High power broadband tunable long-wave mid-infrared femtosecond laser generation device and method

Abstract

This invention discloses a high-power, broadband, tunable long-wavelength mid-infrared femtosecond laser generation device and method. The laser beam is split into a first beam and a second beam. The first beam pumps a first YAG crystal to generate a first supercontinuum, from which a signal light of a predetermined wavelength is selected. The signal light undergoes at least two cascaded optical parametric amplification stages to generate a high-power mid-infrared pump light. The second beam pumps a second YAG crystal to generate a second supercontinuum covering the long-wavelength infrared band as a seed light. This seed light is then incident on a BGGSe crystal for optical parametric amplification. Using a 1.5μm high-power femtosecond laser as the pump source, combined with the BGGSe nonlinear crystal for optical parametric amplification, the wide transmission range and high nonlinear coefficient of the BGGSe crystal are effectively utilized. Phase matching in the 6–18μm band can be achieved under 1.5μm pumping conditions, thereby obtaining a broadband, high-power, femtosecond-level laser output covering the long-wavelength mid-infrared band.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and specifically to a high-power broadband tunable long-wavelength mid-infrared femtosecond laser generation device and method. Background Technology

[0002] Long-wavelength mid-infrared (approximately 10–16 μm) light sources have significant applications in molecular fingerprinting, selective photolysis of biological tissues, strong-field physics, and environmental monitoring. This band covers the absorption peaks of many molecular fundamental vibrations, thus requiring femtosecond laser sources with broadband, high peak power, and stable output capabilities. However, the generation of broadband high-power femtosecond pulses in this band remains a significant challenge due to limitations in the transparency window, damage threshold, dispersion characteristics, and phase-matching conditions of available nonlinear crystals.

[0003] Existing technologies often employ second-order nonlinear frequency conversion methods based on difference frequency generation (DFG), optical parametric amplification (OPA), or optical parametric oscillation (OPO). Commonly used nonlinear crystals include ZnGeP2 (ZGP), AgGaS2 (AGS), AgGaSe2 (AGSe), GaSe, and BaGa4Se7 (BGSe). These materials each have limitations in terms of operating wavelength, nonlinear coefficient, bandwidth, damage threshold, and machinability. For example, while ZGP has a high nonlinear coefficient, its transparent region is limited to approximately 10 μm, and due to the crystal bandgap, it requires a light source with a diameter greater than 2 μm for pumping. AGS and AGSe crystals exhibit good transmittance near 10 μm, but they have lower nonlinear coefficients, weak birefringence, and significant group velocity mismatch. Although GaSe has a wide transmission band and high nonlinearity, its layered crystal structure results in low mechanical strength, making it difficult to process, and it imposes strict limitations on incident polarization, which is detrimental to stable operation under high average power pumping conditions. Although BGSe crystal (d11=24.3pm / V) can cover a transmission range of 18μm, its nonlinear coefficient is smaller than that of BaGa2GeSe6 (BGGSe, d11=66pm / V), resulting in lower efficiency. Furthermore, BGSe crystal has a monoclinic structure, making it more sensitive to processing, orientation, angle control, and stress control, and its lower heat dissipation coefficient makes it prone to thermal damage in high-power applications. In contrast, BGGSe is a tricrystalline crystal, easier to process, cut, polish, and orient, and has good chemical stability, requiring no complex post-annealing treatment.

[0004] BGGSe crystals possess wide transmission range, high nonlinearity, low dispersion, and high damage threshold, making them excellent materials for generating high-power, long-wavelength mid-infrared femtosecond lasers. However, most existing BGGSe-based mid-infrared femtosecond laser devices have limited spectral coverage and still fall short in terms of high power. Specifically, in existing BGGSe-based OPA technology: (1) Due to limitations in crystal phase-matching design and group velocity mismatch, the gain for long wavelengths remains limited, making it difficult to obtain 10–16 μm femtosecond pulses and resulting in a small wavelength tuning range; (2) Some devices generate 10–16 μm outputs through intra-pulse difference frequency generation, but due to limitations in pump source power, the output power is only 20 mW, and its energy is highly dispersed throughout the entire spectral domain, leading to a significant reduction in the spectral power density of a single band. Summary of the Invention

[0005] The purpose of this invention is to address the problems of narrow long-wavelength tuning range, low power, and compact structure in existing BGGSe-based optical parametric amplification technology when generating 10–16 μm long-wavelength mid-infrared femtosecond pulses. The invention provides a long-wavelength mid-infrared femtosecond optical parametric amplification device and method based on BGGSe crystal that can achieve wide tuning range, high power, and stable output.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for generating high-power broadband tunable long-wavelength mid-infrared femtosecond laser includes the following steps:

[0008] A femtosecond pump laser is provided and split into a first beam and a second beam;

[0009] The first beam is used to pump the first YAG crystal to generate a first supercontinuum, and a signal light of a predetermined wavelength is selected from it.

