A femtosecond laser frequency doubling device and method

Abstract

The application relates to the field of optical technology, and relates to a femtosecond laser frequency doubling device and method. The device comprises a femtosecond laser, a second-order frequency doubling crystal and a third-order frequency doubling crystal. A walk-off effect compensation component for compensating time walk-off effect and spatial walk-off effect is arranged between the femtosecond laser and the second-order frequency doubling crystal. The fundamental infrared light output by the femtosecond laser sequentially passes through the walk-off effect compensation component, the second-order frequency doubling crystal and the third-order frequency doubling crystal and is output. According to the application, the walk-off effect compensation component for compensating time walk-off effect and spatial walk-off effect is arranged between the femtosecond laser and the second-order frequency doubling crystal, the walk-off effect of the fundamental infrared light output by the femtosecond laser is compensated in time and space, the second-order frequency doubling crystal and the third-order frequency doubling crystal can efficiently double the frequency of the fundamental infrared light, and the third-order frequency doubling ultraviolet light with high beam quality is obtained.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and more specifically, to a femtosecond laser frequency doubling device and method. Background Technology

[0002] Ultrafast lasers in the ultraviolet band possess advantages such as short wavelength, small focused spot size, high single-photon energy, and high temporal resolution, and are widely used in fields such as ultrafast phenomena in physics and chemistry, biomedical microscopy, and ultra-fine micro / nano fabrication. Currently, most gain media used in laser research emit wavelengths primarily in the visible and infrared bands, especially ultrashort, ultra-intense pulsed lasers whose output wavelengths are mainly in the near-infrared band. Therefore, obtaining ultraviolet lasers by frequency doubling near-infrared lasers multiple times to reach the ultraviolet band has become a research focus.

[0003] A frequency-doubled laser is provided, comprising a first mirror, a second mirror, a gain medium, a telescope module, a polarization element, and a nonlinear crystal. The first mirror and the second mirror are spaced apart to form a resonant cavity for the frequency-doubled laser. The polarization element, the gain medium, the telescope module, and the nonlinear crystal are disposed in the resonant cavity, and the telescope module is disposed between the gain medium and the nonlinear crystal.

[0004] In the process of frequency doubling lasers, the nonlinear crystals can cause phenomena such as beam group velocity mismatch and beam space walk-off, which can lead to low frequency doubling efficiency and poor beam quality. Summary of the Invention

[0005] This invention provides a femtosecond laser frequency doubling device and method to overcome the shortcomings of low frequency doubling efficiency and poor beam quality of the existing technology.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention proposes a femtosecond laser frequency doubling device, comprising: a femtosecond laser, a second-harmonic crystal, and a third-harmonic crystal, wherein a walk-off effect compensation component for compensating for time walk-off effect and spatial walk-off effect is provided between the femtosecond laser and the second-harmonic crystal, and the fundamental frequency infrared light output by the femtosecond laser passes sequentially through the walk-off effect compensation component, the second-harmonic crystal, and the third-harmonic crystal before being output.

[0008] As a preferred technical solution, the walk-off effect compensation component includes a phase retarder for changing the polarization state direction of the fundamental frequency infrared light, and a group delay compensation piece for generating a crystal birefringence effect. The phase retarder is disposed between the femtosecond laser and the group delay compensation piece, and the group delay compensation piece is disposed between the phase retarder and the second harmonic crystal.

[0009] As a preferred technical solution, the group delay compensation sheet is a barium metaborate crystal.

[0010] As a preferred technical solution, the main optical surface of the group delay compensation chip is arranged perpendicularly to the main optical surface of the second harmonic crystal, and the main optical surface of the third harmonic crystal is arranged perpendicularly to the main optical surface of the second harmonic crystal.

[0011] As a preferred technical solution, a polarizing beam splitter is also provided between the second-harmonic crystal and the third-harmonic crystal.

[0012] As a preferred technical solution, a laser amplifier is also provided between the femtosecond laser and the walk-off effect compensation component.

[0013] As a preferred technical solution, the second harmonic crystal is a lithium triborate crystal, and the third harmonic crystal is a barium metaborate crystal.

[0014] Secondly, the present invention employs a femtosecond laser frequency doubling method using a femtosecond laser frequency doubling device as described in any of the technical solutions of the first aspect, comprising:

[0015] The fundamental frequency infrared light output by the femtosecond laser undergoes time and space walk-off compensation through a walk-off compensation component.

