A femtosecond laser tripling device

Abstract

The utility model relates to a kind of femtosecond laser three frequency multiplication devices, the device includes femtosecond laser, frequency multiplication module, light splitting module, compensation module, polarization module and sum frequency module, femtosecond laser emits first frequency femtosecond laser, and frequency multiplication module is partly frequency multiplied as second frequency femtosecond laser. First frequency femtosecond laser not involved in frequency multiplication is transmitted to polarization module by light splitting module, and second frequency femtosecond laser obtained by frequency multiplication is reflected to compensation module. Polarization module adjusts the polarization direction of first frequency femtosecond laser, so that it is consistent with the polarization state of second frequency femtosecond laser after being processed by compensation module, and is projected to sum frequency module. Compensation module carries out optical path difference compensation to second frequency femtosecond laser, to ensure that it is time synchronization when first frequency femtosecond laser and second frequency femtosecond laser propagate to sum frequency module. Sum frequency module is frequency multiplied as third frequency femtosecond laser and is outputted to two kinds of femtosecond laser, and the third frequency conversion of femtosecond laser is realized.

Description

Technical Field

[0001] This application relates to the field of femtosecond laser technology, and in particular to a femtosecond laser frequency tripler device. Background Technology

[0002] With the continuous development of ultrafast photonics and deep ultraviolet applications, traditional light sources are no longer sufficient to meet the demands of high-energy excited-state detection and precision machining. Femtosecond laser frequency-triple harmonic technology, as a key technology for generating deep ultraviolet lasers, is becoming increasingly important.

[0003] However, existing femtosecond laser frequency-triple harmonic technology has many problems. In terms of optical path design, some schemes use a loop optical path to multiplex unconverted light, which increases the number of system components, makes the optical path more complex, and reduces system stability, making it susceptible to vibration and cascading failures. Other schemes use non-collinear phase matching to simplify the optical path, but this causes group velocity mismatch, resulting in pulse time-domain drift, which in turn reduces sum-frequency efficiency and causes beam distortion.

[0004] Existing technologies for optical path compensation have significant shortcomings. Some solutions use dispersive glass compensation plates for optical path compensation, but connecting multiple compensation plates in series increases the device size and makes it sensitive to vibration. Other solutions use special crystals, such as BBSAG crystals, to improve stability, but their low nonlinear coefficients result in a significant decrease in laser conversion efficiency.

[0005] Furthermore, existing high-performance femtosecond laser frequency-third harmonic systems are generally complex in structure, difficult to assemble and adjust, and extremely sensitive to environmental disturbances. These problems seriously hinder the practical application and industrialization of this technology. Therefore, developing a femtosecond laser frequency-third harmonic device with a simple optical path, precise optical path compensation, high conversion efficiency, and strong stability is of significant practical importance. Utility Model Content

[0006] Based on this, the purpose of this utility model is to provide a femtosecond laser frequency tripler device that achieves a simple optical path, accurate optical path compensation, high conversion efficiency and strong stability of femtosecond laser frequency tripler.

[0007] The femtosecond laser frequency third harmonic device described in this application includes a femtosecond laser (101), a frequency doubling module (102), a beam splitting module (103), a compensation module (104), a polarization module (105), and a sum-frequency module (106).

[0008] The femtosecond laser (101) is used to emit a femtosecond laser at a first frequency;

[0009] The frequency doubling module (102) is arranged on the propagation path of the first frequency femtosecond laser. The frequency doubling module (102) is used to multiply a portion of the first frequency femtosecond laser to a second frequency femtosecond laser, and output the second frequency femtosecond laser and the remaining portion of the first frequency femtosecond laser that has not participated in the frequency doubling.

[0010] The beam splitting module (103) is arranged on the output optical path of the frequency doubling module (102) and is used to transmit the first frequency femtosecond laser beam that has not participated in the frequency doubling to the polarization module (105) and to reflect the second frequency femtosecond laser beam to the compensation module (104).

[0011] The polarization module (105) is arranged on the transmission optical path of the first frequency femtosecond laser and is used to adjust the polarization direction of the first frequency femtosecond laser so that the polarization state of the first frequency femtosecond laser and the second frequency femtosecond laser processed by the compensation module (104) are consistent, and the adjusted first frequency femtosecond laser is projected onto the sum-frequency module (106).

[0012] The compensation module (104) is arranged on the reflected light path of the second frequency femtosecond laser and is used to compensate for the optical path difference of the second frequency femtosecond laser. The compensated second frequency femtosecond laser is then projected onto the sum-frequency module (106) so that the second frequency femtosecond laser and the first frequency femtosecond laser are synchronized in time when they propagate to the sum-frequency module (106).

[0013] The frequency summing module (106) is arranged on the output optical path of the polarization module (105) and the compensation module (104) to sum the first frequency femtosecond laser and the second frequency femtosecond laser into a three-times frequency femtosecond laser and output it.

[0014] In the femtosecond laser frequency tripler device of this invention, the first frequency femtosecond laser output by the femtosecond laser (101) enters the frequency doubling module (102). Based on its own structural characteristics, the frequency doubling module (102) multiplies part of the first frequency femtosecond laser to a second frequency femtosecond laser, outputting the second frequency femtosecond laser and the remaining first frequency femtosecond laser that did not participate in the frequency doubling, thus realizing the initial frequency conversion of the laser. The beam splitting module (103), based on a specific optical structure, performs beam splitting processing on the two laser frequencies, accurately transmitting the first frequency femtosecond laser beam to the polarization module (105), and reflecting the second frequency femtosecond laser beam to the compensation module (104). The polarization module (105) adjusts the polarization direction of the first frequency femtosecond laser to make it consistent with the polarization state of the second frequency femtosecond laser after processing by the compensation module (104). This structural design effectively solves the problem of low sum-frequency efficiency caused by the difference in polarization state, providing a foundation for subsequent high-efficiency sum-frequency conversion. The compensation module (104) is used to accurately compensate for the optical path difference of the second-frequency femtosecond laser, ensuring that the second-frequency femtosecond laser and the first-frequency femtosecond laser maintain strict time synchronization when they propagate to the summing module (106). This design overcomes the defects in the prior art, such as pulse time-domain walk-off caused by optical path differences, and significantly improves the summing efficiency. Finally, the summing module (106) efficiently sums the first-frequency femtosecond laser and the second-frequency femtosecond laser into a three-times-frequency femtosecond laser and outputs it.