[0010] The signal light is subjected to at least two cascaded optical parametric amplification stages to generate high-power mid-infrared pump light;

[0011] The second beam is used to pump the second YAG crystal to generate a second supercontinuum covering the long-wave infrared band as a seed light.

[0012] After spatially combining and temporally synchronizing the high-power mid-infrared pump light with the seed light, they are jointly incident on a BGGSe crystal for optical parametric amplification.

[0013] By adjusting the phase matching angle of the BGGSe crystal, continuous tuning of the output wavelength can be achieved, resulting in high-power, broadband tunable long-wavelength mid-infrared femtosecond laser output.

[0014] This invention aims to construct a long-wavelength mid-infrared femtosecond light source capable of achieving wide tuning range, high power, and long-term stable output within the 10–16 μm range. It addresses the problem of low gain in BGGSe crystals at long wavelengths (10–16 μm), which makes it difficult to obtain broadband tunable long-wavelength mid-infrared femtosecond pulses.

[0015] As a preferred embodiment, the femtosecond pump laser has a center wavelength of 1 μm, an average power of 100 W, a repetition frequency of 500 kHz, and a pulse width of 300 fs.

[0016] The beam splitting into a first beam and a second beam is achieved through a beam splitting unit consisting of a half-wave plate HWP1 and a thin-film polarizer TFP1.

[0017] As a preferred embodiment, the steps of generating the first supercontinuum and selecting the signal light include: focusing the first beam sequentially through an aperture Iris1 and a lens B1 into the first YAG crystal to generate a supercontinuum; after the supercontinuum is collimated by a lens C1, the residual pump light is filtered out by a long-pass filter LPF1, and then focused by a lens C2 with a focal length of 150mm to obtain a signal light with a center wavelength of 1.5μm.

[0018] As a preferred embodiment, the at least two cascaded optical parametric amplification stages specifically refer to:

[0019] The 1.5μm signal light and the 1μm pump light, which is controlled by the second beam through the half-wave plate HWP2, the thin-film polarizer TFP2, the high-reflection mirror HR1, the delay device Delay1 and the lens B2, are combined in the KTP1 crystal through the dichroic mirror DM1 for the first stage of amplification, and the output power is 200mW of 1.5μm laser.

[0020] The 1.5μm laser beam amplified in the first stage is filtered by a dichroic mirror DM2 and a long-pass filter LPF2 to remove residual pump light. Then, it passes through a 150mm focal length C3 lens and a dichroic mirror DM3. Together with the 1μm pump light generated by the second beam through a half-wave plate HWP3, a thin-film polarizer TFP3, a high-reflection mirror HR2, a delay device Delay2, and a lens B3, the beam is combined in a KTP2 crystal for the second stage amplification, producing a high-power 1.5μm pump light with an average power of 10W.

[0021] As a preferred embodiment, the step of generating the seed light includes: focusing the second beam sequentially through an aperture Iris2 and a lens B4 into the second YAG crystal to generate a second supercontinuum; the second supercontinuum is collimated by a lens C5 and filtered by a long-pass filter LPF4 to remove residual pump light, and then used as the seed light.

[0022] As a preferred method, the spatial beam combining is achieved by a polarizing beam splitter PBS. The high-power 1.5μm pump light is focused and transmitted through a dichroic mirror DM4, a long-pass filter LPF3, and a C4 lens with a focal length of 150mm. The seed light is reflected and collinear with the pump light. The time synchronization is adjusted by a delay device Delay3 set in the optical path of the seed light.

[0023] As a preferred method, the BGGSe crystal adopts type I phase matching, its cutting angle is designed to be 24°, and the crystal size is 5mm×5mm×4mm. By continuously adjusting the angle of the BGGSe crystal in the range of 23.5° to 27°, the output laser wavelength can be continuously tunable in the range of 6μm to 18μm.

[0024] A high-power broadband tunable long-wavelength mid-infrared femtosecond laser generator is provided to implement a method for generating a high-power broadband tunable long-wavelength mid-infrared femtosecond laser, comprising:

[0025] Pumped laser source;

[0026] The beam splitting and control module is used to split and independently control the laser beam output from the pump laser source;

[0027] A 1.5μm signal light generation module includes a first YAG crystal, lens B1, lens C1, and long-pass filter LPF1, used to generate and filter out 1.5μm signal light;

[0028] The cascaded optical parametric amplifier module includes a KTP1 crystal, a KTP2 crystal, a dichroic mirror DM1, a dichroic mirror DM2, a long-pass filter LPF2, a lens C3, a dichroic mirror DM3, a dichroic mirror DM4, a long-pass filter LPF3, a half-wave plate HWP2, a thin-film polarizer TFP2, a high-reflectivity mirror HR1, a delay device Delay1, a lens B2, a half-wave plate HWP3, a thin-film polarizer TFP3, a high-reflectivity mirror HR2, a delay device Delay2, and a lens B3, used to amplify the signal light in two stages to generate high-power 1.5μm pump light;

[0029] A broadband seed light generation module, including a second YAG crystal, lens B4, lens C5 and long-pass filter LPF4, is used to generate a supercontinuum as seed light;

[0030] The beam combining and synchronization module includes a polarizing beam splitter PBS, a delay device Delay3, and a calcium fluoride lens CaF2, which are used to spatially combine and temporally synchronize the high-power 1.5μm pump light with the seed light.

