All-solid-state debugging-free slab laser based on orthogonal Porro prism

Abstract

The invention discloses an all-solid-state debugging-free slab laser based on an orthogonal Porro prism, and belongs to the technical field of solid laser. The diode stack array is used as a pumping source; the pumping shaping system performs homogenization shaping on the slow axis direction of the diode stack array; the coupling cavity mirror introduces the shaped light field into the lath laser crystal, and is used as an oscillation laser reflector at the same time; the ridges of the first Porro prism and the second Porro prism are mutually orthogonal; a light field introduced into the slab laser crystal reaches the first Porro prism through the polaroid, enters the coupling cavity mirror through the polaroid after being reflected, is subjected to repeated reciprocating oscillation on the end face where the coupling cavity mirror is located and the end face where the first reflector and the second reflector which are longitudinally arranged are located to reach the second Porro prism, and then returns to the first Porro prism along the original path; and the light is output by the polaroid. Large single pulse energy can be output based on a single resonant cavity, cascade amplification is not needed, the system size compactness is very high, and the photoelectric conversion efficiency is high.

Description

Technical Field

[0001] The invention belongs to the technical field of solid lasers, and in particular relates to an all-solid-state adjustment-free slab laser based on an orthogonal Paul prism. Background Art

[0002] Laser-induced breakdown spectroscopy (LIBS) is an atomic emission spectroscopic technique that enables rapid chemical analysis of a wide range of materials and helps determine the elemental composition of a wide range of samples. LIBS focuses short and high-energy laser pulses onto the surface of a target sample to generate a plasma whose extremely high temperature can cause the ablated material to dissociate into excited atoms and ions. Since the generation of plasma depends on nonlinear processes, the repeatability of LIBS measurements is directly related to the laser performance. Fluctuations in laser parameters (such as pulse energy and beam quality) can lead to changes in ablation quality and plasma temperature, which will be reflected in the plasma emission spectrum and may lead to inaccurate analysis.

[0003] In pursuit of high efficiency of plasma excitation, system compactness and wide environmental adaptability, lasers often require air cooling, high efficiency, high beam quality and large single pulse energy; however, the problems of thermally induced birefringence and thermally induced depolarization are more serious under high-power pumping of traditional rod lasers, and additional optical elements are often required to suppress them. In order to achieve large single pulse energy, cascade amplification is often required, the system volume is very poor, the pumping is often based on fiber-coupled diode modules, and the photoelectric conversion efficiency is relatively low.

[0004] In order to achieve a larger single pulse energy, the pump power of high-power solid-state lasers is often high, and the thermal effect of the laser medium is more serious, which can easily cause thermally induced birefringence, thermal depolarization loss, and optical thermal distortion. Linearly polarized lasers are often required in actual engineering applications, and the thermal depolarization effect caused by thermally induced birefringence of high-energy solid-state lasers is more significant. When linearly polarized light oscillates back and forth in the resonant cavity, the thermally induced birefringence effect of the gain medium causes the laser polarization state to degenerate, which not only affects the polarization state of the output laser, but also greatly reduces the output laser energy, greatly affecting the output performance and beam quality of the solid-state laser.

[0005] The Porro prism has the characteristic of self-collimation. 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 light beam will still return parallel to the incident direction. The output cavity mirror of the traditional resonant cavity is often realized by coating. The mechanical stability and thermal stability of the laser are poor, and the beam quality is easily affected by external vibration or temperature. Therefore, compared with the traditional resonant cavity, if the Porro prism is used as the laser resonant cavity mirror, the laser output can still be achieved when the laser is subjected to shock, vibration and cavity mirror misalignment. The mechanical stability is very good and it is widely used in the field of military lasers and space lasers. However, the existing Porro prism resonant cavity is often based on Zigzag multi-pass round-trip gain crystals. The edge effect in the width direction of the slat under high-power pumping, uneven welding, and cooling large-surface total reflection coating defects will still cause depolarization loss, and the processing process is complicated and the cost is high. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides an all-solid-state adjustment-free slab laser based on an orthogonal Porro prism. The end-pumped slab gain medium and the orthogonal Porro prism resonant cavity are creatively combined, and a large single pulse energy output can be achieved under high-power pumping, and the one-dimensional thermally induced birefringence effect is eliminated. The resonant cavity has good anti-detuning characteristics and good beam quality, and can be widely used in harsh application environments such as handheld LIBS to meet the needs of high-performance lasers.

