laser based on orthogonal Pohr prisms according to claim 1, characterized in that, Multiple individual diodes are packaged based on bar strips, and multiple bar strips are stacked vertically to form a diode array. The beam cross-section of the diode array is rectangular.

5. The all-solid-state, adjustment-free slab laser based on orthogonal Pohr prisms according to claim 1, characterized in that, The front surface of the coupling cavity mirror is highly transparent to pump light, while the rear surface is highly transparent to both pump light and oscillating laser light.

6. The all-solid-state, adjustment-free slab laser based on orthogonal Pohr prisms according to claim 1, characterized in that, The slab laser crystal is used as a laser gain medium, and the upper and lower surfaces of the slab laser crystal are soldered to a heat sink.

7. A solid-state, adjustment-free slab laser based on orthogonal Pohr prisms according to claim 2, characterized in that, There is a corresponding relationship between the reflectivity of the polarizer and the voltage applied by the Q-switching switch.

8. A solid-state, adjustment-free slab laser based on orthogonal Pohr prisms according to claim 7, characterized in that, The Q-switching switch has two states. In the first state, when the Q-switching switch is not working, the polarized laser passes sequentially through the polarizer, the Q-switching switch, and the 0.57λ waveplate before being incident on the first Porro prism. When the laser is reflected back to the polarizer by the first Porro prism, the polarizer's reflectivity is 100%, the resonant cavity loss is at its maximum, and the laser cannot oscillate, thus storing pulse energy. In the second state, when the Q-switching switch is working, the polarizer no longer reflects 100% of the light, but rather partially reflects and partially transmits the light.

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