[0031] Wavelength conversion and tuning module, including a BGGSe crystal and an angle adjustment mechanism;

[0032] The output filtering module is used to filter out residual pump light in the output laser.

[0033] As a preferred embodiment, the BGGSe crystal in the wavelength conversion and tuning module adopts type I phase matching, has an initial cut angle of 24°, and is mounted on a precision rotary table to achieve an angle adjustment range of 23.5° to 27°.

[0034] As a preferred embodiment, the output filtering module is a long-pass filter with a cutoff wavelength of 2.4 μm; in the broadband seed light generation module, the seed light passes sequentially through a silver mirror Ag, a delay device Delay3, and the calcium fluoride lens CaF2 before being incident on the polarizing beam splitter PBS; the high-power 1.5 μm pump light is focused by a C4 lens with a focal length of 150 mm before being incident on the polarizing beam splitter PBS.

[0035] The present invention has at least the following beneficial effects:

[0036] This invention employs a 1.5μm high-power femtosecond laser as the pump source, combined with a BGGSe nonlinear crystal for optical parametric amplification. It effectively utilizes the advantages of the BGGSe crystal's wide transmission range (0.5–18μm) and high nonlinear coefficient (d11≈66pm / V), achieving phase matching in the 6–18μm band under 1.5μm pumping conditions. This results in broadband, high-power, femtosecond-level laser output covering the long-wave mid-infrared (especially 10–16μm). Simultaneously, the pump light power is increased through two-stage cascaded optical parametric amplification, and precise synchronization with the supercontinuum seed light significantly improves conversion efficiency and output stability, solving the problems of low average power and narrow tuning range in existing long-wave mid-infrared femtosecond laser technologies. Attached Figure Description

[0037] To reveal the technical details of the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below. It should be emphasized that these drawings only present several embodiments of the present invention and should not be considered as defining the scope of the invention. For those skilled in the art, other related drawings can still be derived based on these drawings without inventive effort.

[0038] Figure 1 A schematic diagram of a high-power broadband tunable long-wavelength mid-infrared femtosecond laser;

[0039] Figure 2 This is a schematic diagram of broadband tunable phase matching under 1.5μm pumping. Detailed Implementation

[0040] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.

[0041] In the following description, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, it should be understood that the present disclosure is not limited to the specific forms shown herein. Rather, it should be understood to encompass various variations, equivalents, and / or alternatives to the embodiments of the present disclosure. In illustrating the drawings, the same reference numerals will be used to denote similar components.

[0042] In the various embodiments of this disclosure, the terms "first," "second," "the first," or "the second" are intended to modify different components and not to indicate order and / or importance, nor do they constitute a limitation on the respective components. For example, a first user equipment and a second user equipment represent different user equipments, although they both fall under the category of user equipment. Similarly, a first component may be named a second component, and a second component may be named a first component, without changing their essential attributes within the scope of this disclosure.

[0043] In this disclosure, terminology is used to describe specific embodiments and does not constitute a limitation thereof. In this context, the use of the singular form also encompasses the plural form, unless otherwise expressly stated herein. In the course of description, terms such as “comprising” or “having” are intended to indicate the presence of features, quantities, steps, operations, structural components, parts, or combinations thereof, and do not preclude the possibility or addition of one or more other features, quantities, steps, operations, structural components, parts, or combinations thereof.

[0044] It should be clarified that while the following description provides detailed specific information to aid in a comprehensive understanding of the exemplary embodiments, those skilled in the art will recognize that the exemplary embodiments can be implemented even without these specific details. For example, the system may be illustrated using block diagrams to avoid excessive detail that could obscure the clarity of the example. In other cases, to maintain the clarity of the example, unnecessary details of well-known processes, structures, and techniques may be omitted.

[0045] See Figure 1 A method for generating high-power broadband tunable long-wavelength mid-infrared femtosecond laser includes the following steps:

[0046] A femtosecond pump laser is provided and split into a first beam and a second beam;

[0047] The first beam is used to pump the first YAG crystal to generate a first supercontinuum, and a signal light of a predetermined wavelength is selected from it.

[0048] The signal light is subjected to at least two cascaded optical parametric amplification stages to generate high-power mid-infrared pump light;

[0049] The second beam is used to pump the second YAG crystal to generate a second supercontinuum covering the long-wave infrared band as a seed light.

[0050] After spatially combining and temporally synchronizing the high-power mid-infrared pump light with the seed light, they are jointly incident on a BGGSe (i.e., BaGa2GeSe6) crystal for optical parametric amplification.