[0015] The overall device has a compact structure, and the rational layout of the modules avoids the problems of increased component quantity and poor system stability caused by complex optical path designs. Furthermore, assembly and adjustment are relatively simple. At the same time, the device is insensitive to environmental disturbances and exhibits good stability while ensuring high conversion efficiency. It provides reliable structural support for the practical application of femtosecond laser frequency-triple harmonic technology, promoting its practical application and industrialization in related fields.

[0016] To better understand and implement this application, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a femtosecond laser frequency tripler device according to an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings. Wherein, when the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0019] It should be understood that the embodiments described below do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0020] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application are also intended to include the plural forms unless the context clearly indicates otherwise. Furthermore, in the description of this application, unless otherwise stated, “a plurality” means two or more. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items, for example, A and / or B, which can represent: A alone, A and B together, and B alone; the character “ / ” generally indicates that the preceding and following objects are in an “or” relationship.

[0021] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, this information should not be limited to these terms, and these terms are only used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. Depending on the context, the word "if" as used in this application can be interpreted as "when," "when," or "in response to determination."

[0022] With the continuous development of ultrafast photonics and deep ultraviolet applications, traditional light sources are no longer sufficient to meet the demands of high-energy excited-state detection and precision machining. Femtosecond laser frequency-triple harmonic technology, as a key technology for generating deep ultraviolet lasers, is becoming increasingly important.

[0023] However, existing femtosecond laser frequency-triple harmonic technology has many problems. In terms of optical path design, some schemes use a loop optical path to multiplex unconverted light, which increases the number of system components, makes the optical path more complex, and reduces system stability, making it susceptible to vibration and cascading failures. Other schemes use non-collinear phase matching to simplify the optical path, but this causes group velocity mismatch, resulting in pulse time-domain drift, which in turn reduces sum-frequency efficiency and causes beam distortion.

[0024] Existing technologies for optical path compensation have significant shortcomings. Some solutions use dispersive glass compensation plates for optical path compensation, but connecting multiple compensation plates in series increases the device size and makes it sensitive to vibration. Other solutions use special crystals, such as BBSAG crystals, to improve stability, but their low nonlinear coefficients result in a significant decrease in laser conversion efficiency.

[0025] Furthermore, existing high-performance femtosecond laser frequency-third harmonic systems are generally complex in structure, difficult to assemble and adjust, and extremely sensitive to environmental disturbances. These problems seriously hinder the practical application and industrialization of this technology. Therefore, developing a femtosecond laser frequency-third harmonic device with a simple optical path, precise optical path compensation, high conversion efficiency, and strong stability is of significant practical importance.

[0026] Please refer to Figure 1 The femtosecond laser frequency triplet device described in this application includes a femtosecond laser (101), a frequency doubling module (102), a beam splitting module (103), a compensation module (104), a polarization module (105), and a sum-frequency module (106).

[0027] The femtosecond laser (101) is used to emit a femtosecond laser at a first frequency;

[0028] The frequency doubling module (102) is arranged on the propagation path of the first frequency femtosecond laser. The frequency doubling module (102) is used to multiply a portion of the first frequency femtosecond laser to a second frequency femtosecond laser, and output the second frequency femtosecond laser and the remaining portion of the first frequency femtosecond laser that has not participated in the frequency doubling.

[0029] The beam splitting module (103) is arranged on the output optical path of the frequency doubling module (102) and is used to transmit the first frequency femtosecond laser beam that has not participated in the frequency doubling to the polarization module (105) and to reflect the second frequency femtosecond laser beam to the compensation module (104).

[0030] The polarization module (105) is arranged on the transmission optical path of the first frequency femtosecond laser and is used to adjust the polarization direction of the first frequency femtosecond laser so that the polarization state of the first frequency femtosecond laser and the second frequency femtosecond laser processed by the compensation module (104) are consistent, and the adjusted first frequency femtosecond laser is projected onto the sum-frequency module (106).

[0031] The compensation module (104) is arranged on the reflected optical path of the second frequency femtosecond laser and is used to compensate for the optical path difference of the second frequency femtosecond laser and project the second frequency femtosecond laser after optical path difference compensation onto the sum frequency module (106).

[0032] The frequency summing module (106) is arranged on the output optical path of the polarization module (105) and the compensation module (104) to sum the first frequency femtosecond laser and the second frequency femtosecond laser into a three-times frequency femtosecond laser and output it.

[0033] Among them, the femtosecond laser (101) is a device capable of emitting femtosecond-level pulsed lasers. Femtosecond lasers have the characteristics of extremely short pulse width, extremely high peak power and wide spectral range. In this invention, it is the source for generating the first frequency femtosecond laser, providing the basic laser energy for subsequent frequency doubling, sum-frequency and other processes.

[0034] The frequency doubling module (102) is designed based on the principle of nonlinear optics. Nonlinear optics refers to the nonlinear relationship between the response of a medium to light and the light intensity when the light intensity reaches a certain level. The frequency doubling module utilizes this characteristic to convert part of the energy of the input first-frequency femtosecond laser into a second-frequency femtosecond laser, thereby doubling the frequency, while outputting the remaining first-frequency femtosecond laser that did not participate in the frequency doubling.