[0016] After time-walk-off compensation and space-walk-off compensation, the fundamental frequency infrared light is transmitted to the second harmonic crystal, where the second harmonic effect occurs, producing second harmonic green light.

[0017] The fundamental frequency infrared light and the second-harmonic green light are transmitted to the third-harmonic crystal for frequency combination, generating third-harmonic ultraviolet light.

[0018] As a preferred technical solution, the walk-off effect compensation component includes a phase retarder and a group retarder; the fundamental infrared light output from the femtosecond laser changes its polarization direction after passing through the phase retarder to obtain mutually perpendicular fundamental infrared o-light and fundamental infrared e-light; the fundamental infrared light with o-light and e-light perpendicular to each other generates a crystal birefringence effect after passing through the group retarder, thereby compensating for the time walk-off effect and spatial walk-off effect of the fundamental infrared light.

[0019] As a preferred technical solution, before the fundamental frequency infrared light and the second harmonic green light enter the third harmonic crystal for frequency combination, a polarizing beam splitter is used to guide the fundamental frequency infrared light out of the optical path.

[0020] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows: The present invention provides a walk-off effect compensation component between the femtosecond laser and the frequency-second crystal to compensate for the time walk-off effect and the spatial walk-off effect, thereby compensating for the fundamental frequency infrared light output by the femtosecond laser in terms of time and space. This enables the frequency-second and frequency-third crystals to efficiently double the fundamental frequency infrared light, resulting in high-quality frequency-third ultraviolet light. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the femtosecond laser frequency doubling device in the embodiments of this application.

[0022] Figure 2 This is a schematic diagram illustrating the principle of temporal and spatial walk-off of the walk-off effect compensation component in the embodiments of this application.

[0023] Figure 3 This is a schematic diagram illustrating the working principle of the femtosecond laser frequency doubling device in the embodiments of this application.

[0024] Figure 4 This is a flowchart of the femtosecond laser frequency doubling method in the embodiments of this application.

[0025] Among them, 1-femtosecond laser, 2-laser amplifier, 3-walk-off effect compensation component, 31-phase delay plate, 32-group delay compensation plate, 4-secondary frequency harmonic crystal, 5-polarizing beam splitter, 6-third frequency harmonic crystal. Detailed Implementation

[0026] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] Example 1

[0029] Please see Figure 1 This embodiment proposes a femtosecond laser frequency doubling device, including: a femtosecond laser 1, a second-harmonic crystal 4, and a third-harmonic crystal 6. A walk-off effect compensation component 3 for compensating for time walk-off effect and spatial walk-off effect is provided between the femtosecond laser 1 and the second-harmonic crystal 4. The fundamental frequency infrared light output by the femtosecond laser 1 passes through the walk-off effect compensation component 3, the second-harmonic crystal 4, and the third-harmonic crystal 6 in sequence before being output.

[0030] In the specific implementation process, the fundamental frequency infrared light output by the femtosecond laser 1 undergoes time and space walk-off compensation through the walk-off compensation component 3. The fundamental frequency infrared light, after time and space walk-off compensation, is transmitted to the second-harmonic crystal 4, where it undergoes a second-harmonic effect to generate second-harmonic green light. The fundamental frequency infrared light and the second-harmonic green light are then transmitted to the third-harmonic crystal 6 for frequency combination, generating third-harmonic ultraviolet light.

[0031] The femtosecond laser frequency doubling device proposed in this embodiment compensates for the temporal and spatial walk-off effects by setting a walk-off effect compensation component 3 between the femtosecond laser 1 and the second-harmonic crystal 4. This compensates for the temporal and spatial walk-off effects of the fundamental frequency infrared light output by the femtosecond laser 1, enabling the second-harmonic crystal 4 and the third-harmonic crystal 6 to efficiently double the fundamental frequency infrared light and obtain high-quality third-harmonic ultraviolet light.

[0032] Example 2

[0033] This embodiment is an improvement on the femtosecond laser frequency doubling device proposed in Embodiment 1.

[0034] In this embodiment, the femtosecond laser 1 outputs 1030nm fundamental frequency infrared light with an energy of 3mJ and a pulse width on the order of 300-500fs.