[0051] By adjusting the phase matching angle of the BGGSe crystal, continuous tuning of the output wavelength is achieved, resulting in high-power, broadband tunable long-wavelength mid-infrared femtosecond laser output. To achieve precise control of the BGGSe crystal's phase matching angle, the crystal is mounted on a highly stable reflector mount equipped with precision adjustment knobs in the horizontal (left / right) and vertical (pitch) directions. Rotating these knobs finely adjusts the crystal's spatial orientation, thereby continuously changing its phase matching angle relative to the incident pump light and seed light. In practical operation, the user determines the target output wavelength by referring to... Figure 2 The phase-matching curve shown illustrates how adjusting the crystal angle to the corresponding value (e.g., approximately 25.2° for 10μm output and approximately 26.5° for 16μm output) enables efficient optical parametric amplification at the desired wavelength. This adjustment process is simple, stable, and highly repeatable, supporting continuous, non-jumping wavelength scanning across the entire 6–18μm range.

[0052] In a preferred embodiment, the femtosecond pump laser has a center wavelength of 1 μm, an average power of 100 W, a repetition frequency of 500 kHz, and a pulse width of 300 fs.

[0053] The beam splitting into a first beam and a second beam is achieved through a beam splitting unit consisting of a half-wave plate HWP1 and a thin-film polarizer TFP1.

[0054] In a preferred embodiment, the steps of generating the first supercontinuum and selecting the signal light include: focusing the first beam sequentially through an aperture Iris1 and a lens B1 into the first YAG crystal to generate a supercontinuum; after the supercontinuum is collimated by a lens C1, the residual pump light is filtered out by a long-pass filter LPF1, and then focused by a lens C2 with a focal length of 150mm to obtain a signal light with a center wavelength of 1.5μm.

[0055] In a preferred embodiment, the at least two cascaded optical parametric amplification stages specifically refer to:

[0056] The 1.5μm signal light and the 1μm pump light, which is controlled by the second beam through the half-wave plate HWP2, the thin-film polarizer TFP2, the high-reflection mirror HR1, the delay device Delay1 and the lens B2, are combined in the KTP1 crystal through the dichroic mirror DM1 for the first stage of amplification, and the output power is 200mW of 1.5μm laser.

[0057] The 1.5μm laser beam amplified in the first stage is filtered by a dichroic mirror DM2 and a long-pass filter LPF2 to remove residual pump light. Then, it passes through a 150mm focal length C3 lens and a dichroic mirror DM3. Together with the 1μm pump light generated by the second beam through a half-wave plate HWP3, a thin-film polarizer TFP3, a high-reflection mirror HR2, a delay device Delay2, and a lens B3, the beam is combined in a KTP2 crystal for the second stage amplification, producing a high-power 1.5μm pump light with an average power of 10W.

[0058] In a preferred embodiment, the step of generating the seed light includes: focusing the second beam sequentially through an aperture Iris2 and a lens B4 into the second YAG crystal to generate a second supercontinuum; the second supercontinuum is collimated by a lens C5 and filtered by a long-pass filter LPF4 to remove residual pump light, and then used as the seed light.

[0059] In a preferred embodiment, the spatial beam combining is achieved by a polarizing beam splitter PBS. The high-power 1.5μm pump light is focused and transmitted through a dichroic mirror DM4, a long-pass filter LPF3, and a C4 lens with a focal length of 150mm. The seed light is reflected and collinear with the pump light. The time synchronization is adjusted by a delay device Delay3 set in the optical path of the seed light.

[0060] Furthermore, considering the significant time-frequency coupling effect of the supercontinuum seed light generated by the second YAG crystal (i.e., different wavelength components have different arrival times), if the overall delay is achieved solely through a single delay device Delay3, it may lead to the long-wavelength seed light (e.g., 15 μm) and pump light failing to achieve optimal time overlap in the BGGSe crystal, thereby reducing conversion efficiency. Therefore, this invention introduces a wavelength-dependent dynamic delay compensation module into the seed light path, located after Delay3 and before the CaF2 lens. This module consists of a pair of anti-parallel calcium fluoride (CaF2) wedge prisms, whose relative lateral displacement Δx is electrically adjustable, thereby introducing different group delays for seed light of different wavelengths.

[0061] Experimental calibration shows that the relative group delay introduced by this module is approximately linearly related to the lateral displacement:

[0062] ;

[0063] in, The relative delay (in seconds) between the 15μm and 6μm wavelength components. The lateral misalignment of the two wedge prisms (unit: m) It is the equivalent delay factor, which is determined by material dispersion, wedge angle, and beam geometry.

[0064] For the CaF2 wedge prism (wedge angle 2°, thickness 10mm) used in this invention, the actual measurement results are as follows: That is, each micrometer of lateral displacement introduces a relative delay of about 3 fs.

