Multi-cavity laser pulse compression device and femtosecond laser system using the same

Abstract

The utility model discloses a kind of multi-cavity laser pulse compression device and the application of femtosecond laser system, a kind of multi-cavity laser pulse compression device, comprising: at least one pair of optical reflection element, optical reflection element includes first reflector and second reflector, cavity between first reflector and second reflector, first reflector and second reflector are used to reflect the input laser pulse in cavity, to form the transmission path of multiple reflection;In cavity, lens structure is provided, lens structure is used to adjust the beam waist position, spatial mode and spectrum broadening condition of laser pulse in cavity, the combination piece formed by lens structure and optical reflection element is used to construct nonlinear broadening structure of non-converging type, multiple-path reflection.The utility model in optical reflection element in cavity, fully consider the spatial overlapping degree of beam propagation in cavity, the uniform utilization of first reflector and second reflector surface.

Description

Technical Field

[0001] This utility model relates to the fields of laser and nonlinear optics, and in particular to a multi-cavity laser pulse compression device and its application in a femtosecond laser system. Background Technology

[0002] With the rapid development of ultrafast laser technology, industry and scientific research have placed higher demands on femtosecond lasers with high power, high energy, and high repetition rates. While traditional Ti:sapphire femtosecond lasers possess extremely short pulse widths, they suffer from significant bottlenecks in average power, repetition rate, and overall system efficiency, making them unsuitable for high-load, high-stability industrial applications. In contrast, ytterbium-doped femtosecond laser systems (using the rare-earth element ytterbium (Yb) doped into matrix materials such as optical fibers or crystals) driven by gain media are becoming the mainstream choice for industrial ultrafast lasers due to their advantages such as high efficiency, high average power, and high repetition rate. However, the typical pulse width of these lasers is usually on the order of hundreds of femtoseconds, limiting the improvement of peak power and hindering efficiency enhancement in nonlinear optical processes. To further improve the peak power of these laser systems, time compression of the output pulse is necessary.

[0003] Conventional nonlinear pulse compression schemes, such as hollow fiber-filled rare gas devices, have been widely used in scientific research to achieve effective spectral broadening. However, due to the physical limitations of the hollow fiber structure, its damage threshold is far below the requirements of industrial high-power laser systems, making it difficult to withstand average power and high-energy pulses above 100 watts, resulting in significant power compatibility issues. Therefore, multi-cavity structures have been proposed as a more suitable nonlinear broadening scheme for high-power pulsed lasers.

[0004] Although the Herriott-type multi-cavity structure possesses the ability to realize multiple laser reflection paths and achieves effective broadening with low nonlinear accumulation, it still has some limitations. In the Herriott-type multi-cavity structure, the beam spot utilization efficiency is low because some areas of the mirror are not effectively utilized. Furthermore, in the standard Herriott configuration, severe overlap of repeated beam paths can easily exacerbate mirror damage. Additionally, the periodic focusing of the beam in the Herriott-type multi-cavity structure can easily induce strong nonlinear processes such as ionization and plasma formation in nonlinear media. The fixed optical path design of the Herriott-type multi-cavity structure makes it difficult to adapt to the needs of different power levels, different beam waist positions, and asymmetric optical path structures, which is detrimental to system miniaturization and modularization. Utility Model Content

[0005] This invention provides a multi-cavity laser pulse compression device and its application in a femtosecond laser system, which can solve the problems of insufficient mirror utilization, mirror damage, poor beam focusing and adaptation capabilities in the existing Herriott-type multi-cavity structure.

[0006] A multi-cavity laser pulse compression device includes: at least one pair of optical reflecting elements, wherein the optical reflecting elements include a first reflecting mirror and a second reflecting mirror, and a cavity is formed between the first reflecting mirror and the second reflecting mirror. The first reflecting mirror and the second reflecting mirror are used to reflect the input laser pulse within the cavity to form a transmission path with multiple reflections.

[0007] A lens structure is provided within the cavity. The lens structure is used to adjust the beam waist position, spatial mode, and spectral broadening conditions of the laser pulse within the cavity. The combination of the lens structure and the optical reflective element is used to construct a non-converging, multi-path reflection nonlinear broadening structure.

