Extra-cavity frequency-doubling pulse-width-adjustable ultraviolet laser device and method

Abstract

A half-wave plate and a focusing lens are sequentially arranged on an output light path of a pulse width adjustable infrared laser, the focusing lens is connected with a frequency doubling crystal, the frequency doubling crystal is connected with a frequency tripling crystal, the output end face of the frequency tripling crystal is cut into a Brewster angle, and the output end face of the frequency tripling crystal is connected with a pulse width adjustable infrared laser. The output infrared laser is shielded by the infrared light blocking block after being transmitted in the space, the output green laser is shielded by the green light blocking block after being transmitted in the space, the frequency tripling crystal is connected with the imaging lens, the imaging lens is connected with the input surface of the wedge-shaped lens, and the input surface of the wedge-shaped lens is cut into a Brewster angle. Through fine adjustment of the distance between the imaging lens and the frequency tripling crystal and the distance between the wedge-shaped lens and the imaging lens, the ultraviolet laser output by the wedge-shaped lens becomes circular and is output. The Brewster angle output surface of the frequency tripling crystal reduces the ultraviolet damage probability and separates infrared light, green light and ultraviolet light. The position of the imaging lens is finely adjusted to compensate a light spot ellipse caused by a walk-off effect during frequency doubling.

Description

Technical Field

[0001] The invention relates to an extra-cavity frequency-doubled and pulse-width adjustable ultraviolet laser device and method. Background Art

[0002] With the development of the laser industry, it is difficult for single-parameter lasers to perfectly match processing requirements during use, so lasers with adjustable pulse width have been derived. Compared with picosecond lasers and femtosecond lasers, nanosecond lasers have lower costs, higher output pulse energy, and a wider range of uses. In order to further improve the processing performance of pulse width adjustable lasers, it is necessary to extend the output wavelength of pulse width adjustable lasers from infrared to ultraviolet. Since the pulse width of pulse width adjustable lasers is generated by electrical switch modulation, there is no cavity structure and it is impossible to double the frequency within the cavity. Therefore, the ultraviolet output of pulse width adjustable lasers needs to be carried out by extra-cavity frequency doubling.

[0003] In the laser industry, the peak value of nanosecond lasers is low when they are frequency-doubled outside the cavity. In order to improve the frequency-doubled efficiency, the infrared laser needs to be focused near the doubled and tripled crystals. The infrared light is doubled in turn by the doubled and tripled crystals, and the tripled output is separated according to the different properties of ultraviolet, green light, and infrared to obtain ultraviolet laser output with adjustable pulse width.

[0004] The focus of the prior art is how to improve the damage threshold and beam roundness of the output ultraviolet light beam. The Chinese patent with patent publication number CN117117619A discloses a YAG side-pumped extracavity frequency-doubled ultraviolet laser, which is the most common frequency-doubled method. Its disadvantage is that when the output surface of the tripled frequency crystal is only the coating surface, the output ultraviolet laser spot is small and it is easy to cause damage to the output crystal end face. The Chinese patent with patent publication number CN107315301A discloses an ultrafast laser tripled frequency device and method, which cuts the output end face of the tripled frequency crystal into a Brewster angle, and uses the polarization characteristics of the output light to achieve ultraviolet separation output, reducing the probability of damage to the output end face. The output ultraviolet light beam is shaped into a circle using a wedge mirror, but its disadvantage is that the input light beam is an approximately parallel light beam and is not compatible with a focused light beam. The Chinese patent with the patent publication number CN219321802U discloses a UV laser. In order to improve the damage threshold and beam roundness of the output UV beam, the output end face of the triple frequency crystal is cut into the Brewster angle, and a wedge mirror is added in front of the frequency doubling crystal. The disadvantage is that the compatibility with the focused beam is poor, the focused beam becomes elliptical, and the spot and frequency doubling efficiency cannot be optimized at the same time. The Chinese patent with the patent publication number CN116974120A discloses an ultrafast laser wedge angle beam expansion system. The output UV beam is shaped by the wedge angle beam expansion system. The disadvantage is that it is still not compatible with the beam shaping of the focused beam after the Brewster angle output. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an extra-cavity frequency-doubled and pulse-width adjustable ultraviolet laser device and method.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The extracavity frequency-doubled adjustable pulse width ultraviolet laser device is characterized in that a half wave plate and a focusing lens are arranged in sequence on the output optical path of the pulse width adjustable infrared laser, the focusing lens is connected to a double frequency crystal, the double frequency crystal is connected to a triple frequency crystal, the output end face of the triple frequency crystal is cut into a Brewster angle, the output infrared laser is shielded by an infrared light block after spatial transmission, the output green laser is shielded by a green light block after spatial transmission, the triple frequency crystal is connected to an imaging lens, the imaging lens is connected to the input face of a wedge mirror, and the input face of the wedge mirror is cut into a Brewster angle.