[0065] when hour, Combining the inherent positive chirp of the YAG supercontinuum (with a natural lag of approximately 30-50 fs for long-wavelength components), by adjusting... This allows for synchronized compression and overlap of the 6-18μm full-band seed light with the 1.5μm pump pulse at the BGGSe crystal inlet. Experimental results show that the average output power in the 10-16μm band is increased by more than 40%, and the spectral flatness is improved by 2.1 times. This time-frequency coupling compensation structure based on dispersive wedge pairs is simple, requires no active feedback, and is significantly different from traditional fixed-delay or electronic synchronization methods.

[0066] In a preferred embodiment, the BGGSe crystal employs type I phase matching, has a dicing angle of 24°, and a crystal size of 5mm × 5mm × 4mm. By continuously adjusting the angle of the BGGSe crystal within the range of 23.5° to 27°, the output laser wavelength is continuously tunable within the range of 6μm to 18μm. See also Figure 2 The figure shows the Type I phase-matching curve of the BGGSe crystal under a 1.5μm pump light. The horizontal axis represents the wavelength of the generated mid-infrared signal light, the left vertical axis represents the phase-matching angle of the crystal relative to the incident light, and the right vertical axis represents the phase-matching efficiency, ranging from 0 to 1. As can be seen from the figure, within a tuning range of 23.5° to 27°, continuous wavelength output from 6μm to 18μm can be achieved, covering the entire long-wavelength mid-infrared molecular fingerprint region. This phase-matching curve guides the design of the initial crystal cutting angle. This invention selects 24° as the initial cutting angle of the BGGSe crystal, placing its operating point near the center of the tuning range. This ensures both broad spectral coverage and considers the optical parametric gain efficiency at each wavelength, thereby achieving high-power, broadband, and continuously tunable femtosecond laser output in actual operation.

[0067] Furthermore, to overcome the gain bandwidth compression problem caused by group velocity mismatch (GVM) in the long wavelength range (>12μm) of BGGSe crystal, this invention proposes a pump spectrum pre-shaping scheme: before the 1.5μm high-power pump light enters the BGGSe crystal, its spectral phase is controllably modulated to give it negative chirp characteristics, thereby broadening the pulse in the time domain, reducing the peak power density, and extending the effective interaction time with the seed light. Specifically, a programmable acousto-optic dispersion filter or spatial light modulator (SLM) is added in front of the C4 lens to apply secondary phase modulation to the 1.5μm pump light:

[0068] (1)

[0069] in, Angular frequency Additional spectral phase at (unit: rad / s) (unit: rad), The center angular frequency ( Therefore ), The second-order group velocity dispersion parameter (unit: Take the negative value here. ), typical range is to (Right now to ), This is a constant phase offset, which can be set to 0.

[0070] After this modulation, the time-domain broadening of the initial chirp-free Gaussian pump pulse is as follows:

[0071] (2)

[0072] In the formula, The original pulse width (FWHM) The pulse width after shaping (unit: s).

[0073] when At that time, the calculation yielded P.S. Although the peak power decreases, the BGGSe has a relatively long gain response time in the 10-16μm band (limited by GVM, the effective interaction window is about 0.8-1.5ps). The broadened pump pulse can more fully excite the long-wavelength idler light, increasing the conversion efficiency at 16μm by up to 2.3 times. At the same time, the full width at half maximum (FWHM) of the output spectrum is broadened from the original 0.8μm to 2.1μm, significantly enhancing the broadband coverage capability.

[0074] Furthermore, to suppress gain fluctuations in the BGSe crystal in the 10-18 μm band caused by enhanced absorption and non-uniformity of phase-matching bandwidth, this invention employs a synergistic optimization strategy combining dual-end opposing pumping with gradient temperature control. Specifically, the 1.5 μm pump light, after spectral pre-shaping, is split into two sub-pulses with an intensity ratio of 1:1.2, which are simultaneously injected from the input and output ends of the BGGSe crystal, respectively, allowing the long-wavelength idler light to experience a more uniform gain distribution within the crystal. Simultaneously, a multi-zone independent temperature control unit is integrated into the crystal fixture, with three temperature control zones set along the light propagation direction, exhibiting a linear temperature gradient distribution. Experiments show that when the temperature in the central region is maintained at... Temperature difference at both ends At an inlet temperature of 62°C and an outlet temperature of 68°C, the phase matching condition in the 12-16μm band is effectively equalized. The normalized gain is defined as:

[0075] ;

[0076] in, wavelength Small-signal gain coefficient at (unit: cm) -1 ), This represents the average gain in the 10-16μm band. Without this scheme, exist The value fluctuates within the range of 0.42-1.0, corresponding to a peak-to-valley ratio of 2.38; after introducing dual-end pumping and gradient temperature control, The fluctuation is narrowed to 0.78-1.0, the peak-to-valley ratio is reduced to 1.28, and the spectral flatness (characterized by the reciprocal of the peak-to-valley ratio) is improved by approximately 1.86 times. This method does not require additional nonlinear crystals or complex feedback systems; it can significantly improve the long-wavelength output consistency simply by splitting the pump optical path and managing the crystal thermally. Together with the aforementioned seed light time-frequency coupling compensation and pump pulse spectral pre-shaping, it forms a three-level synergistic control architecture, achieving ultra-wideband, highly flat, and highly efficient mid-infrared output in the 10-18 μm range.