[0035] like Figure 2 As shown, Figure 2 The schematic diagram of the walk-off effect compensation component 3 for time and space walk-off is shown in this embodiment. The walk-off effect compensation component 3 includes a phase delay plate 31 for changing the polarization state direction of the fundamental frequency infrared light, and a group delay compensation plate 32 for generating crystal birefringence effect. The phase delay plate 31 is disposed between the femtosecond laser 1 and the group delay compensation plate 32, and the group delay compensation plate 32 is disposed between the phase delay plate 31 and the frequency-doubled crystal 4.

[0036] In this embodiment, the group delay compensation chip 32 is a barium metaborate crystal (BBO crystal).

[0037] In this embodiment, the second harmonic crystal 4 is a lithium triborate crystal (LBO crystal), and the third harmonic crystal 6 is a barium metaborate crystal (BBO crystal).

[0038] In this embodiment, the main optical surface of the group delay compensation chip 32 is arranged perpendicularly to the main optical surface of the second harmonic crystal 4.

[0039] In this embodiment, by adjusting the phase delay plate 31, the fundamental infrared o light incident on the second harmonic crystal 4 to generate second harmonic green light is 2.4 mJ, and the fundamental infrared e light incident on the third harmonic crystal 6 to generate third harmonic ultraviolet light through a sum-frequency interaction with the second harmonic green light is 0.6 mJ.

[0040] After passing through the group delay compensation plate 32, the fundamental infrared o-light is incident on the second-harmonic crystal 4, resulting in a second-harmonic effect and producing 515nm second-harmonic green light. To better achieve the subsequent third-harmonic process, beam quality is prioritized in this stage; therefore, an LBO crystal is selected as the second-harmonic crystal 4. The LBO crystal has a small spatial walk-off angle, dispersion, and group velocity walk-off between 1030nm and 515nm, achieving a doubling efficiency of up to 60%. The fundamental infrared o-light undergoes type I phase matching to produce 515nm second-harmonic e-light with 50% efficiency, thus obtaining 1.2mJ of 515nm second-harmonic green light. The lagging fundamental infrared e-light generated by the group delay compensation plate 32 is e-polarized for the second-harmonic crystal 4 and passes directly through it without participating in the second-harmonic effect. Therefore, it maintains its original excellent beam quality and temporal characteristics, which is highly beneficial for generating high-quality third-harmonic ultraviolet light during the frequency harmonic process with the second-harmonic green light. In addition, the fundamental frequency infrared e-light and the original leading fundamental frequency infrared o-light are separated at a certain angle, that is, they are not transmitted on the same optical axis, which is beneficial for separating the fundamental frequency infrared e-light and the frequency-doubled green light in the later stage.

[0041] In the walk-off compensation component 3, the fundamental infrared o-light with a relatively high group velocity serves as the pump light for the second-harmonic crystal 4. Through a type of phase matching (o+o-->e), second-harmonic green light is obtained. Simultaneously, both the second-harmonic green light and the fundamental infrared e-light used to generate third-harmonic ultraviolet light pass through the second-harmonic crystal 4. The two have almost no walk-off angle within the second-harmonic crystal 4, eliminating the need for separate compensation for their spatial walk-off. This simplifies the optical path design and further improves the beam quality and conversion efficiency of the third-harmonic ultraviolet light.

[0042] Since the 515nm second-harmonic green light generated in the second-harmonic crystal 4 through the second-harmonic effect is also an e-light, the second-harmonic green light and the fundamental infrared e-light, which are both e-lights, will produce the same walk-off angle as the fundamental infrared o-light when they are transmitted in the LBO crystal. However, the difference between the two walk-off angles is only 0.6mrad. Even after passing through the 3mm long second-harmonic crystal 4, their relative walk-off displacement is only 1.8 micrometers, which can be completely ignored. It can be considered that the two are almost collinearly transmitted, thus achieving the effect of spatial walk-off compensation.