[0008] Furthermore, in the above-mentioned extracavity frequency-doubled adjustable pulse width ultraviolet laser device, the pulse width adjustable infrared laser is an infrared laser with an output wavelength in the 1030nm, 1064nm, and 1342nm bands, an output power of 1 to 500W, and a pulse width of 100fs to 100ns.

[0009] Furthermore, in the above-mentioned extra-cavity frequency-doubled adjustable pulse width ultraviolet laser device, the half-wave plate is an infrared half-wave plate with an operating wavelength in the bands of 1030nm, 1064nm, and 1342nm.

[0010] Furthermore, in the above-mentioned extra-cavity frequency-doubled and pulse-width adjustable ultraviolet laser device, the operating wavelength of the focusing lens is in the 1030nm, 1064nm, and 1342nm bands.

[0011] Furthermore, in the above-mentioned extra-cavity frequency-doubled and pulse-width adjustable ultraviolet laser device, the frequency-doubled crystal is LBO, BBO, or KTP.

[0012] Furthermore, in the above-mentioned extra-cavity frequency-doubled and pulse-width adjustable ultraviolet laser device, the tripled frequency crystal is LBO, BBO, or CLBO.

[0013] Furthermore, in the above-mentioned extracavity frequency-doubled and pulse-width adjustable ultraviolet laser device, the imaging ratio of the imaging lens is less than or equal to 1.

[0014] Furthermore, in the above-mentioned extra-cavity frequency-doubled and pulse-width adjustable ultraviolet laser device, the imaging ratio of the imaging lens is 1:1, 1:0.9 or 1:0.8.

[0015] The invention discloses an extra-cavity frequency-doubling ultraviolet laser method with adjustable pulse width. After the infrared laser with adjustable pulse width outputted by the pulse width adjustable infrared laser passes through a half wave plate, the polarization of the infrared light is adjusted to vertical polarization. The infrared light is focused through a focusing lens, and the focus is located near a frequency doubling crystal and a frequency tripling crystal. By adjusting the front and rear positions of the focusing lens, the distance between the frequency doubling crystal and the frequency tripling crystal, and the temperature of the frequency doubling crystal and the frequency tripling crystal, the output ultraviolet light reaches the strongest. The infrared laser outputted by the frequency tripling crystal is shielded by an infrared light blocking block after spatial transmission, and the outputted green light laser is shielded by a green light blocking block after spatial transmission. An imaging lens is arranged on the propagation path of the output ultraviolet laser, and its imaging object surface corresponds to the Brewster angle output surface of the frequency tripling crystal, and the image surface is located at the input surface of the wedge mirror. By slightly adjusting the spacing between the imaging lens and the frequency tripling crystal and the spacing between the wedge mirror and the imaging lens, the ultraviolet laser outputted by the wedge mirror becomes circular and is output.

[0016] Furthermore, in the above-mentioned extracavity frequency-doubling adjustable pulse width ultraviolet laser method, the light intensity of the infrared laser with adjustable pulse width is enhanced after focusing, and triple frequency output is achieved. The Brewster angle output surface of the triple frequency crystal reduces the probability of ultraviolet damage, and also separates infrared light, green light and ultraviolet light. The separated ultraviolet light is elliptical due to the walk-off effect and the wedge angle output. The wedge mirror shaping ensures that the elliptical ratio of the elliptical spot input to the wedge mirror is approximately equal to the elliptical ratio of the light spot output by the triple frequency crystal. The imaging lens between the triple frequency crystal and the wedge mirror performs imaging operation, which is convenient for shaping. At the same time, the fine adjustment of the imaging lens position is used to compensate for the light spot ellipse caused by the walk-off effect during frequency doubling, while ensuring the output ultraviolet efficiency, avoiding damage and shaping the ultraviolet output into a circular light spot.