[0035] The beam splitting module (103) is designed based on the differences in the propagation characteristics of lasers of different frequencies in optical media. When lasers of different frequencies pass through certain optical elements, the ratio of reflection to transmission will be different. The beam splitting module utilizes this characteristic to split and transmit the first-frequency femtosecond laser that has not participated in frequency doubling, and to split and reflect the second-frequency femtosecond laser, thereby realizing the separate transmission of lasers of different frequencies.

[0036] The main function of the compensation module (104) is to compensate for the optical path difference of the second-frequency femtosecond laser. The optical path refers to the product of the geometric path of light propagating in a medium and the refractive index of the medium. Due to the influence of different paths or different optical components, the second-frequency femtosecond laser may produce an optical path difference, causing it to be out of sync with the first-frequency femtosecond laser in time. The compensation module (104) eliminates this optical path difference through reasonable design, ensuring that the two remain in sync when they propagate to the sum-frequency module.

[0037] The polarization module (105) is used to adjust the polarization direction of the laser. The polarization of the laser refers to the vibration direction of the electric field vector of the light wave. The polarization module changes the polarization direction of the first frequency femtosecond laser through specific optical structures, such as waveplates and polarizers, so that it is consistent with the polarization state of the second frequency femtosecond laser after being processed by the compensation module. This is crucial for the subsequent sum-frequency process, because consistent polarization state can improve the sum-frequency efficiency.

[0038] The frequency-sum module (106) is also based on the principle of nonlinear optics. It can interact two lasers of different frequencies (a first-frequency femtosecond laser and a second-frequency femtosecond laser) to generate a femtosecond laser with a frequency three times the sum of the two frequencies, and realize the output of the laser.

[0039] In the femtosecond laser frequency tripler device of this invention, the first frequency femtosecond laser output by the femtosecond laser (101) enters the frequency doubling module (102). Based on its own structural characteristics, the frequency doubling module (102) multiplies part of the first frequency femtosecond laser to a second frequency femtosecond laser, outputting the second frequency femtosecond laser and the remaining first frequency femtosecond laser that did not participate in the frequency doubling, thus realizing the initial frequency conversion of the laser. The beam splitting module (103), based on a specific optical structure, performs beam splitting processing on the two laser frequencies, accurately transmitting the first frequency femtosecond laser beam to the polarization module (105), and reflecting the second frequency femtosecond laser beam to the compensation module (104). The polarization module (105) adjusts the polarization direction of the first frequency femtosecond laser to make it consistent with the polarization state of the second frequency femtosecond laser after processing by the compensation module (104). This structural design effectively solves the problem of low sum-frequency efficiency caused by the difference in polarization state, providing a foundation for subsequent high-efficiency sum-frequency conversion. The compensation module (104) is used to accurately compensate for the optical path difference of the second-frequency femtosecond laser, ensuring that the second-frequency femtosecond laser and the first-frequency femtosecond laser maintain strict time synchronization when they propagate to the summing module (106). This design overcomes the defects in the prior art, such as pulse time-domain walk-off caused by optical path differences, and significantly improves the summing efficiency. Finally, the summing module (106) efficiently sums the first-frequency femtosecond laser and the second-frequency femtosecond laser into a three-times-frequency femtosecond laser and outputs it.

[0040] The overall device has a compact structure, and the rational layout of the modules avoids the problems of increased component quantity and poor system stability caused by complex optical path designs. Furthermore, assembly and adjustment are relatively simple. At the same time, the device is insensitive to environmental disturbances and exhibits good stability while ensuring high conversion efficiency. It provides reliable structural support for the practical application of femtosecond laser frequency-triple harmonic technology, promoting its practical application and industrialization in related fields.

[0041] In one embodiment, the frequency doubling module (102) includes an aperture (SH1), a beam collimation module (B2), and a first nonlinear crystal (BBO1);

[0042] The aperture (SH1) is arranged in the output optical path of the femtosecond laser (101) and is used to perform spatial filtering and beam constraint on the first frequency femtosecond laser emitted by the femtosecond laser (101).

[0043] The beam collimation module (B2) is arranged on the output optical path of the aperture (SH1) and is used to collimate the first frequency femtosecond laser after spatial filtering and beam constraint.

[0044] The first nonlinear crystal (BBO1) is arranged in the output optical path of the beam collimation module (B2) to frequency double the first frequency femtosecond laser after beam collimation to a second frequency femtosecond laser.

[0045] The aperture stop (SH1) is an optical element whose main function is to perform spatial filtering and beam confinement on the light beam. Spatial filtering can remove stray light and higher-order mode components from the light beam, thereby improving the beam quality; beam confinement can control the diameter and divergence angle of the light beam, allowing the light beam to propagate in a more regular shape, providing good beam conditions for subsequent optical processing.

[0046] The beam-shrinking and collimation module (B2) is mainly used for beam shrinking and collimation of the first-frequency femtosecond laser after aperture processing. Beam shrinking refers to reducing the diameter of the beam, which is achieved through a specific combination of optical lenses, thus helping to improve the power density of the beam. Collimation, on the other hand, makes the beam propagation direction more parallel, reduces beam divergence, and ensures that the beam maintains good collimation during propagation, so that the subsequent frequency doubling effect can be more effective in the nonlinear crystal.

[0047] The first nonlinear crystal (BBO1) is a commonly used nonlinear optical crystal. Under strong light fields, the polarization intensity of a nonlinear crystal exhibits a nonlinear relationship with the incident light field strength. In this embodiment, the first nonlinear crystal is a BBO1 crystal. Utilizing this nonlinear optical property, the BBO1 crystal can partially convert the input, collimated, first-frequency femtosecond laser into a second-frequency femtosecond laser through nonlinear optical processes such as sum-frequency conversion, achieving frequency multiplication.