[0043] like Figure 3The diagram illustrates the working principle of a femtosecond laser frequency doubling device. In practice, the fundamental infrared light output from the femtosecond laser 1 undergoes a change in polarization direction via the phase retardation plate 31, resulting in mutually perpendicular fundamental infrared o-beams and fundamental infrared e-beams. After passing through the phase retardation plate 31, the fundamental infrared light continues to be incident on the group delay compensation plate 32. At this point, the incident direction of the fundamental infrared light is 90° to the crystal optical axis of the group delay compensation plate 32. The group velocity difference between the fundamental infrared e-beams and fundamental infrared o-beams within the group delay compensation plate 32 is maximized, and there is no spatial walk-off effect. Furthermore, the group delay compensation plate 32 is a BBO crystal, with its principal optical surface perpendicularly positioned to the principal optical surface of the second harmonic crystal 4. This allows the leading e-beam within the group delay compensation plate 32 to be converted into o-beams and incident on the second harmonic crystal 4, compensating for the lag effect of the frequency-doubled light caused by the second harmonic effect of the fundamental infrared light in the second harmonic crystal 4. This achieves compensation for the time walk-off effect between the fundamental infrared light and the second harmonic green light during the subsequent third harmonic process.

[0044] In this embodiment, a polarizing beam splitter 5 is also provided between the second-harmonic crystal 4 and the third-harmonic crystal 6.

[0045] In the specific implementation process, after the 515nm second-harmonic green light is generated by the second-harmonic crystal 4, the remaining fundamental-frequency infrared (o-light) light from the frequency doubling process does not participate in the subsequent summation process with the second-harmonic green light. Instead, it is directly guided out of the optical path by the polarization beam splitter 5 (TFP). The 1030nm fundamental-frequency infrared (e-light) light and the 515nm second-harmonic green light after passing through the polarization beam splitter 5 are then incident on the third-harmonic crystal 6 for summation, generating 343nm third-harmonic ultraviolet light. Since this process needs to balance the beam quality and conversion efficiency after frequency doubling, a BBO crystal is selected as the third-harmonic crystal 6. The BBO crystal has a high nonlinear coefficient in the ultraviolet band, and its parameters such as dispersion, group velocity walk-off, and spatial walk-off angle are less different from those of the LBO crystal, resulting in higher overall conversion efficiency.

[0046] In this embodiment, the main optical surface of the third-harmonic crystal 6 and the main optical surface of the second-harmonic crystal 4 are arranged perpendicularly to each other, that is, they are consistent with the main optical surface of the group delay compensation chip 32.

[0047] In the specific implementation process, the main optical surface of the second harmonic crystal 4 and the main optical surface of the third harmonic crystal 6 are arranged perpendicularly to each other, so that the second harmonic green light and the fundamental infrared e-light passing through the second harmonic crystal 4 are transposed into o-light relative to the third harmonic crystal 6. In the third harmonic crystal 6, the 1.2mJ second harmonic green light and the 0.6mJ fundamental infrared light, both o-light, are phase matched by type I, and finally output 0.6mJ 343nm third harmonic ultraviolet light with a 33% efficiency through sum-frequency interaction. Because a group delay compensation plate 32 is pre-set, the second-harmonic green light leads the fundamental infrared e-light before third harmonic generation. However, since the fundamental infrared light travels faster than the second-harmonic green light in the third harmonic crystal 6, by reasonably designing the group delay compensation plate 32 to introduce a suitable group delay between the second-harmonic green light and the fundamental infrared e-light, the second-harmonic green light and the fundamental infrared e-light can achieve the highest degree of overlap in the third harmonic crystal 6, thereby realizing the generation of high-efficiency, high-beam-quality ultraviolet light pulses.

[0048] In this embodiment, a laser amplifier 2 is also provided between the femtosecond laser 1 and the walk-off effect compensation component 3.

[0049] In the specific implementation process, the femtosecond laser 1 outputs femtosecond light pulses, which are then passed through the laser amplifier 2 to output fundamental frequency infrared light with high average power, high single pulse energy, and femtosecond pulses.

[0050] The femtosecond laser frequency doubling device proposed in this embodiment compensates for the temporal and spatial walk-off effects by setting a walk-off effect compensation component 3 between the femtosecond laser 1 and the second-harmonic crystal 4. This compensates for the fundamental frequency infrared light output by the femtosecond laser 1 in both time and space, enabling the second-harmonic crystal 4 and the third-harmonic crystal 6 to efficiently double the fundamental frequency infrared light. This results in high-power, high-beam-quality, and high-power-stability third-harmonic ultraviolet light, forming a high-intensity, high-short laser pulse 2H (second-harmonic) and 3H (third-harmonic) frequency up-conversion module with precise temperature control, compact and reliable structure, simple maintenance, and strong adaptability to different application requirements. This device is then used for industrial demonstration.