[0017] Compared with the prior art, the present invention has significant advantages and beneficial effects, which are specifically embodied in the following aspects:

[0018] The present invention realizes an extracavity frequency-doubled ultraviolet laser with high efficiency and high beam quality by using a method of focusing frequency doubling and shaping output after imaging. By slightly adjusting the distance between the imaging lens and the triple frequency crystal and the distance between the wedge mirror and the imaging lens, the ultraviolet laser output by the wedge mirror is made circular and output. The Brewster angle output surface of the triple frequency crystal reduces the probability of ultraviolet damage and separates infrared light, green light and ultraviolet light. The imaging lens position is finely adjusted to compensate for the spot ellipse caused by the walk-off effect during frequency doubling. The output efficiency is guaranteed, the damage of the device is avoided, and the roundness of the output spot can be maintained at the same time, providing a simple and effective implementation scheme for the same type of extracavity frequency-doubled ultraviolet laser.

[0019] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or be understood by practicing the specific embodiments of the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 : Schematic diagram of the optical path structure of the laser device of the present invention. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0023] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. At the same time, in the description of the present invention, directional terms and order terms are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0024] like Figure 1 As shown, an extracavity frequency-doubled adjustable pulse width ultraviolet laser device, a half wave plate 2 and a focusing lens 3 are arranged in sequence on the output optical path of the pulse width adjustable infrared laser 1, the focusing lens 3 is connected to a double frequency crystal 4, the double frequency crystal 4 is connected to a triple frequency crystal 5, the output end face of the triple frequency crystal 5 is cut into a Brewster angle and is not coated, the output infrared laser is blocked by an infrared light blocking block 6 after spatial transmission, the output green laser is blocked by a green light blocking block 7 after spatial transmission, the triple frequency crystal 5 is connected to an imaging lens 8, the imaging lens 8 is connected to the input face of a wedge-shaped mirror 9, the input face of the wedge-shaped mirror 9 is cut into a Brewster angle and is not coated.

[0025] The pulse width adjustable infrared laser 1 is an infrared laser with an output wavelength in the bands of 1030nm, 1064nm and 1342nm, an output power of 1 to 500W and a pulse width of 100fs to 100ns.

[0026] The half wave plate 2 is an infrared half wave plate with working wavelengths in the 1030nm, 1064nm, and 1342nm bands.

[0027] The working wavelength of the focusing lens 3 is in the 1030nm, 1064nm, and 1342nm bands.

[0028] The double frequency crystal 4 is LBO, BBO, or KTP. The triple frequency crystal 5 is LBO, BBO, or CLBO.

[0029] The imaging ratio of the imaging lens 8 is less than or equal to 1, preferably 1:1, or 1:0.9 or 1:0.8.

[0030] The infrared laser outputted by the adjustable pulse width infrared laser 1 is adjusted to vertical polarization after passing through the half wave plate 2. The infrared light is focused through the focusing lens 3, and the focus is located near the double frequency crystal 4 and the triple frequency crystal 5. The output ultraviolet light reaches the strongest by adjusting the front and rear positions of the focusing lens 3 and the distance between the double frequency crystal 4 and the triple frequency crystal 5 and the temperature of the double frequency crystal 4 and the triple frequency crystal 5. The infrared laser outputted by the triple frequency crystal 5 is shielded by the infrared light blocking block 6 after spatial transmission, and the outputted green light laser is shielded by the green light blocking block 7 after spatial transmission. The imaging lens 8 is arranged on the propagation path of the output ultraviolet laser, and the imaging ratio is 1:1. The object plane of the imaging corresponds to the Brewster angle output surface of the triple frequency crystal 5, and the image plane is located at the input surface of the wedge mirror 9. By slightly adjusting the spacing between the imaging lens 8 and the triple frequency crystal 5 and the spacing between the wedge mirror 9 and the imaging lens 8, the ultraviolet laser outputted by the wedge mirror 9 becomes circular and outputs.