[0008] Preferably, the first reflector and the second reflector can be selected as concave mirrors, convex mirrors, cylindrical mirrors and plane mirrors.

[0009] Preferably, the first reflector and the second reflector are combined with different mirrors to form the optical reflective element with various configurations, including a double concave mirror configuration, a double cylindrical mirror configuration, a concave-convex mirror configuration, a double plane mirror configuration, and a planar-concave mirror configuration.

[0010] Preferably, the lens structure is a spherical lens or a cylindrical lens.

[0011] Preferably, a nonlinear medium is provided in the cavity to induce nonlinear effects during multiple reflections of the laser pulse.

[0012] Preferably, the distribution of the nonlinear medium includes: local filling in a preset widening region, discontinuous distribution in multiple regions, and uniform filling of the entire cavity.

[0013] Preferably, the nonlinear medium is a gas, liquid, or solid.

[0014] Preferably, the plurality of optical reflective elements are mounted on an external adjustable bracket.

[0015] Preferably, the spacing, angle, or number of light paths of the plurality of optical reflective elements are adjusted by mechanical, piezoelectric, or thermal means.

[0016] A femtosecond laser system uses a multi-cavity laser pulse compression device, comprising: a beam input coupling module and an output sampling module, wherein the beam input coupling module is used to guide the laser pulse into the cavity, and the output sampling module is used to extract the broadened pulse from the cavity for output.

[0017] The beneficial effects of this utility model are:

[0018] (1) In this utility model, a lens structure is set in the cavity of the optical reflective element, which fully considers the spatial overlap of the beam propagation in the cavity and the uniform utilization of the surfaces of the first and second reflective mirrors, thereby effectively suppressing local heat accumulation, improving the mirror utilization rate and reducing thermal damage.

[0019] (2) In this utility model, by combining optical reflection elements and lens structure, multi-segment reflection, optical path folding and asymmetric trajectory structure are introduced, which extends the effective propagation path within the limited physical space of the cavity, achieves a nonlinear accumulation length that is superior to that of traditional linear structures, significantly shortens the cavity size, and facilitates integration into industrial systems.

[0020] (3) In this utility model, the reflection path is constructed by combining a reflector and a lens, which further realizes non-focused transmission, effectively reduces the number of high-cost concave mirrors used, reduces the system construction cost, and enhances the optical path flexibility and scene adaptability of the device. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a mirror in a Herriott-type multi-cavity cavity at four times the focal length in the prior art.

[0022] Figure 2 This is a schematic diagram of the structure of a mirror in a Herriott-type multi-cavity cavity at twice the focal length in the prior art.

[0023] Figure 3 A schematic diagram of the dual cylindrical mirror configuration in a multi-cavity laser pulse compression device provided by this utility model;

[0024] Figure 4 This invention provides a structural schematic diagram of a concave-convex mirror configuration in a multi-cavity laser pulse compression device.

[0025] Figure 5 A schematic diagram of a dual-concave mirror matching plano-convex lens configuration in a multi-cavity laser pulse compression device provided by this utility model;

[0026] Figure 6 A schematic diagram of the plane mirror-concave mirror-plano-concave lens configuration in a multi-cavity laser pulse compression device provided by this utility model;

[0027] Figure 7 This invention provides a schematic diagram of the structure of a multi-cavity laser pulse compression device with dual plane mirrors matching various lens configurations.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1. First reflecting mirror; 2. Second reflecting mirror; 3. Lens structure. Detailed Implementation

[0030] The specific embodiments of this utility model are described in detail below, but it should be understood that the scope of protection of this utility model is not limited to the specific embodiments.

[0031] Several papers have documented multi-cavity pulse stretching systems based on Herriott-type mirror configurations, which successfully compressed ytterbium-doped laser pulses with an average power of 375W by approximately 10 times while maintaining a system efficiency of over 90%, demonstrating the feasibility and superiority of MPC in high-power laser pulse stretching. Therefore, Herriott-type multi-cavity structures are widely used in nonlinear pulse compression schemes.