[0048] In this embodiment, the frequency doubling module (102) consists of an aperture (SH1), a beam collimation module (B2), and a first nonlinear crystal (BBO1). These components work together sequentially to partially double the frequency of the first-frequency femtosecond laser beam to the second-frequency femtosecond laser beam. When the femtosecond laser (101) emits the first-frequency femtosecond laser beam, the aperture (SH1) is first positioned on the output optical path of the femtosecond laser beam to perform spatial filtering, removing stray light and other undesirable components from the beam. Simultaneously, the beam is constrained, controlling its shape to ensure it continues to propagate in a cleaner and more regular state. Next, the beam collimation module (B2) is located on the output optical path of the aperture (SH1) to perform beam collimation on the first-frequency femtosecond laser beam after the aperture processing, reducing the beam diameter and increasing the beam power density. Simultaneously, it performs collimation processing, making the beam propagation direction more parallel and reducing divergence, thus creating favorable conditions for the subsequent frequency doubling process in the nonlinear crystal. Finally, the first-frequency femtosecond laser, after beam collimation, enters the first nonlinear crystal (BBO1). Due to the nonlinear optical properties of the first nonlinear crystal (BBO1), a portion of the first-frequency femtosecond laser undergoes nonlinear interaction within the crystal, resulting in frequency doubling to the second-frequency femtosecond laser. Simultaneously, the remaining portion of the first-frequency femtosecond laser that did not participate in frequency doubling is output together with the second-frequency femtosecond laser, completing the function of the frequency doubling module (102). The entire frequency doubling module, through the orderly cooperation of its components, achieves effective frequency doubling of the first-frequency femtosecond laser.

[0049] In one embodiment, the beam-shrinking collimation module (B2) includes a beam-shrinking lens (L1) and a concave lens (L2);

[0050] The beam-shrinking lens (L1) is arranged on the light output path of the aperture (SH1) and is used to shrink the first frequency femtosecond laser after spatial filtering and beam constraint.

[0051] The concave lens (L2) is arranged in the light output path of the beam-contracting lens (L1) to collimate the first frequency femtosecond laser beam that has passed through the beam-contracting lens into a parallel beam.

[0052] The beam-shrinking lens (L1) is an optical lens whose main function is to change the diameter of a laser beam. Through a specific curvature design and optical principles, when a first-frequency femtosecond laser passes through the beam-shrinking lens, the beam is refracted under the lens's influence, thus reducing the beam diameter. Beam shrinking can increase the power density of the beam, concentrating more light energy in a smaller area, which is crucial for achieving efficient frequency doubling in nonlinear crystals.

[0053] A concave lens (L2) is a lens that is thinner in the middle and thicker at the edges, and it has a diverging effect on light. In this embodiment, the main function of the concave lens is to collimate the first-frequency femtosecond laser beam after it has been beam-contracted. The beam after beam contraction may have some divergence. Through its special shape and optical properties, the concave lens can adjust the divergent beam into a parallel beam, ensuring that the beam maintains good collimation during propagation and reducing beam diffusion and energy loss.

[0054] In this embodiment, the beam-shrinking collimation module (B2) consists of a beam-shrinking lens (L1) and a concave lens (L2). When the first-frequency femtosecond laser beam exits from the aperture (SH1), it first reaches the beam-shrinking lens (L1). The beam-shrinking lens (L1), utilizing its optical properties, refracts the beam, reducing its diameter and increasing its power density, thus providing higher-energy beam conditions for the subsequent frequency doubling process in the nonlinear crystal. Subsequently, the first-frequency femtosecond laser beam, after beam shrinking, enters the concave lens (L2). Since the beam may diverge after beam shrinking, the concave lens (L2) uses the characteristics of its diverging rays to collimate the beam. It adjusts the diverging beam into a parallel beam, ensuring that the beam maintains a stable propagation direction and a small divergence angle during subsequent propagation, allowing it to enter the first nonlinear crystal (BBO1) in a favorable state for frequency doubling. The entire beam-shrinking and collimating module (B2) achieves the beam-shrinking and collimating function of the first frequency femtosecond laser through the orderly cooperation of the beam-shrinking lens (L1) and the concave lens (L2), laying the foundation for the efficient frequency doubling effect in the frequency doubling module (102).

[0055] In one embodiment, the beam splitting module (103) is a dichroic mirror (BS1), which is arranged at a 45° angle to the propagation direction of the first frequency femtosecond laser to realize the transmission of the first frequency femtosecond laser and the reflection of the second frequency femtosecond laser, and the propagation directions of the transmitted and reflected beams are perpendicular to each other.

[0056] The dichroscope (BS1) is a special optical element that exhibits different reflection and transmission characteristics for light of different wavelengths (frequency). In this invention, the BS1 allows the first-frequency femtosecond laser to pass through while simultaneously reflecting the second-frequency femtosecond laser, based on the frequency difference between the first and second-frequency femtosecond lasers. Furthermore, through careful design, the propagation directions of the transmitted and reflected beams are made perpendicular to each other, thereby achieving effective separation of lasers of different frequencies.