[0031] The infrared laser with adjustable pulse width is focused and the light intensity is enhanced to realize triple frequency output. The Brewster angle output surface of the triple frequency crystal 5 reduces the probability of ultraviolet damage and also separates infrared light, green light and ultraviolet light. The separated ultraviolet light is elliptical due to the walk-off effect and the wedge angle output. The wedge mirror 9 is shaped to ensure that the elliptical ratio of the elliptical spot input by the wedge mirror is approximately equal to the elliptical ratio of the light spot output by the triple frequency crystal. The imaging lens 8 between the triple frequency crystal 5 and the wedge mirror 9 performs imaging operation to facilitate shaping. At the same time, the position of the imaging lens 8 is fine-tuned to compensate for the light spot ellipse caused by the walk-off effect during frequency doubling. While ensuring the output ultraviolet efficiency, it avoids damaging the device and shapes the ultraviolet output into a better circular light spot. The optical path is simple and effective.

[0032] Example

[0033] The output parameters of the pulse width adjustable infrared laser 1 are an average power of 108W, a repetition frequency of 200kHz, an output spot of 2mm, an output pulse width adjustable from 2ns to 7ns, and a fixed pulse width of 5ns. After the infrared light passes through the half wave plate 2, the polarization of the output infrared light is adjusted to vertical polarization, and the infrared light is focused after passing through the focusing lens 3. The focal length of the focusing lens is 250mm, and the focus after focusing is 170μm. The focus is located between the double frequency crystal 4 and the triple frequency crystal 5, close to the double frequency crystal 4. The spacing between the focusing lens 3 and the double frequency crystal 4 is 285mm, and the spacing between the double frequency crystal 4 and the triple frequency crystal 5 is 33mm. The temperature of the double frequency crystal 4 is set to 50℃, and the temperature of the triple frequency crystal 5 is set to 45℃, so that the output ultraviolet light reaches a maximum average power of 44.6W. The infrared laser output by the tripled frequency crystal 5 is blocked by the infrared light blocking block 6 after spatial transmission, and the green laser output is blocked by the green light blocking block 7 after spatial transmission. An imaging lens 8 is set on the propagation path of the output ultraviolet laser. The focal length of the imaging lens 8 is 100mm, and the distance between the imaging lens 8 and the Brewster angle output surface of the tripled frequency crystal 5 is 160mm. The material of the wedge mirror 9 is quartz, and the cutting angle is 56°. The distance between the wedge mirror 9 and the imaging lens 8 is 200mm, and the ultraviolet laser becomes circular and is output.

[0034] The present invention aims to solve the problem that the ultraviolet light beam output by the focused light beam during the frequency doubling outside the cavity of the pulse width adjustable laser is easy to cause damage to the triple frequency crystal and the roundness of the output light beam is not good. The infrared part of the adjustable pulse width laser is kept unchanged, and the output light beam is focused to the vicinity of the double frequency crystal and the triple frequency crystal through a lens. The double frequency crystal is processed by polishing and coating with an anti-reflection film to process the light-transmitting end face, and the incident end face of the triple frequency crystal is processed by polishing and coating with an anti-reflection film. The output end face of the triple frequency crystal is cut to the Brewster angle and is not coated. The infrared light beam and green light output by the triple frequency crystal are blocked, and the ultraviolet output light beam is shaped by a lens and a wedge mirror in turn and then output. The output end face of the triple frequency crystal is cut to the Brewster angle and is not coated, so as to reduce the probability of ultraviolet damage to the output end face, and at the same time, the output infrared light, green light and ultraviolet light are separated by using the different refractive indices of different output wavelengths. After the ultraviolet light is output, it first passes through the lens in order to image the output end face. By using the principle of wedge mirror shaping and combining the imaging light spot, the output beam is fine-tuned into a circle to ensure the consistency of the output.

[0035] In summary, the present invention utilizes the method of focusing frequency doubling and post-imaging shaping output to realize high-efficiency and high-beam-quality extracavity frequency-doubled ultraviolet laser, which not only ensures the output efficiency but also avoids the damage of the device, while maintaining the roundness of the output light spot, providing a concise and effective implementation scheme for the same type of extracavity frequency-doubled ultraviolet laser.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention. It should be noted that similar numbers and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0037] The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0038] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

Claims

1. An extracavity frequency-doubled and pulse-width adjustable ultraviolet laser device, characterized in that: A half wave plate (2) and a focusing lens (3) are sequentially arranged on the output optical path of the pulse width adjustable infrared laser (1); the focusing lens (3) is connected to a frequency doubling crystal (4); the frequency doubling crystal (4) is connected to a frequency trebling crystal (5); the output end face of the frequency trebling crystal (5) is cut to a Brewster angle; the output infrared laser is shielded by an infrared light blocking block (6) after spatial transmission; the output green laser is shielded by a green light blocking block (7) after spatial transmission; the frequency trebling crystal (5) is connected to an imaging lens (8); the imaging lens (8) is connected to an input face of a wedge mirror (9); the input face of the wedge mirror (9) is cut to a Brewster angle.