[0077] In a preferred embodiment, the average power of the output long-wave mid-infrared femtosecond laser in the 10μm to 16μm band is not less than 100mW.

[0078] In a preferred embodiment, a long-pass filter with a cutoff wavelength of 2.4 μm is provided at the output end of the BGGSe crystal to filter out residual 1.5 μm pump light.

[0079] A high-power, broadband, tunable long-wavelength mid-infrared femtosecond laser generator, see [reference needed]. Figure 1 A method for generating a high-power, broadband, tunable long-wavelength mid-infrared femtosecond laser, comprising:

[0080] Pumped laser source;

[0081] The beam splitting and control module is used to split and independently control the laser beam output from the pump laser source;

[0082] A 1.5μm signal light generation module includes a first YAG crystal, lens B1, lens C1, and long-pass filter LPF1, used to generate and filter out 1.5μm signal light;

[0083] The cascaded optical parametric amplifier module includes a KTP1 crystal, a KTP2 crystal, a dichroic mirror DM1, a dichroic mirror DM2, a long-pass filter LPF2, a lens C3, a dichroic mirror DM3, a dichroic mirror DM4, a long-pass filter LPF3, a half-wave plate HWP2, a thin-film polarizer TFP2, a high-reflectivity mirror HR1, a delay device Delay1, a lens B2, a half-wave plate HWP3, a thin-film polarizer TFP3, a high-reflectivity mirror HR2, a delay device Delay2, and a lens B3, used to amplify the signal light in two stages to generate high-power 1.5μm pump light;

[0084] A broadband seed light generation module, including a second YAG crystal, lens B4, lens C5 and long-pass filter LPF4, is used to generate a supercontinuum as seed light;

[0085] The beam combining and synchronization module includes a polarizing beam splitter PBS, a delay device Delay3, and a calcium fluoride lens CaF2, which are used to spatially combine and temporally synchronize the high-power 1.5μm pump light with the seed light.

[0086] Wavelength conversion and tuning module, including a BGGSe crystal and an angle adjustment mechanism;

[0087] The output filtering module is used to filter out residual pump light in the output laser.

[0088] In a preferred embodiment, the pump laser source is a femtosecond laser with an output center wavelength of 1 μm, an average power of 100 W, a repetition frequency of 500 kHz, and a pulse width of 300 fs; the beam splitting and control module includes a half-wave plate HWP1 and a thin-film polarizer TFP1.

[0089] In a preferred embodiment, the cascaded optical parametric amplification module includes a pump optical path for the first stage of amplification comprising a half-wave plate HWP2, a thin-film polarizer TFP2, a high-reflectivity mirror HR1, a delay device Delay1, and a lens B2; and a pump optical path for the second stage of amplification comprising a half-wave plate HWP3, a thin-film polarizer TFP3, a high-reflectivity mirror HR2, a delay device Delay2, and a lens B3.

[0090] In a preferred embodiment, the cascaded optical parametric amplifier module includes a pump optical path for the first stage amplification comprising a half-wave plate HWP2, a thin-film polarizer TFP2, a high-reflectivity mirror HR1, a delay device Delay1, and a lens B2; and a pump optical path for the second stage amplification comprising a half-wave plate HWP3, a thin-film polarizer TFP3, a high-reflectivity mirror HR2, a delay device Delay2, and a lens B3. The purpose of this two-stage amplification design is that the first stage amplification primarily serves as a pre-amplification, enhancing signal strength and providing a higher-quality input signal for the second stage main power amplification, thereby improving overall conversion efficiency. Furthermore, this invention employs a silver mirror (Ag) for reflection and time delay adjustment of the supercontinuum spectrum. Due to its high reflectivity within the signal light range, it effectively reduces energy loss and ensures time synchronization accuracy. Simultaneously, a dichroic mirror (DM) is used to achieve beam combining and splitting of the signal and pump light, capable of both transmitting signal light and reflecting pump light, thus contributing to optimized optical path structure. Long-pass filters (LPFs) are used to filter out residual pump light and other unwanted wavelength components, ensuring the purity of the output laser.

[0091] In a preferred embodiment, the BGGSe crystal in the wavelength conversion and tuning module employs type I phase matching, has an initial cut angle of 24°, and is mounted on a precision rotary table to achieve an angle adjustment range of 23.5° to 27°.

[0092] In a preferred embodiment, the output filtering module is a long-pass filter with a cutoff wavelength of 2.4 μm; in the broadband seed light generation module, the seed light passes sequentially through a silver mirror Ag, a delay device Delay3, and the calcium fluoride lens CaF2 before being incident on the polarizing beam splitter PBS; the high-power 1.5 μm pump light is focused by a C4 lens with a focal length of 150 mm before being incident on the polarizing beam splitter PBS.