[0057] In this embodiment, the beam splitting module (103) uses a dichroic mirror (BS1) and is positioned at a 45° angle to the propagation direction of the first-frequency femtosecond laser. When the beam processed by the frequency doubling module (102) reaches the dichroic mirror (BS1), due to the difference in characteristics of the dichroic mirror for different frequencies of light, the first-frequency femtosecond laser will be transmitted through the dichroic mirror, while the second-frequency femtosecond laser will be reflected by the dichroic mirror. Because the dichroic mirror is positioned at a 45° angle to the propagation direction of the first-frequency femtosecond laser, the propagation directions of the transmitted first-frequency femtosecond laser and the reflected second-frequency femtosecond laser are perpendicular to each other. This design effectively separates the first-frequency femtosecond laser that has not participated in frequency doubling from the second-frequency femtosecond laser that has already been frequency-doubled, guiding them to different subsequent modules for further processing. This provides a clear and orderly optical path foundation for the subsequent polarization adjustment, optical path compensation, and sum-frequency operation of the entire femtosecond laser frequency doubling device, ensuring that the device can operate efficiently and stably.

[0058] In one embodiment, the compensation module (104) includes a second reflector (M2) and a fifth reflector (M5) arranged sequentially on the reflection path of the dichroic mirror (BS1), and a third reflector (M3) and a fourth reflector (M4) arranged sequentially along the propagation direction of the reflection path.

[0059] The second reflector (M2) reflects the second frequency femtosecond laser reflected by the dichroic mirror (BS1) to the third reflector (M3); the third reflector (M3) reflects the second frequency femtosecond laser to the fourth reflector (M4); the fourth reflector (M4) reflects the second frequency femtosecond laser to the fifth reflector (M5); the fifth reflector (M5) reflects the second frequency femtosecond laser to the sum-frequency module (106);

[0060] The compensation module (104) is used to compensate for the optical path difference of the second frequency femtosecond laser by adjusting the distances of the first reflector (M2) and the fifth reflector (M5) relative to the third reflector (M3) and the fourth reflector (M4), respectively.

[0061] In this embodiment, the compensation module (104) includes a second reflecting mirror (M2) and a fifth reflecting mirror (M5) sequentially arranged on the reflection path of the dichroic mirror (BS1), and a third reflecting mirror (M3) and a fourth reflecting mirror (M4) sequentially arranged along the propagation direction of the reflected light path. The principle of this compensation module to achieve optical path difference compensation is to adjust the distances of the second reflecting mirror (M2) and the fifth reflecting mirror (M5) relative to the third reflecting mirror (M3) and the fourth reflecting mirror (M4), respectively. Since the optical path is related to the geometric path of light propagation, changing the distance between the reflecting mirrors changes the optical path of the second-frequency femtosecond laser. By precisely adjusting these distances, the optical path difference that may exist in the second-frequency femtosecond laser can be eliminated, so that it maintains strict time synchronization with the first-frequency femtosecond laser when it propagates to the frequency-triple-frequency module (106), thereby improving the frequency-triple-frequency efficiency of the subsequent frequency-triple-frequency module and ensuring the efficient and stable operation of the entire femtosecond laser frequency-triple-frequency device.

[0062] In one embodiment, the compensation module (104) further includes a translation stage, on which the third reflector (M3) and the fourth reflector (M4) are arranged;

[0063] The translation stage is used to adjust the distances of the third reflector (M3) and the fourth reflector (M4) relative to the second reflector (M2) and the fifth reflector (M5), respectively.

[0064] A translation stage is a mechanical device capable of achieving precise linear displacement, typically composed of guide rails, sliders, and a drive mechanism. It can move according to a set direction and distance, ensuring high accuracy. In this compensation module, the translation stage provides an adjustable mounting platform for the third reflector (M3) and the fourth reflector (M4), allowing the positions of the reflectors to be changed by moving the stage.

[0065] In this embodiment, the compensation module (104) is further enhanced with a translation stage, on which the third reflector (M3) and the fourth reflector (M4) are positioned. The translation stage functions when optical path difference compensation for the second-frequency femtosecond laser is required. By controlling the movement of the translation stage, the positions of the third reflector (M3) and the fourth reflector (M4) can be precisely adjusted, thereby changing their distances relative to the second reflector (M2) and the fifth reflector (M5), respectively. Since the optical path is the product of the geometric path of light propagating in a medium and the refractive index of the medium, changing the geometric path can adjust the optical path when the refractive index of the medium remains constant. In this way, the potential optical path difference of the second-frequency femtosecond laser can be eliminated, ensuring that it remains time-synchronized with the first-frequency femtosecond laser when it propagates to the frequency-sum module (106). This effectively improves the frequency-sum efficiency of the frequency-sum module and ensures the stable operation and good performance of the entire femtosecond laser third-frequency harmonic device.

[0066] In one embodiment, the polarization module (105) includes a sixth reflector (M6), a half-wave plate (P1), and a seventh reflector (M7);

[0067] The sixth reflecting mirror (M6) is arranged in the transmission light path of the dichroic mirror (BS1) and is used to reflect the first frequency femtosecond laser to the half-wave plate (P1).

[0068] The half-wave plate (P1) is arranged in the light output path of the sixth reflecting mirror (M6) and is used to adjust the polarization direction of the first frequency femtosecond laser.

[0069] The seventh reflector (M7) is arranged in the light output path of the half-wave plate (P1) and is used to reflect the polarization-adjusted first frequency femtosecond laser to the sum-frequency module (106).

[0070] The half-wave plate (P1) is an optical element made of a birefringent material. When linearly polarized light is incident on the half-wave plate, the plate rotates the vibration direction of the linearly polarized light relative to the vibration direction of the incident light by a certain angle (usually twice the angle between the optical axis of the half-wave plate and the polarization direction of the incident light). In this embodiment, the half-wave plate (P1) is used to adjust the polarization direction of the first frequency femtosecond laser to match the polarization state of the second frequency femtosecond laser after processing by the compensation module.