2. The extracavity frequency-doubled and pulse-width adjustable ultraviolet laser device according to claim 1, characterized in that: The pulse width adjustable infrared laser (1) is an infrared laser with an output wavelength in the 1030nm, 1064nm and 1342nm bands, an output power of 1 to 500W, and a pulse width of 100fs to 100ns.

3. The extracavity frequency-doubled and pulse-width adjustable ultraviolet laser device according to claim 1, characterized in that: The half wave plate (2) is an infrared half wave plate with a working wavelength in the 1030nm, 1064nm and 1342nm bands.

4. The extracavity frequency-doubled and pulse-width adjustable ultraviolet laser device according to claim 1, characterized in that: The working wavelength of the focusing lens (3) is in the 1030nm, 1064nm and 1342nm bands.

5. The extracavity frequency-doubled and pulse-width adjustable ultraviolet laser device according to claim 1, characterized in that: The frequency doubling crystal (4) is LBO, BBO or KTP.

6. The extracavity frequency-doubled and pulse-width adjustable ultraviolet laser device according to claim 1, characterized in that: The triple frequency crystal (5) is LBO, BBO or CLBO.

7. The extracavity frequency-doubled and pulse-width adjustable ultraviolet laser device according to claim 1, characterized in that: The imaging ratio of the imaging lens (8) is less than or equal to 1.

8. The extracavity frequency-doubled and pulse-width adjustable ultraviolet laser device according to claim 7, characterized in that: The imaging ratio of the imaging lens (8) is 1:1, 1:0.9 or 1:0.

8.

9. Extracavity frequency-doubled adjustable pulse width ultraviolet laser method, characterized in that: The infrared laser with adjustable pulse width (1) outputs infrared laser with adjustable pulse width, and after passing through a half wave plate (2), the polarization of the infrared light is adjusted to vertical polarization. The infrared light is focused through a focusing lens (3), and the focus is located near a double frequency crystal (4) and a triple frequency crystal (5). By adjusting the front and rear positions of the focusing lens (3), the distance between the double frequency crystal (4) and the triple frequency crystal (5), and the temperature of the double frequency crystal (4) and the triple frequency crystal (5), the output ultraviolet light reaches the strongest; the infrared light output by the triple frequency crystal (5) is adjusted to a predetermined value. The external laser is shielded by an infrared light blocking block (6) after being transmitted in space, and the output green laser is shielded by a green light blocking block (7) after being transmitted in space. The imaging lens (8) is arranged on the propagation path of the output ultraviolet laser, and its imaging object surface corresponds to the Brewster angle output surface of the triple frequency crystal (5), and the image surface is located at the input surface of the wedge mirror (9). By slightly adjusting the spacing between the imaging lens (8) and the triple frequency crystal (5) and the spacing between the wedge mirror (9) and the imaging lens (8), the ultraviolet laser output by the wedge mirror (9) becomes circular and is output.

10. The extracavity frequency-doubled and pulse-width adjustable ultraviolet laser method according to claim 9, characterized in that: The infrared laser with adjustable pulse width is focused and its light intensity is enhanced to realize triple frequency output. The Brewster angle output surface of the triple frequency crystal (5) reduces the probability of ultraviolet damage and also separates infrared light, green light and ultraviolet light. The separated ultraviolet light is elliptical due to the walk-off effect and the wedge angle output. The wedge mirror (9) is shaped to ensure that the elliptical ratio of the elliptical spot input by the wedge mirror is approximately equal to the elliptical ratio of the light spot output by the triple frequency crystal. The imaging lens (8) between the triple frequency crystal (5) and the wedge mirror (9) performs an imaging operation to facilitate shaping. At the same time, the position of the imaging lens (8) is finely adjusted to compensate for the light spot ellipse caused by the walk-off effect during frequency doubling. While ensuring the output ultraviolet efficiency, damage is avoided and the ultraviolet output is shaped into a circular light spot.

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