[0032] Herriott-type multi-cavity structures typically consist of two or more mirrors, causing the light beam to undergo multiple reflections within the cavity. Each reflection alters the beam's path, allowing it to propagate within the cavity for an extended period.

[0033] The inventors discovered that although the Herriott-type multi-cavity structure has the ability to realize multiple laser reflection paths and can achieve effective broadening at low nonlinear accumulation, it still has some limitations. Herriott-type multi-cavity structures generally suffer from low spot utilization efficiency, severe overlap of beam repetition paths, periodic beam focusing, poor scalability, and limited adaptability.

[0034] Specifically, in the Herriott-type multi-cavity structure, the laser spot is only distributed in the outer edge region of the concave mirror, leaving most of the mirror surface unutilized, resulting in low space utilization and concentrated reflected heat at the edges, increasing the risk of localized thermal load on the mirror surface. Furthermore, in the standard Herriott configuration, multiple reflection points are periodically distributed, with some spots overlapping on the mirror surface, making heat dissipation difficult and further increasing the possibility of mirror damage. The fixed or repetitive beam focusing point within the cavity easily induces strong nonlinear processes (including but not limited to ionization and plasma formation) in the nonlinear medium, hindering further power increases. Due to the fixed optical path design, the Herriott-type multi-cavity structure is difficult to adapt to different power levels, different beam waist positions, and asymmetric optical path structures, which is detrimental to system miniaturization and modularization.

[0035] This utility model provides a multi-cavity laser pulse compression device, comprising: at least one pair of optical reflective elements, and multiple optical reflective elements mounted on an external adjustable bracket, wherein their spacing, angle or number of light paths is adjusted by mechanical, piezoelectric or thermodynamic means.

[0036] like Figures 1-2 As shown, the optical reflecting element is composed of two or more mirrors to form a multiple reflection path of the laser pulse within the cavity. In this embodiment, two mirrors are used, namely a first mirror 1 and a second mirror 2. The cavity between the first mirror 1 and the second mirror 2 is used to reflect the input laser pulse within the cavity to form a multiple reflection transmission path.

[0037] Specifically, a nonlinear medium is placed within the cavity to induce nonlinear effects during multiple reflections of the laser pulse. The nonlinear medium can be a gas, liquid, or solid. When the nonlinear medium is a gas, it includes inert gases and molecular gases, with components selected from helium, neon, argon, krypton, nitrogen, oxygen, air, or small organic molecule gases. When the nonlinear medium is a solid, a solid transparent material or combination of materials with good transmittance within the laser's operating wavelength range is used. The material is selected from quartz, sapphire, borosilicate glass, calcium fluoride (CaF2), and lithium fluoride (LiF), and its thickness can be set according to the required broadening. When the nonlinear medium is a liquid, its components are selected from deionized water, organic solvents, or other liquid materials with high transmittance and low absorption characteristics.

[0038] Furthermore, the nonlinear medium needs to be placed in the region of strongest nonlinear effect in the propagation path of the laser pulse within the cavity. This region can be located inside the cavity, near the optical reflective element, or at a position determined by adjusting the optical path layout. The distribution of the nonlinear medium includes, but is not limited to: locally filling a pre-defined broadening region, discontinuous distribution across multiple regions to achieve multi-level nonlinear effects, and uniform filling throughout the cavity to enhance nonlinear accumulation. The arrangement parameters of the nonlinear medium (such as position, length, pressure, or thickness) can be optimized according to laser parameters, nonlinear response intensity, or thermal management requirements to improve spectral broadening efficiency while suppressing unnecessary linear absorption, heat accumulation, and light intensity loss.

[0039] In this embodiment, the device is compatible with a variety of nonlinear media and can adjust the media type and distribution according to different application scenarios. It supports uniform filling of the entire cavity or layout of local action areas, thereby improving the expansion efficiency and reducing system losses.