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

[0008] An all-solid-state adjustment-free slab laser based on orthogonal Paul prisms comprises a diode stack, a pump shaping system, a coupling cavity mirror, a slab laser crystal, a polarizer, a Q-switching switch, a first Paul prism, a first reflector, a second reflector, and a second Paul prism, wherein:

[0009] The diode stack array is used as a pump source;

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

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

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

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

[0014] The coupling cavity mirror, the first reflector, the second reflector, the first Porro prism and the second Porro prism together constitute a high mechanical stability resonant cavity. The light field introduced into the slab laser crystal reaches the first Porro prism through the polarizer, and after being reflected, enters the coupling cavity mirror through the polarizer, performs multiple back-and-forth oscillations at the end face where the coupling cavity mirror is located and the end faces where the first reflector and the second reflector are arranged in the longitudinal direction, reaches the second Porro prism, and then returns to the first Porro prism along the original path, and is output by the polarizer;

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

[0016] Furthermore, the laser also includes a 0.57λ wave plate and a first optical wedge arranged in sequence between the Q-switched switch and the first Paul prism; and a λ / 4 wave plate located in front of the second Paul prism and a second optical wedge located in front of the λ / 4 wave plate.

[0017] Furthermore, the first optical wedge and the second optical wedge are used to tune the resonant cavity, the 0.57λ wave plate and the λ / 4 wave plate are used to compensate for the laser depolarization effect caused by the first Por prism and the second Por prism, and the polarizer, the Q-switching switch and the 0.57λ wave plate together constitute a Q-switching unit.

[0018] Furthermore, the plurality of diode single tubes are packaged based on bar strips, and the plurality of bar strips are vertically stacked to form a diode stack array, and the beam cross section of the diode stack is rectangular.

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

[0020] Furthermore, the front surface of the coupling cavity mirror is highly transparent to the pump light, and the rear surface is highly transparent to the pump light and highly reflective to the 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 the heat sink using solder.

[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 is divided into two states. One is that the Q-switching switch is not working, and the polarized laser passes through the polarizer, the Q-switching switch and the 0.57λ wave plate in sequence to be incident on the first Paul prism. When the laser is reflected from the first Paul prism to the polarizer again, the reflectivity of the polarizer is 100%, the loss of the resonant cavity is the largest, the laser cannot oscillate, and pulse energy storage is performed; the other is that the Q-switching switch is working, and the polarizer is no longer 100% reflective, but partially reflective and partially transmissive.

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

[0025] The beneficial effects of the present invention are:

[0026] Compared with the traditional rod laser, the present invention adopts a diode stack array to directly pump the slab laser crystal, which has high photoelectric conversion efficiency. After the slow axis direction of the diode stack is homogenized, part of the end face pumps the slab laser crystal, and the coupling efficiency of the pump light field and the resonant cavity is high. Since the slab laser crystal realizes a one-dimensional temperature field distribution, the problems of thermally induced birefringence and thermally induced depolarization under high-power pumping are eliminated, and no additional optical elements are required to suppress the problem of heat loss. The output laser linear polarization ratio and beam quality are greatly improved. The diode stack array can easily realize higher-power pumping based on the beam combining method, and can output large single pulse energy based on a single resonant cavity without cascade amplification. The system volume is very compact and the photoelectric conversion efficiency is high.