[0051] The femtosecond laser frequency doubling device proposed in this embodiment can compensate for the temporal and spatial walk-off effects generated during the second and third harmonic processes in the entire system using only one group delay compensation plate 32. By designing a suitable group delay compensation plate 32, the group velocity walk-off of the nonlinear frequency doubling crystal for light pulses of different wavelengths can be effectively compensated, avoiding the complex optical path design of multiple second and third harmonic processes and the introduction of multiple sets of time and spatial walk-off compensation devices. This allows the beams participating in the second and third harmonic processes to have excellent beam quality and spatiotemporal overlap.

[0052] Example 3

[0053] See Figure 4 This embodiment proposes a femtosecond laser frequency doubling method for a femtosecond laser frequency doubling device, including:

[0054] The fundamental frequency infrared light output by the femtosecond laser 1 undergoes time walk-off compensation and spatial walk-off compensation through the walk-off compensation component 3.

[0055] In this embodiment, the femtosecond laser 1 outputs 1030nm fundamental frequency infrared light with an energy of 3mJ and a pulse width of 300-500fs.

[0056] In this embodiment, the walk-off effect compensation component 3 includes a phase retarder 31 and a group retarder 32. The fundamental infrared light output from the femtosecond laser 1 changes its polarization direction after passing through the phase retarder 31, resulting in mutually perpendicular fundamental infrared o-light and fundamental infrared e-light. The fundamental infrared light, which is perpendicular to the o-light and e-light, generates a crystal birefringence effect after passing through the group retarder 32, thereby compensating for the time walk-off effect and spatial walk-off effect of the fundamental infrared light.

[0057] In this embodiment, the group delay compensation chip 32 is a barium metaborate crystal (BBO crystal).

[0058] In this embodiment, the second harmonic crystal 4 is a lithium triborate crystal (LBO crystal), and the third harmonic crystal 6 is a barium metaborate crystal (BBO crystal).

[0059] After time-walk-off compensation and space-walk-off compensation, the fundamental frequency infrared light is transmitted to the second harmonic crystal 4, where the second harmonic effect occurs, producing second harmonic green light.

[0060] In this embodiment, the main optical surface of the group delay compensation chip 32 is arranged perpendicularly to the main optical surface of the second harmonic crystal 4.

[0061] In this embodiment, by adjusting the phase delay plate 31, the fundamental infrared o light incident on the second harmonic crystal 4 to generate second harmonic green light is 2.4 mJ, and the fundamental infrared e light incident on the third harmonic crystal 6 to generate third harmonic ultraviolet light through a sum-frequency interaction with the second harmonic green light is 0.6 mJ.

[0062] After passing through the group delay compensation plate 32, the fundamental infrared o-light is incident on the second-harmonic crystal 4, resulting in a second-harmonic effect and producing 515nm second-harmonic green light. To better achieve the subsequent third-harmonic process, beam quality is prioritized in this stage; therefore, an LBO crystal is selected as the second-harmonic crystal 4. The LBO crystal has a small spatial walk-off angle, dispersion, and group velocity walk-off between 1030nm and 515nm, achieving a doubling efficiency of up to 60%. After type-I phase matching, the fundamental infrared o-light produces a 515nm second-harmonic e-light with 50% efficiency, thus obtaining 1.2mJ of 515nm second-harmonic green light. The lagging pulse generated by the group delay compensation plate 32 is e-polarized for the second-harmonic crystal 4. It passes directly through the second-harmonic crystal 4 and walks off at a certain angle from the original leading fundamental infrared o-light, meaning they do not propagate on the same optical axis. This facilitates the subsequent separation of the fundamental infrared e-light and the second-harmonic green light.

[0063] Since the 515nm second-harmonic green light generated in the second-harmonic crystal 4 through the second-harmonic effect is also an e-light, the second-harmonic green light and the fundamental infrared e-light, which are both e-lights, will produce the same walk-off angle as the fundamental infrared o-light when they are transmitted in the LBO crystal. However, the difference between the two walk-off angles is only 0.6mrad. Even after passing through the 3mm long second-harmonic crystal 4, their relative walk-off displacement is only 1.8 micrometers, which can be completely ignored. It can be considered that the two are almost collinearly transmitted, thus achieving the effect of spatial walk-off compensation.