[0040] like Figures 1-7As shown, the first reflecting mirror 1 and the second reflecting mirror 2 can be selected from concave mirrors, convex mirrors, cylindrical mirrors, and plane mirrors. The first reflecting mirror 1 and the second reflecting mirror 2 can form optical reflecting elements with various configurations by selecting different mirrors. The configurations include double concave mirror configuration (i.e., both the first reflecting mirror 1 and the second reflecting mirror 2 are concave mirrors), double cylindrical mirror configuration (i.e., both the first reflecting mirror 1 and the second reflecting mirror 2 are cylindrical mirrors and are concentrically nested), concave-convex mirror configuration (i.e., the first reflecting mirror 1 is a concave mirror and the second reflecting mirror 2 is a convex mirror), double plane mirror configuration (i.e., both the first reflecting mirror 1 and the second reflecting mirror 2 are plane mirrors), and plano-concave mirror configuration (i.e., the first reflecting mirror 1 is a concave mirror and the second reflecting mirror 2 is a plane mirror).

[0041] Among them, the double concave mirror configuration is used to construct Herriott-type orbits or confocal multi-pass orbits; the double cylindrical mirror configuration is used to achieve beam compression in the single-axis direction, reduce the degree of lateral focusing, avoid high-intensity induced ionization effects, adapt to high-energy laser systems, and improve space utilization and system stability; the concave-convex mirror configuration can keep the laser in an unfocused state in the cavity to suppress strong nonlinear effects such as ionization, be compatible with higher single-pulse energy and power output, and improve beam quality and space utilization efficiency; multiple sets of double plane mirror configuration arrays are used to construct compact reflection paths to realize multi-segment folding or asymmetric layout of the optical path; multiple sets of plano-concave mirror joint arrays are used to realize multi-segment folding, multi-track folding or asymmetric light transmission structure of the optical path, effectively reducing the overall size and improving layout flexibility.

[0042] A lens structure 3 is installed within the cavity. The lens structure 3 is used to adjust the beam waist position, spatial mode, and spectral broadening conditions of the laser pulse within the cavity. The lens structure 3 is a spherical lens or a cylindrical lens.

[0043] The spherical lens is used to adjust the focal length, optimize the spot diameter, and enhance the peak intensity to match the broadening response characteristics of the nonlinear medium. The cylindrical lens is used to focus the laser pulse only in one dimension to achieve anisotropic nonlinear broadening or spatial compression. Lens structure 3 can be positioned at the center of the cavity or in the middle of a Herriott-type track to change the equivalent optical path and focusing conditions in the multi-path. As an insert-type optical lens assembly, lens structure 3 has dispersion compensation capabilities. An anti-reflective coating is applied to the surface of lens structure 3 to improve transmission efficiency. The position of lens structure 3 is adjustable to accommodate different pulse widths and beam diameters. Lens structure 3 itself can be made of nonlinear materials, including but not limited to quartz, sapphire, borosilicate glass, calcium fluoride (CaF2), and lithium fluoride (LiF).

[0044] In existing technologies, such as Figures 1-2As shown, without lens structure 3, an optical reflecting element consisting of only two concave mirrors is used. The first mirror 1 and the second mirror 2 are configured in a 2F or 4F configuration, or they can be arranged asymmetrically according to spatial layout and beam propagation requirements. This structure is suitable for constructing traditional Herriot-type or improved multi-pass reflection paths.

[0045] Based on existing technology, those skilled in the art can explore the transmission of lasers in the optical field by changing the mirror types of the first reflecting mirror 1 and the second reflecting mirror 2 during the research and development process.

[0046] like Figure 3 As shown, the optical reflecting element adopts a double cylindrical mirror configuration, that is, the optical reflecting element is composed of two coaxially arranged cylindrical mirrors. The second reflecting mirror 2 is the inner cylindrical mirror, and the first reflecting mirror 1 is the outer reflecting mirror. The outer surface of the inner cylindrical mirror is coated with a reflective film, and the outer cylindrical mirror has a semi-enclosed structure, with its inner surface also coated with a reflective film. This ensures that both the inner surface of the first reflecting mirror 1 and the outer surface of the second reflecting mirror 2 have reflective capabilities, making it difficult for the light beam to pass through and facilitating multi-path reflection of the light beam within the cylindrical cavity of the ring. This configuration can achieve strong confinement of the laser in one dimension, thereby suppressing asymmetric focusing and improving the controllability of nonlinear effects.