[0071] In this embodiment, the polarization module (105) consists of a sixth reflecting mirror (M6), a half-wave plate (P1), and a seventh reflecting mirror (M7). These components work together sequentially to adjust the polarization direction of the first-frequency femtosecond laser. When the first-frequency femtosecond laser is transmitted from the dichroic mirror (BS1), it first reaches the sixth reflecting mirror (M6). The sixth reflecting mirror (M6) reflects the first-frequency femtosecond laser to the half-wave plate (P1), changing the beam's propagation direction and allowing it to enter the half-wave plate for polarization adjustment. The half-wave plate (P1) is located in the light path of the sixth reflecting mirror (M6). After the first-frequency femtosecond laser enters the half-wave plate, the half-wave plate utilizes its birefringence to adjust the polarization direction of the first-frequency femtosecond laser, changing its polarization state to prepare for its subsequent alignment with the polarization state of the second-frequency femtosecond laser. Finally, the polarization-adjusted first-frequency femtosecond laser reaches the seventh reflecting mirror (M7). The seventh reflector (M7) reflects the polarization-adjusted first-frequency femtosecond laser to the frequency summing module (106), ensuring that the first-frequency femtosecond laser can smoothly enter the frequency summing module. It then efficiently sums with the second-frequency femtosecond laser, which has been processed by the compensation module, in the frequency summing module, thus achieving the third harmonic output of the femtosecond laser. Through the orderly cooperation of its components, the entire polarization module effectively adjusts the polarization direction of the first-frequency femtosecond laser.

[0072] In one embodiment, the sum-frequency module (106) includes a beam splitter (BS2), a focusing lens (L3), a second nonlinear crystal (BBO2), and a plano-convex lens (L4);

[0073] The beam splitter (BS2) includes a first surface and a second surface; the first surface faces the output optical path of the polarization module (105), and the second surface faces the output optical path of the compensation module (104). The first frequency femtosecond laser is reflected by the first surface and the second frequency femtosecond laser is transmitted by the second surface to obtain the first frequency femtosecond laser and the second frequency femtosecond laser after merging.

[0074] The focusing lens (L3) is arranged in the output optical path of the beam splitter (BS2) and is used to focus the first frequency femtosecond laser and the second frequency femtosecond laser after they are combined.

[0075] The second nonlinear crystal (BBO2) is arranged in the light output path of the focusing lens (L3) and is located at the non-focal point of the focusing lens (L3), and is used to combine the focused first frequency femtosecond laser with the second frequency femtosecond laser to a frequency three times that of the femtosecond laser.

[0076] The plano-convex lens (L4) is arranged in the light output path of the second nonlinear crystal (BBO2) to collimate the sum-frequency tripled femtosecond laser into a parallel beam for output.

[0077] The beam splitter (BS2) is an optical element capable of reflecting and transmitting incident light in a specific ratio. In this embodiment, the beam splitter (BS2) has two surfaces, which can perform different optical operations on the incident first-frequency femtosecond laser and the second-frequency femtosecond laser, respectively, so that the two laser beams can be merged, creating conditions for subsequent frequency merging.

[0078] The focusing lens (L3) is a lens that converges parallel light beams to a single point. It utilizes the principle of light refraction to change the propagation direction of an incident parallel beam, causing it to converge at the focal point. In this frequency-switching module, the focusing lens (L3) is used to focus the combined first-frequency femtosecond laser beam and the second-frequency femtosecond laser beam, thereby increasing the energy density of the beam.

[0079] The second nonlinear crystal (BBO2) is a commonly used nonlinear optical crystal. Under the influence of a strong laser, the polarization intensity of a nonlinear crystal exhibits a nonlinear relationship with the incident light field intensity, thus enabling nonlinear optical effects such as frequency conversion. In this module, the second nonlinear crystal (BBO2) is used to combine a focused first-frequency femtosecond laser with a second-frequency femtosecond laser at a frequency three times greater.

[0080] A plano-convex lens (L4) is a lens with one flat surface and the other convex surface. It functions to collimate a light beam, that is, to adjust a diverging or converging beam into a parallel beam. In this embodiment, the plano-convex lens (L4) is used to collimate the summed frequency three-fold femtosecond laser into a parallel beam for subsequent use and processing.

[0081] In the sum-frequency module (106) of this embodiment, the beam splitter (BS2) plays a crucial role. Its first surface faces the output optical path of the polarization module (105). When the first-frequency femtosecond laser arrives, the first surface of the beam splitter (BS2) reflects the laser. Simultaneously, the second surface of the beam splitter (BS2) faces the output optical path of the compensation module (104). When the second-frequency femtosecond laser arrives, the second surface transmits the laser. In this way, the beam splitter (BS2) achieves the merging of the first-frequency and second-frequency femtosecond lasers. Next, the merged first-frequency and second-frequency femtosecond lasers enter the input optical path of the focusing lens (L3). The focusing lens (L3) uses the principle of light refraction to focus these two laser beams, making their beam energy more concentrated in space, increasing the energy density, and creating favorable conditions for subsequent efficient sum-frequency generation in the nonlinear crystal. Then, the focused laser beam reaches the second nonlinear crystal (BBO2). The second nonlinear crystal (BBO2) is located at the nonfocal point of the focusing lens (L3). Under the influence of a powerful laser, the nonlinear effect inside the crystal is excited, and the first-frequency femtosecond laser and the second-frequency femtosecond laser undergo a frequency-suppression interaction within the crystal to generate a third-frequency femtosecond laser. Finally, the frequency-suppressed third-frequency femtosecond laser exits from the second nonlinear crystal (BBO2) and enters the incident light path of the plano-convex lens (L4). The plano-convex lens (L4) collimates this laser beam, adjusting it into a parallel beam before its exit, resulting in a final output third-frequency femtosecond laser with good directionality and parallelism, facilitating subsequent laser applications and further processing. The entire frequency-suppression module efficiently completes the third-frequency harmonic generation process of the femtosecond laser through the coordinated work of its components.