[0027] Compared with the flat output cavity mirror, the resonant cavity of the present invention adopts an orthogonal Paul prism, breaking through the concept that the cavity type is only applicable to the Zigzag multi-pass structure, but the laser crystal adopts partial end-face pumping, the single pulse energy is high, the processing flow is simple, the cost is greatly reduced, the output beam quality is high, and the high base mode output can be met. The mechanical stability of the laser is greatly improved, and the conversion efficiency is high;

[0028] The high beam quality of the laser of the present invention greatly improves the ability of the beam to be tightly focused, almost reaching the diffraction limit, greatly improving the spatial resolution of the LIBS system. Efficient heat dissipation and elimination of thermally induced depolarization enable the laser to operate at a higher repetition frequency, allowing higher acquisition and scanning speeds. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a structural diagram of an all-solid-state adjustment-free slab laser based on an orthogonal Por prism.

[0030] Reference numerals:

[0031] 1. Diode stack; 2. Pump shaping system; 3. Coupled cavity mirror; 4. Slab laser crystal; 5. Polarizer; 6. Q-switch; 7. 0.57λ wave plate; 8. First optical wedge; 9. First Por prism; 10. First reflector; 11. Second reflector; 12. Second optical wedge; 13. λ / 4 wave plate; 14. Second Por prism. DETAILED DESCRIPTION

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

[0033] The present invention provides a fully solid-state, non-adjustable slab laser based on an orthogonal Porro prism, which is dedicated to the laser required for handheld LIBS applications, but the excellent output performance makes the present invention not limited to LIBS applications. Specifically, the present invention realizes a high mechanical stability resonant cavity based on a pair of orthogonal Porro prisms, the gain medium adopts a slab gain medium, the diode stack directly pumps the slab laser crystal without fiber coupling, which greatly improves the photoelectric efficiency, the diode stack is homogenized and shaped, the fast axis direction is Gaussian distribution, the slow axis direction is flat-top distribution, which ensures that the temperature field of the slab gain medium is a one-dimensional temperature field distribution, successfully eliminates thermally induced birefringence and depolarization loss, the pump light field is directly end-face injected into the slab laser crystal, the spatial overlap rate of the pump and laser light fields is close to that of the fiber pump source pumping the rod-shaped crystal, the mode matching is good, the upper and lower large surfaces of the slab laser crystal are soldered to the heat sink using solder, due to the large heat dissipation surface area, high heat dissipation efficiency, the laser light field directly passes through the slab laser crystal, the surface treatment process is simple and reliable, and the parasitic oscillation under high-power pumping is greatly suppressed.

[0034] like Figure 1 As shown, the coupling cavity mirror 3, the first reflector 10, the second reflector 11, the first Por prism 9 and the second Por prism 14 together constitute a high mechanical stability resonant cavity, the slab laser crystal 4 is a laser gain medium, the upper and lower large surfaces of the slab laser crystal 4 are soldered to the heat sink using solder, the diode stack 1 is a pump source, the pump shaping system 2 performs homogenization shaping on the slow axis direction of the diode stack 1, and directly injects the end face 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 to eliminate thermally induced birefringence and depolarization loss, the fast axis direction of the diode stack 1 is still Gaussian distribution, the pump and oscillation 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 in the coupling cavity mirror 3. The end face of the optical cavity can oscillate back and forth between the end face and 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, the 0.57λ wave plate 7 and the λ / 4 wave plate 13 compensate for the laser depolarization effect caused by the first Paul prism 9 and the second Paul prism 14, and the oscillating laser is output by the polarizer 5. In addition, the polarizer 5, the Q-switching switch 6 and the 0.57λ wave plate 7 together constitute a Q-switching unit, wherein 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 wave plate 7, the first optical wedge 8, and the first Paul prism 9 in sequence, returns to the resonant cavity along the original optical path and performs multiple back-and-forth oscillations to reach the second optical wedge 12, the λ / 4 wave plate 13, and the second Paul prism 14, and then returns to the resonant cavity along the original optical path and performs multiple back-and-forth oscillations.