[0093] It should be noted that, Figure 1 Although the three blue optical paths shown in the diagram are drawn along similar directions, their actual optical path structure can be multiple parallel branches branching off from the second beam backbone. Each branch is spatially separated by a high-reflection mirror or beam splitter, and is used for the first-stage pump, the second-stage pump, and seed light generation, respectively, thereby achieving independent control of power distribution and time delay. Of course, in specific application scenarios, other beam distribution methods can also be used, such as cascaded beam splitter structures, as long as the power, polarization, and timing requirements of each functional module can be met.

[0094] This invention optimizes the phase-matching conditions and initial cutting angle of the BGGSe crystal and employs a 1.5μm high-power femtosecond laser for pumping, achieving broadband, continuously tunable mid-infrared femtosecond laser output within the 6–18μm range. Simultaneously, a high-power 1.5μm pump source is constructed using two-stage KTP optical parametric amplification. Combined with the high nonlinear coefficient (d11≈66pm / V) and low dispersion characteristics of the BGGSe crystal, the conversion efficiency is significantly improved, achieving an average output power of no less than 100mW in the 10–16μm long-wavelength mid-infrared band, meeting the application requirements for high-sensitivity detection of molecular fingerprint regions.

[0095] In summary, this invention proposes a systematic and practical technical solution for the efficient generation of long-wavelength mid-infrared femtosecond lasers. By using a 1.5μm high-power femtosecond laser as the pump source, combined with supercontinuum seed light generated by a YAG crystal, and achieving optical parametric amplification in the key BGGSe (BaGa2GeSe6) crystal, the highly valuable "molecular fingerprint" band of 6–18μm is successfully covered. More importantly, addressing common problems in practical operation such as timing mismatch, gain unevenness, and bandwidth limitations, we did not rely on complex external feedback systems. Instead, we started from the optical path design itself, introducing an adjustable wedge prism to compensate for the time-frequency coupling of the seed light, performing spectral pre-shaping of the pump pulse to match the long-wavelength gain window, and employing dual-end pumping combined with gradient temperature control to balance the output performance across the entire band. These measures work synergistically, not only making the laser output more stable and flatter but also significantly improving the conversion efficiency. Experimental results show that in the 10–16μm range, the system can continuously output an average power exceeding 100mW, sufficient to support practical needs such as high-sensitivity spectral detection. The entire solution balances performance and practicality, providing a reliable path for mid-infrared ultrafast laser technology to reach application scenarios beyond the laboratory.

[0096] The above description only illustrates several preferred embodiments of the present invention, aiming to clearly explain its core concept and technical implementation, and is not intended to limit the scope of protection of the present invention. Those skilled in the art, after understanding the basic principles of the present invention, can adjust, replace, or optimize the specific structure, parameters, or steps according to actual needs. Any improvements, equivalent transformations, or reasonable extensions made within the spirit and principles of the present invention should be considered to fall within the protection scope of the present invention.

Claims

1. A method for generating high-power broadband tunable long-wavelength mid-infrared femtosecond laser, characterized in that, Includes the following steps: A femtosecond pump laser is provided and split into a first beam and a second beam; The first beam is used to pump the first YAG crystal to generate a first supercontinuum, and a signal light of a predetermined wavelength is selected from it. The signal light is subjected to at least two cascaded optical parametric amplification stages to generate high-power mid-infrared pump light; The second beam is used to pump the second YAG crystal to generate a second supercontinuum covering the long-wave infrared band as a seed light. After spatially combining and temporally synchronizing the high-power mid-infrared pump light with the seed light, they are jointly incident on a BGGSe crystal for optical parametric amplification. By adjusting the phase matching angle of the BGGSe crystal, continuous tuning of the output wavelength can be achieved, resulting in high-power, broadband tunable long-wavelength mid-infrared femtosecond laser output.

2. The method for generating a high-power broadband tunable long-wavelength mid-infrared femtosecond laser according to claim 1, characterized in that, The femtosecond pump laser has a center wavelength of 1 μm, an average power of 100 W, a repetition frequency of 500 kHz, and a pulse width of 300 fs. The beam splitting into a first beam and a second beam is achieved through a beam splitting unit consisting of a half-wave plate HWP1 and a thin-film polarizer TFP1.

3. The method for generating a high-power broadband tunable long-wavelength mid-infrared femtosecond laser according to claim 1, characterized in that, The steps of generating the first supercontinuum and selecting the signal light include: focusing the first beam into the first YAG crystal sequentially through the aperture Iris1 and the lens B1 to generate a supercontinuum; after the supercontinuum is collimated by the lens C1, the residual pump light is filtered out by the long-pass filter LPF1, and then focused by the C2 lens with a focal length of 150mm to obtain the signal light with a center wavelength of 1.5μm.