[0082] In one embodiment, the first frequency femtosecond laser is an 800nm ​​femtosecond laser, the second frequency femtosecond laser is a 400nm femtosecond laser, and the triple frequency femtosecond laser is a 266nm femtosecond laser.

[0083] The focal length of the narrowing lens (L1) is 150mm, and the focal length of the concave lens (L2) is -50mm.

[0084] The first nonlinear crystal (BBO1) is a BBO crystal with a matching angle of 26.7°;

[0085] The displacement adjustment range of the translation stage is 0-50mm, and the adjustment accuracy is not less than 0.01mm;

[0086] The second nonlinear crystal (BBO2) is a BBO crystal with a matching angle of 44.2°;

[0087] The focusing lens (L3) is a convex lens with a focal length of 100mm.

[0088] The beam-shrinking system consists of a beam-shrinking lens (L1) and a concave lens (L2). Based on lens imaging formulas and the design principles of optical systems, combinations of lenses with different focal lengths can achieve beam-shrinking operations. The combination of a convex lens (beam-shrinking lens L1) with a focal length of 150mm and a concave lens (L2) with a focal length of -50mm can alter the beam diameter and divergence angle of the 800nm ​​femtosecond laser, thus meeting the requirements of subsequent optical components (such as the first nonlinear crystal BBO1) for the incident beam and improving the interaction efficiency of the beam within the nonlinear crystal.

[0089] The first nonlinear crystal uses a BBO crystal, which possesses excellent nonlinear optical properties and a wide transmission range. Class-one matching refers to the situation where, during frequency conversion in a nonlinear crystal, the polarization directions of the interacting light waves are the same. The matching angle of 26.7° was determined through precise calculation and experimentation. At this angle, an 800nm ​​femtosecond laser can efficiently undergo nonlinear effects in the BBO1 crystal, achieving specific frequency conversions (such as frequency doubling), preparing for the subsequent generation of a 400nm laser. Similar to the first nonlinear crystal, the second nonlinear crystal (BBO2) also uses a BBO crystal and is classified as class-one matching. The matching angle of 44.2° was determined for the sum-frequency operation of 800nm ​​and 400nm femtosecond lasers in the BBO2 crystal. At this angle, the two laser beams can efficiently undergo a sum-frequency effect, generating a 266nm femtosecond laser at three times the frequency.

[0090] The translation stage is used to adjust the positions of the third reflector (M3) and the fourth reflector (M4), thereby changing the optical path of the 400nm femtosecond laser. The 0-50mm adjustment range provides sufficient optical path adjustment space to compensate for potential path differences between the 400nm and 800nm ​​lasers during propagation. An adjustment accuracy of no less than 0.01mm ensures precise optical path adjustment, enabling accurate time synchronization of the two laser beams in the sum-frequency module and improving sum-frequency efficiency.

[0091] The function of the focusing lens (L3) is to focus the combined 800nm ​​and 400nm femtosecond laser beams, thereby increasing the energy density of the beam. The convex lens with a focal length of 100mm can focus the beam to a suitable size, so that the beam has sufficient energy density in the second nonlinear crystal (BBO2), thereby exciting nonlinear effects and achieving efficient sum-frequency conversion.

[0092] In this embodiment, the first frequency femtosecond laser is an 800nm ​​femtosecond laser, the second frequency femtosecond laser is a 400nm femtosecond laser, and the final generated triple-frequency femtosecond laser is a 266nm femtosecond laser. That is, the 800nm ​​femtosecond laser is the initial input laser, and the 400nm femtosecond laser is obtained after frequency doubling and used to perform a frequency-sum operation with the 800nm ​​laser in the frequency-sum module, ultimately producing a 266nm triple-frequency femtosecond laser. Different wavelengths of laser have different propagation characteristics and application scenarios in optical systems; the 266nm ultraviolet laser has important applications in microfabrication, biomedicine, and other fields.

[0093] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of this application, and this application also intends to include these modifications and variations.

Claims

1. A femtosecond laser frequency third-harmonic device, characterized in that, It includes a femtosecond laser (101), a frequency doubling module (102), a beam splitting module (103), a compensation module (104), a polarization module (105), and a sum-frequency module (106). The femtosecond laser (101) is used to emit a femtosecond laser at a first frequency; The frequency doubling module (102) is arranged on the propagation path of the first frequency femtosecond laser. The frequency doubling module (102) is used to multiply a portion of the first frequency femtosecond laser to a second frequency femtosecond laser, and output the second frequency femtosecond laser and the remaining portion of the first frequency femtosecond laser that has not participated in the frequency doubling. The beam splitting module (103) is arranged on the output optical path of the frequency doubling module (102) and is used to transmit the first frequency femtosecond laser beam that has not participated in the frequency doubling to the polarization module (105) and to reflect the second frequency femtosecond laser beam to the compensation module (104). The polarization module (105) is arranged on the transmission optical path of the first frequency femtosecond laser and is used to adjust the polarization direction of the first frequency femtosecond laser so that the polarization state of the first frequency femtosecond laser and the second frequency femtosecond laser processed by the compensation module (104) are consistent, and the adjusted first frequency femtosecond laser is projected onto the sum frequency module (106). The compensation module (104) is arranged on the reflected light path of the second frequency femtosecond laser and is used to compensate for the optical path difference of the second frequency femtosecond laser and project the second frequency femtosecond laser after optical path difference compensation onto the sum frequency module (106). The frequency summing module (106) is arranged on the output optical path of the polarization module (105) and the compensation module (104) to sum the first frequency femtosecond laser and the second frequency femtosecond laser into a three-times frequency femtosecond laser and output it.