[0064] In the specific implementation process, the fundamental infrared light output by the femtosecond laser 1 undergoes a change in polarization direction after passing through the phase retardation plate 31, resulting in mutually perpendicular fundamental infrared o-light and fundamental infrared e-light. After passing through the phase retardation plate 31, the fundamental infrared light continues to be incident on the group delay compensation plate 32. At this time, the incident direction of the fundamental infrared light is 90° with the crystal optical axis of the group delay compensation plate 32. The group velocity difference between the fundamental infrared e-light and the fundamental infrared o-light in the group delay compensation plate 32 is maximized, and there is no space walk-off effect. In addition, the group delay compensation plate 32 is a BBO crystal, and its principal optical surface is set perpendicular to the principal optical surface of the second harmonic crystal 4. This allows the leading e-light in the group delay compensation plate 32 to be converted into o-light and incident on the second harmonic crystal 4, compensating for the lag effect of the second harmonic light caused by the second harmonic effect of the fundamental infrared light in the second harmonic crystal 4. This achieves compensation for the time walk-off effect between the fundamental infrared light and the second harmonic green light in the subsequent third harmonic process.

[0065] The fundamental frequency infrared light and the second-harmonic green light are transmitted to the third-harmonic crystal 6 for frequency combination, generating third-harmonic ultraviolet light.

[0066] In this embodiment, before the fundamental frequency infrared light and the second harmonic green light enter the third harmonic crystal 6 for frequency combination, the fundamental frequency infrared light is guided out of the optical path by the polarizing beam splitter 5.

[0067] In the specific implementation process, after the 515nm second-harmonic green light is generated by the second-harmonic crystal 4, the remaining fundamental-frequency infrared (o-light) light from the frequency doubling process does not participate in the subsequent summation process with the second-harmonic green light. Instead, it is directly guided out of the optical path by the polarization beam splitter 5 (TFP). The 1030nm fundamental-frequency infrared (e-light) light and the 515nm second-harmonic green light after passing through the polarization beam splitter 5 are then incident on the third-harmonic crystal 6 for summation, generating 343nm third-harmonic ultraviolet light. Since this process needs to balance the beam quality and conversion efficiency after frequency doubling, a BBO crystal is selected as the third-harmonic crystal 6. The BBO crystal has a high nonlinear coefficient in the ultraviolet band, and its parameters such as dispersion, group velocity walk-off, and spatial walk-off angle are less different from those of the LBO crystal, resulting in higher overall conversion efficiency.

[0068] In this embodiment, the main optical surface of the third-harmonic crystal 6 and the main optical surface of the second-harmonic crystal 4 are arranged perpendicularly to each other, that is, they are consistent with the main optical surface of the group delay compensation chip 32.

[0069] In the specific implementation process, the main optical surface of the second-harmonic crystal 4 and the main optical surface of the third-harmonic crystal 6 are arranged perpendicularly to each other, so that the second-harmonic green light and the fundamental infrared e-light, which are both e-light, passing through the second-harmonic crystal 4 are transposed into o-light relative to the third-harmonic crystal 6. In the third-harmonic crystal 6, the 1.2mJ second-harmonic green light and the 0.6mJ fundamental infrared e-light, which are both o-light, are phase matched of type I, and finally output 0.6mJ 343nm third-harmonic ultraviolet light with a 33% efficiency through sum-frequency interaction. Because a group delay compensation plate 32 is pre-set, the second-harmonic green light leads the fundamental infrared e-light before third harmonic generation. However, since the fundamental infrared e-light travels faster than the second-harmonic green light in the third harmonic crystal 6, by reasonably designing the group delay compensation plate 32 to introduce a suitable group delay between the second-harmonic green light and the fundamental infrared e-light, the second-harmonic green light and the fundamental infrared e-light can achieve the highest degree of overlap in the third harmonic crystal 6, thereby realizing the generation of high-efficiency, high-beam-quality ultraviolet light pulses.

[0070] The femtosecond laser frequency doubling method proposed in this embodiment compensates for the temporal and spatial walk-off effects by setting a walk-off effect compensation component 3 between the femtosecond laser 1 and the frequency-second crystal 4. This compensates for the temporal and spatial walk-off effects of the fundamental infrared light output by the femtosecond laser 1, enabling the frequency-second crystal 4 and the frequency-third crystal 6 to efficiently double the fundamental infrared light. This results in high-power, high-beam-quality, and high-power-stability third-harmonic ultraviolet light, forming a high-intensity, high-short laser pulse 2H second-harmonic and 3H third-harmonic frequency up-conversion module with precise temperature control, compact and reliable structure, simple maintenance, and strong adaptability to different application requirements. This module is then used for industrial demonstration.