[0035] The diode stack 1 is used as the pump source of the slab laser crystal 4. The effective volume of the light-emitting area of ​​a single diode is very small, and the pump power is limited. Multiple diode single tubes are packaged based on the bar, and the length in the slow axis direction is about 10 mm. The number of light-emitting areas can be arranged in dozens, and the light-emitting area of ​​the diode single tube in the fast axis direction is very small. Based on the short-focus aspheric cylindrical lens, the collimated output is achieved within a relatively close distance, and the beam quality is very high. Further, multiple bars are stacked vertically, and the average power can reach thousands of watts. A water-cooled or conduction-cooled vertical bar array can be used. The cross-section of the entire beam is rectangular, and the cross-section of the slab laser crystal 4 is also rectangular. The two can achieve efficient matching. Compared with the fiber-coupled module, the diode stack 1 directly pumps the slab laser crystal 4, with a simple and compact structure and higher photoelectric conversion efficiency.

[0036] The pump shaping system 2 is used to realize the fast and slow axis shaping of the diode stack array 1. The pump light field in the slow axis direction is evenly distributed. The edge position distribution of the light field distribution cross section is similar to that of an ideal square wave. The flat top length is slightly larger than the slow axis dimension of the slab laser crystal 4. There is no thermal gradient in the slow axis direction of the slab laser crystal 4, thereby realizing one-dimensional thermal distribution, avoiding thermally induced depolarization and beam quality deterioration. The fast axis direction is Gaussian distribution, generating a thermal lens, and cooperating with the first Paul prism 9 and the second Paul prism 14 to realize a stable resonant cavity. The pump light field and the resonant cavity achieve good mode matching, and 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 high transmittance at 808nm, and the rear surface has high transmittance at 808nm and high reflectance at 1064nm. The diode stack array 1 pumps the cavity mirror 3 to couple 3 to the slab laser crystal 4. The front surface of the coupling cavity mirror 3 has high transmittance for pump light, and the rear surface has high transmittance for pump light and high reflectance for oscillating laser. The pump light field is introduced and it 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 welded to a copper heat sink, which has high heat dissipation efficiency. The laser light field directly passes through the slab laser crystal 4. The surface treatment process is simple and reliable, and parasitic oscillations are greatly suppressed under high-power pumping.

[0039] The polarizer 5 has three functions: first, it forms a Q-switching switch system together with the Q-switching switch 6 and the 0.57λ wave plate 7; second, it enables the slab laser crystal 4 to effectively store energy together with the 0.57λ wave plate 7 and the first Paul prism 9; and third, it compensates for the depolarization loss of the second Paul prism 14 together with the λ / 4 wave plate 13 so that the linearly polarized laser passes through the polarizer 5 without loss.

[0040] At the position of Q switch 6, there are two states. One is that Q switch 6 is not working, and the polarized laser passes through polarizer 5, Q switch 6 and 0.57λ wave plate 7 in turn and is incident on the first Paul prism 9. When the laser is reflected from the first Paul prism 9 to polarizer 5 again, the reflectivity of polarizer 5 should be 100%, the loss of the resonant cavity is the largest, the laser cannot oscillate, and pulse energy storage is performed. The polarizer 5 takes 0.57λ and rotates to 45° to achieve the above requirements. Both λ / 4 and λ / 2 cannot meet the requirements. The second is that Q switch 6 is working, and polarizer 5 is no longer 100% reflective, but partially reflective and partially transmissive. There is a corresponding relationship between the reflectivity of polarizer 5 and the voltage applied by Q switch 6. A specific reflectivity can be selected by selecting an appropriate voltage. The voltage applied by Q switch 6 is used to adjust the ratio of oscillating laser and output laser.

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

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

[0043] The edge angle of the second Porro prism 14 is 45°, and the edge angle of the first Porro prism 9 is 135°. The edges of the two are orthogonal to each other. For the laser oscillation process, the reflectivity of the polarizer 5 is equal to zero, and the laser oscillation loss is minimal. In conjunction with other polarization elements in the resonant cavity, the orthogonal arrangement of the Porro prisms can ultimately achieve effective energy storage and lossless laser oscillation in the Q-switched state.