2. The femtosecond laser frequency third harmonic device according to claim 1, characterized in that, The frequency doubling module (102) includes an aperture (SH1), a beam collimation module (B2), and a first nonlinear crystal (BBO1). The aperture (SH1) is arranged in the output optical path of the femtosecond laser (101) and is used to perform spatial filtering and beam confinement on the first frequency femtosecond laser emitted by the femtosecond laser (101). The beam collimation module (B2) is arranged on the output optical path of the aperture (SH1) and is used to collimate the first frequency femtosecond laser after spatial filtering and beam constraint. The first nonlinear crystal (BBO1) is arranged in the output optical path of the beam collimation module (B2) and is used to frequency double the first frequency femtosecond laser after beam collimation to a second frequency femtosecond laser.

3. The femtosecond laser frequency third harmonic device according to claim 2, characterized in that, The beam-contraction collimation module (B2) includes a beam-contraction lens (L1) and a concave lens (L2). The beam-shrinking lens (L1) is arranged on the light output path of the aperture (SH1) and is used to shrink the first frequency femtosecond laser after spatial filtering and beam constraint. The concave lens (L2) is arranged in the light output path of the beam-contracting lens (L1) to collimate the first frequency femtosecond laser beam that has passed through the beam-contracting lens into a parallel beam.

4. The femtosecond laser frequency third harmonic device according to claim 3, characterized in that, The beam splitting module (103) is a dichroic mirror (BS1). The dichroic mirror (BS1) is arranged at a 45° angle to the propagation direction of the first frequency femtosecond laser, and is used to realize the transmission of the first frequency femtosecond laser and the reflection of the second frequency femtosecond laser. The propagation directions of the transmitted and reflected beams are perpendicular to each other.

5. The femtosecond laser frequency third harmonic device according to claim 4, characterized in that, The compensation module (104) includes a second reflector (M2) and a fifth reflector (M5) arranged sequentially on the reflection path of the dichroic mirror (BS1), and a third reflector (M3) and a fourth reflector (M4) arranged sequentially along the propagation direction of the reflection path. The second reflector (M2) reflects the second frequency femtosecond laser reflected by the dichroic mirror (BS1) to the third reflector (M3); the third reflector (M3) reflects the second frequency femtosecond laser to the fourth reflector (M4); the fourth reflector (M4) reflects the second frequency femtosecond laser to the fifth reflector (M5); and the fifth reflector (M5) reflects the second frequency femtosecond laser to the sum-frequency module (106). The compensation module (104) is used to compensate for the optical path difference of the second frequency femtosecond laser by adjusting the distances of the second reflector (M2) and the fifth reflector (M5) relative to the third reflector (M3) and the fourth reflector (M4), respectively.

6. The femtosecond laser frequency third harmonic device according to claim 5, characterized in that, The compensation module (104) also includes a translation stage, on which the third reflector (M3) and the fourth reflector (M4) are arranged; The translation stage is used to adjust the distances of the third reflector (M3) and the fourth reflector (M4) relative to the second reflector (M2) and the fifth reflector (M5), respectively.

7. The femtosecond laser frequency third harmonic device according to claim 6, characterized in that, The polarization module (105) includes a sixth reflector (M6), a half-wave plate (P1), and a seventh reflector (M7). The sixth reflecting mirror (M6) is arranged in the transmission light path of the dichroic mirror (BS1) and is used to reflect the first frequency femtosecond laser to the half-wave plate (P1). The half-wave plate (P1) is arranged in the light output path of the sixth reflecting mirror (M6) and is used to adjust the polarization direction of the first frequency femtosecond laser. The seventh reflector (M7) is arranged on the light output path of the half-wave plate (P1) and is used to reflect the polarization-adjusted first frequency femtosecond laser to the sum-frequency module (106).

8. The femtosecond laser frequency third harmonic device according to claim 7, characterized in that, The sum-frequency module (106) includes a beam splitter (BS2), a focusing lens (L3), a second nonlinear crystal (BBO2), and a plano-convex lens (L4). The beam splitter (BS2) includes a first surface and a second surface; the first surface faces the output optical path of the polarization module (105), and the second surface faces the output optical path of the compensation module (104). The first frequency femtosecond laser is reflected by the first surface and the second frequency femtosecond laser is transmitted by the second surface to obtain the first frequency femtosecond laser and the second frequency femtosecond laser after merging. The focusing lens (L3) is arranged in the output light path of the beam splitter (BS2) and is used to focus the first frequency femtosecond laser and the second frequency femtosecond laser after they are combined. The second nonlinear crystal (BBO2) is arranged in the light output path of the focusing lens (L3) and is located at the non-focal point of the focusing lens (L3), and is used to combine the focused first frequency femtosecond laser with the second frequency femtosecond laser to a frequency three times that of the femtosecond laser. The plano-convex lens (L4) is arranged in the light output path of the second nonlinear crystal (BBO2) to collimate the sum-frequency triple-frequency femtosecond laser into a parallel beam for output.

9. The femtosecond laser frequency third harmonic device according to claim 8, characterized in that, The first frequency femtosecond laser is an 800nm ​​femtosecond laser, the second frequency femtosecond laser is a 400nm femtosecond laser, and the triple frequency femtosecond laser is a 266nm femtosecond laser; The focal length of the constricting lens (L1) is 150mm, and the focal length of the concave lens (L2) is -50mm. The first nonlinear crystal (BBO1) is a BBO crystal with a matching angle of 26.7°; The displacement adjustment range of the translation stage is 0-50mm, and the adjustment accuracy is not less than 0.01mm; The second nonlinear crystal (BBO2) is a BBO crystal with a matching angle of 44.2°; The focusing lens (L3) is a convex lens with a focal length of 100mm.

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