[0047] like Figure 4 As shown, the assembly adopts a concave-convex mirror configuration, meaning the optical reflecting element uses a concave mirror and a convex mirror to form a reflecting pair. This combination can achieve weak focusing or quasi-parallel beam transmission, thereby effectively avoiding strong focusing regions within the cavity and improving the system's ability to handle high pulse energy.

[0048] like Figures 5-7 As shown, in the aforementioned multi-cavity basic structure, to further control the beam propagation characteristics, adjust the focusing position, and compensate for dispersion, the inventors introduced a lens structure 3 into the optical path. The assembly formed by the lens structure 3 and the optical reflecting element is used to construct a non-converging, multi-path reflection nonlinear broadening structure.

[0049] Specifically, such as Figure 5 As shown, the assembly adopts a double concave mirror matching plano-convex lens configuration. In this case, the optical reflecting element uses two concave mirrors, and the lens structure 3 uses a plano-convex lens. That is, a plano-convex lens is inserted between the first reflecting mirror 1 and the second reflecting mirror 2 to form a flexibly adjustable waist position in the cavity and further enhance the nonlinear response.

[0050] like Figure 6As shown, the assembly adopts a plane mirror-concave mirror-plano-concave lens configuration. In this case, the optical reflecting element uses one concave mirror and one plane mirror, and the lens structure 3 uses one plano-concave lens. That is, a plano-concave lens is inserted between the first reflecting mirror 1 and the second reflecting mirror 2 to expand the light spot size or achieve weak divergence propagation, which is suitable for application scenarios that reduce peak light intensity.

[0051] like Figure 7 As shown, the assembly uses a double-plane mirror to match various lens configurations. In this case, the optical reflecting element uses two plane mirrors to form a reflection path, and the lens structure 3 uses a plano-concave lens and a plano-convex lens. That is, a plano-concave lens, a plano-convex lens, and a plano-concave lens are sequentially inserted into the cavity between the first reflecting mirror 1 and the second reflecting mirror 2. This combination is used for composite control of beam divergence, dispersion compensation, and nonlinear accumulation path.

[0052] In its structural design, the device fully considers the spatial overlap of the beam propagation within the cavity and the uniform utilization of the surfaces of the first reflector 1 and the second reflector 2, effectively suppressing local heat accumulation, improving mirror utilization, reducing thermal damage, and enhancing the thermal stability and reflector lifespan of the system during long-term operation.

[0053] In this embodiment, by introducing multi-segment reflection, optical path reversal, and asymmetric trajectory structure, the effective propagation path is extended within the limited physical space of the cavity, achieving a nonlinear accumulation length superior to that of traditional linear structures, significantly shortening the cavity size, and facilitating integration into industrial systems.

[0054] Through flexible configurations of various optical structures, lens and medium combinations, this invention supports multi-channel switching, path adjustment, and modular component replacement, making it widely adaptable to industrial ultrafast lasers of the same wavelength, repetition rate, and pulse width. The multi-cavity laser pulse compression device provided by this invention achieves efficient nonlinear broadening of high-power, high-energy pulses while ensuring system stability and compactness, providing ideal input conditions for subsequent dispersion compensation and time compression. It is widely applicable to industrial-grade ultrafast laser processing, high-harmonic generation, and precision spectral measurement. Its high optical flexibility and structural integration provide a more efficient, stable, and compact nonlinear broadening and pulse compression solution for femtosecond lasers in material processing, high-harmonic generation, and spectral measurement scenarios.

[0055] This application proposes several innovative multi-pass cavity structures, expanding the range of optical configurations for traditional multi-pass cavities. Among them, optical reflecting elements employing concave-convex mirror configurations and double cylindrical mirror configurations can uniformly broaden the light beam within the cavity, avoiding regions with high peak light intensity. This effectively improves the system's ability to handle high single-pulse energy and high average power, effectively avoiding the strong focusing problem present in traditional Herriott-type cavities. While maintaining cavity compactness, this design significantly increases the upper limit of single-pulse energy and average power that the system can handle, further reducing the overall device size and improving the system's structural stability and thermal load capacity during long-term operation.