4. The method for generating a high-power broadband tunable long-wavelength mid-infrared femtosecond laser according to claim 3, characterized in that, The at least two cascaded optical parametric amplifications specifically refer to: The 1.5μm signal light and the 1μm pump light, which is controlled by the second beam through the half-wave plate HWP2, the thin-film polarizer TFP2, the high-reflection mirror HR1, the delay device Delay1 and the lens B2, are combined in the KTP1 crystal through the dichroic mirror DM1 for the first stage of amplification, and the output power is 200mW of 1.5μm laser. The 1.5μm laser beam amplified in the first stage is filtered by a dichroic mirror DM2 and a long-pass filter LPF2 to remove residual pump light. Then, it passes through a 150mm focal length C3 lens and a dichroic mirror DM3. Together with the 1μm pump light generated by the second beam through a half-wave plate HWP3, a thin-film polarizer TFP3, a high-reflection mirror HR2, a delay device Delay2, and a lens B3, the beam is combined in a KTP2 crystal for the second stage amplification, producing a high-power 1.5μm pump light with an average power of 10W.

5. The method for generating a high-power broadband tunable long-wavelength mid-infrared femtosecond laser according to claim 1, characterized in that, The step of generating the seed light includes: focusing the second beam sequentially through the aperture Iris2 and the lens B4 into the second YAG crystal to generate a second supercontinuum; the second supercontinuum is collimated by the lens C5 and filtered by the long-pass filter LPF4 to remove residual pump light, and then used as the seed light.

6. The method for generating a high-power broadband tunable long-wavelength mid-infrared femtosecond laser according to claim 1, characterized in that, The spatial beam combining is achieved by a polarizing beam splitter PBS. The high-power 1.5μm pump light is focused and transmitted through a dichroic mirror DM4, a long-pass filter LPF3, and a C4 lens with a focal length of 150mm. The seed light is reflected and collinear with the pump light. The time synchronization is adjusted by a delay device Delay3 set in the optical path of the seed light.

7. The method for generating a high-power broadband tunable long-wavelength mid-infrared femtosecond laser according to claim 1, characterized in that, The BGGSe crystal uses type I phase matching, with a cutting angle of 24° and a crystal size of 5mm×5mm×4mm. By continuously adjusting the angle of the BGGSe crystal within the range of 23.5° to 27°, the output laser wavelength can be continuously tunable within the range of 6μm to 18μm.

8. A high-power broadband tunable long-wavelength mid-infrared femtosecond laser generating device, used to implement the high-power broadband tunable long-wavelength mid-infrared femtosecond laser generating method according to any one of claims 1-7, characterized in that, include: Pumped laser source; The beam splitting and control module is used to split and independently control the laser beam output from the pump laser source; A 1.5μm signal light generation module includes a first YAG crystal, lens B1, lens C1, and long-pass filter LPF1, used to generate and filter out 1.5μm signal light; The cascaded optical parametric amplifier module includes a KTP1 crystal, a KTP2 crystal, a dichroic mirror DM1, a dichroic mirror DM2, a long-pass filter LPF2, a lens C3, a dichroic mirror DM3, a dichroic mirror DM4, a long-pass filter LPF3, a half-wave plate HWP2, a thin-film polarizer TFP2, a high-reflectivity mirror HR1, a delay device Delay1, a lens B2, a half-wave plate HWP3, a thin-film polarizer TFP3, a high-reflectivity mirror HR2, a delay device Delay2, and a lens B3, used to amplify the signal light in two stages to generate high-power 1.5μm pump light; A broadband seed light generation module, including a second YAG crystal, lens B4, lens C5 and long-pass filter LPF4, is used to generate a supercontinuum as seed light; The beam combining and synchronization module, including a polarizing beam splitter PBS, a delay device Delay3, and a calcium fluoride lens CaF2, is used to spatially combine and temporally synchronize the high-power 1.5μm pump light with the seed light. Wavelength conversion and tuning module, including a BGGSe crystal and an angle adjustment mechanism; The output filtering module is used to filter out residual pump light in the output laser.

9. A high-power broadband tunable long-wavelength mid-infrared femtosecond laser generating device according to claim 8, characterized in that, The BGGSe crystal in the wavelength conversion and tuning module uses type I phase matching, has an initial cut angle of 24°, and is mounted on a precision rotary table to achieve an angle adjustment range of 23.5° to 27°.

10. A high-power broadband tunable long-wavelength mid-infrared femtosecond laser generating device according to claim 8 or 9, characterized in that, The output filtering module is a long-pass filter with a cutoff wavelength of 2.4 μm; in the broadband seed light generation module, the seed light passes sequentially through a silver mirror Ag, a delay device Delay3, and the calcium fluoride lens CaF2 before being incident on the polarizing beam splitter PBS; the high-power 1.5 μm pump light is focused by a C4 lens with a focal length of 150 mm before being incident on the polarizing beam splitter PBS.

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