[0071] The femtosecond laser frequency doubling method proposed in this embodiment can compensate for the temporal and spatial walk-off effects generated during the second and third harmonic processes in the entire system using only one group delay compensation plate 32. By designing a suitable group delay compensation plate 32, the group velocity walk-off of nonlinear frequency doubling crystals for light pulses of different wavelengths can be effectively compensated, avoiding the complex optical path design of multiple second and third harmonic processes and the introduction of multiple sets of temporal and spatial walk-off compensation devices. This allows the beams participating in the second and third harmonic processes to have excellent beam quality and spatiotemporal overlap.

[0072] The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0073] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A femtosecond laser frequency doubling device, characterized in that, include: A femtosecond laser (1), a second-harmonic crystal (4), and a third-harmonic crystal (6) are provided. A walk-off effect compensation component (3) for compensating for time walk-off effect and spatial walk-off effect is provided between the femtosecond laser (1) and the second-harmonic crystal (4). The femtosecond laser (1) outputs fundamental frequency infrared light through the walk-off effect compensation component (3), the second-harmonic crystal (4), and the third-harmonic crystal (6) in sequence before outputting. The walk-off effect compensation component (3) includes a phase delay plate (31) for changing the polarization state direction of the fundamental infrared light, and a group delay compensation plate (32) for generating crystal birefringence effect. The phase delay plate (31) is disposed between the femtosecond laser (1) and the group delay compensation plate (32), and the group delay compensation plate (32) is disposed between the phase delay plate (31) and the second harmonic crystal (4).

2. The femtosecond laser frequency doubling device according to claim 1, characterized in that, The group delay compensation chip (32) is a barium metaborate crystal.

3. The femtosecond laser frequency doubling device according to claim 1, characterized in that, The main optical surface of the group delay compensation chip (32) is arranged perpendicularly to the main optical surface of the second harmonic crystal (4), and the main optical surface of the third harmonic crystal (6) is arranged perpendicularly to the main optical surface of the second harmonic crystal (4).

4. The femtosecond laser frequency doubling device according to claim 1, characterized in that, A polarizing beam splitter (5) is also provided between the second-harmonic crystal (4) and the third-harmonic crystal (6).

5. The femtosecond laser frequency doubling device according to claim 1, characterized in that, A laser amplifier (2) is also provided between the femtosecond laser (1) and the walk-off effect compensation component (3).

6. The femtosecond laser frequency doubling device according to claim 1, characterized in that, The second harmonic crystal (4) is a lithium triborate crystal, and the third harmonic crystal (6) is a barium metaborate crystal.

7. A femtosecond laser frequency doubling method using the femtosecond laser frequency doubling device as described in any one of claims 1 to 6, characterized in that, include: The fundamental frequency infrared light output by the femtosecond laser (1) is compensated for both time and space walk-off effects by the walk-off effect compensation component (3); After time-walk-off compensation and space-walk-off compensation, the fundamental frequency infrared light is transmitted to the second harmonic crystal (4) to produce second harmonic effect and generate second harmonic green light; The fundamental infrared light and the second-harmonic green light are transmitted to the third-harmonic crystal (6) for frequency mixing to generate third-harmonic ultraviolet light.

8. The femtosecond laser frequency doubling method according to claim 7, characterized in that, The walk-off effect compensation component (3) includes a phase delay plate (31) and a group delay compensation plate (32). The fundamental infrared light output by the femtosecond laser (1) is polarized by the phase delay plate (31) to obtain fundamental infrared o-light and fundamental infrared e-light that are perpendicular to each other. The fundamental infrared o-light and fundamental infrared e-light, which are perpendicular to each other, generate a crystal birefringence effect after passing through the group delay compensation plate (32), thereby compensating for the time walk-off effect and the spatial walk-off effect of the fundamental infrared light.

9. The femtosecond laser frequency doubling method according to claim 8, characterized in that, Before the fundamental infrared light and the second-harmonic green light enter the third-harmonic crystal (6) for frequency combination, the fundamental infrared light is led out of the optical path by a polarizing beam splitter (5).

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