[0056] This application, by incorporating a lens structure 3—that is, introducing an inserted lens into the cavity of the optical reflective element—can adjust and broaden the originally strong focused spot in the Herriott-type cavity, thereby effectively suppressing strong nonlinear effects such as ionization and plasma formation, and improving the operational stability of the device under high-power lasers. Simultaneously, by constructing the reflection path through a combination of mirrors and lenses, non-focused transmission is further realized, effectively reducing the number of high-cost concave mirrors used, lowering system construction costs, and enhancing the device's optical path flexibility and adaptability to various scenarios, thus possessing broader potential for industrial and scientific research applications.

[0057] In one embodiment, the present invention provides a femtosecond laser system using a multi-cavity laser pulse compression device. The femtosecond laser system includes a beam input coupling module and an output sampling module. The beam input coupling module is used to guide the laser pulse into the cavity, and the output sampling module is used to extract the broadened pulse from the cavity for output.

[0058] Working principle: The pulsed laser emitted from the industrial laser first passes through the mode matching module and is reflected sequentially to adjust the spot size to the required size. Then, the beam input coupling module guides the laser pulse into the cavity of the multi-cavity laser pulse compression device, causing the beam to reflect multiple times between the first reflecting mirror 1 and the second reflecting mirror 2. During the reflection process, the lens structure 3 adjusts and broadens the strongly focused spot, effectively suppressing strong nonlinear effects such as ionization and plasma formation. Finally, the beam is reflected out of the cavity and output through the output sampling module.

[0059] The above-disclosed embodiments are only a few specific examples of the present utility model. However, the embodiments of the present utility model are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the protection scope of the present utility model.

Claims

1. A multi-cavity laser pulse compression device, characterized in that, include: At least one pair of optical reflective elements, the optical reflective elements including a first reflector (1) and a second reflector (2), the first reflector (1) and the second reflector (2) being a cavity, the first reflector (1) and the second reflector (2) being used to reflect the input laser pulse within the cavity to form a transmission path with multiple reflections; A lens structure (3) is provided in the cavity. The lens structure (3) is used to adjust the beam waist position, spatial mode and spectral broadening conditions of the laser pulse in the cavity. The combination formed by the lens structure (3) and the optical reflection element is used to construct a non-converging, multi-path reflection nonlinear broadening structure.

2. The multi-cavity laser pulse compression device as described in claim 1, characterized in that, The first reflector (1) and the second reflector (2) can be selected from concave mirrors, convex mirrors, cylindrical mirrors and plane mirrors.

3. The multi-cavity laser pulse compression device as described in claim 2, characterized in that, The first reflector (1) and the second reflector (2) form optical reflective elements with various configurations by selecting different mirrors. The configurations include double concave mirror configuration, double cylindrical mirror configuration, concave-convex mirror configuration, double plane mirror configuration, and planar-concave mirror configuration.

4. The multi-cavity laser pulse compression device as described in claim 1, characterized in that, The lens structure (3) adopts a spherical lens or a cylindrical lens.

5. The multi-cavity laser pulse compression device as described in claim 1, characterized in that, A nonlinear medium is provided in the cavity to induce nonlinear effects during multiple reflections of the laser pulse.

6. The multi-cavity laser pulse compression device as described in claim 5, characterized in that, The distribution forms of the nonlinear medium include: local filling in a preset widening area, discontinuous distribution in multiple areas, and uniform filling of the entire cavity.

7. The multi-cavity laser pulse compression device as described in claim 5, characterized in that, The nonlinear medium is a gas, liquid, or solid.

8. The multi-cavity laser pulse compression device as described in claim 1, characterized in that, Multiple optical reflective elements are mounted on an external adjustable bracket.

9. A multi-cavity laser pulse compression device as described in claim 8, characterized in that, The spacing, angle, or number of light paths of the plurality of optical reflective elements are adjusted by mechanical, piezoelectric, or thermodynamic means.

10. A femtosecond laser system using a multi-cavity laser pulse compression device as described in claims 1-9, characterized in that, include: The system includes a beam input coupling module and an output sampling module. The beam input coupling module is used to guide laser pulses into the cavity, and the output sampling module is used to extract the broadened pulses from the cavity for output.

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