[0044] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is 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 in the scope of protection of the present invention.

Claims

1. An all-solid-state adjustment-free slab laser based on orthogonal Paul prism, characterized in that: It includes a diode stack, a pump shaping system, a coupling cavity mirror, a slab laser crystal, a polarizer, a Q-switching switch, a first Paul prism, a first reflector, a second reflector, and a second Paul prism, wherein: The diode stack array is used as a pump source; The pump shaping system is used to homogenize and shape the slow axis direction of the diode stack; The coupling cavity mirror is used to introduce the shaped light field into the slab laser crystal and is also used as an oscillating laser reflection mirror; The first reflector and the second reflector are located behind the slab laser crystal and are arranged longitudinally; The ridges of the first Porro prism and the second Porro prism are orthogonal to each other; The coupling cavity mirror, the first reflector, the second reflector, the first Porro prism and the second Porro prism together constitute a high mechanical stability resonant cavity. The light field introduced into the slab laser crystal reaches the first Porro prism through the polarizer, and after being reflected, enters the coupling cavity mirror through the polarizer, performs multiple back-and-forth oscillations at the end face where the coupling cavity mirror is located and the end faces where the first reflector and the second reflector are arranged in the longitudinal direction, reaches the second Porro prism, and then returns to the first Porro prism along the original path, and is output by the polarizer; The Q-switching switch is used to adjust the ratio of the oscillating laser light entering the resonant cavity and the output laser light output by the polarizer.

2. The all-solid-state adjustment-free slab laser based on orthogonal Por prism according to claim 1, characterized in that: The laser also includes a 0.57λ wave plate and a first optical wedge which are sequentially arranged between the Q-switching switch and the first Paul prism; and a λ / 4 wave plate in front of the second Paul prism and a second optical wedge in front of the λ / 4 wave plate.

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

4. The all-solid-state adjustment-free slab laser based on orthogonal Por prism according to claim 1, characterized in that: The plurality of diode single tubes are packaged based on a bar, and the plurality of bar are vertically stacked to form a diode stack array, and the beam cross section of the diode stack is rectangular.

5. The all-solid-state adjustment-free slab laser based on orthogonal Por prism according to claim 1, characterized in that: The pump shaping system is used to achieve uniform distribution of the pump light field in the slow axis direction of the diode stack array, and Gaussian distribution in the fast axis direction.

6. The all-solid-state adjustment-free slab laser based on orthogonal Por prism according to claim 1, characterized in that: The front surface of the coupling cavity mirror is highly transparent to the pump light, and the rear surface is highly transparent to the pump light and highly reflective to the oscillating laser.

7. The all-solid-state adjustment-free slab laser based on orthogonal Por prism according to claim 1, characterized in that: The slab laser crystal is a laser gain medium, and the upper and lower surfaces of the slab laser crystal are welded to the heat sink using solder.

8. The all-solid-state adjustment-free slab laser based on orthogonal Por prism 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.

9. The all-solid-state adjustment-free slab laser based on orthogonal Por prism according to claim 8, characterized in that: The Q-switch is divided into two states. One is that the Q-switch is not working, and the polarized laser passes through the polarizer, the Q-switch and the 0.57λ wave plate in sequence to be incident on the first Pau prism. When the laser is reflected from the first Pau prism to the polarizer again, the reflectivity of the polarizer is 100%, the loss of the resonant cavity is the largest, the laser cannot oscillate, and pulse energy storage is performed. The other is that the Q-switch is working, and the polarizer is no longer 100% reflective, but partially reflective and partially transmissive.

10. The all-solid-state adjustment-free slab laser based on orthogonal Por prism according to claim 1, characterized in that: There is a gap between the first reflector and the second reflector, and the pitch angle is less than 0.5°.

Images