High-power wide-spectrum long-wave infrared femtosecond laser generation method

Abstract

The invention provides a high-power wide-spectrum long-wave infrared femtosecond laser generation method, and relates to the technical field of infrared ultrafast laser. According to the method, the 1.5 [mu] m pumping BGSe crystal is adopted, compared with a traditional 1 [mu] m pumping BGSe crystal, the heat accumulation effect is greatly reduced, and the operation stability of the system is remarkably improved in combination with a water-cooling heat dissipation device. Through crystal cutting angle optimization and phase matching design, 10-16 [mu] m wide-spectrum long-wave infrared femtosecond laser output is achieved, the power reaches 100 mW, and the application requirements in the fields of molecular spectrum recognition, environment monitoring and the like are met.

Description

Technical Field

[0001] This invention relates to the field of infrared ultrafast laser technology, and more specifically, to a method for generating high-power broadband long-wavelength infrared femtosecond lasers. Background Technology

[0002] Long-wavelength mid-infrared (approximately 10⁻¹⁶ μm) femtosecond laser sources hold significant scientific importance and application value in fields such as molecular fingerprint spectral recognition, selective photolysis and ablation of biological tissues, strong-field physical processes, and environmental and gas monitoring. This wavelength band covers a variety of molecular fundamental vibrational absorption peaks, corresponding to the intrinsic vibrational modes of molecular structures and chemical bonds. Therefore, it places high demands on the light source in terms of spectral coverage, peak power, and temporal stability. An ideal long-wavelength mid-infrared light source should simultaneously possess a wide spectral bandwidth, high peak power, and stable femtosecond-level pulse output capability. However, due to limitations in the availability of nonlinear crystals regarding transparent windows, laser damage thresholds, group velocity dispersion, and phase-matching conditions, achieving broadband, high-power femtosecond pulse output in this band still faces significant technical challenges.

[0003] Currently, the generation of femtosecond lasers in the 10–16 μm band mainly relies on second-order nonlinear frequency conversion processes, including difference frequency generation (DFG), optical parametric amplification (OPA), and optical parametric oscillation (OPO) techniques. Commonly used nonlinear crystal materials include ZnGeP2 (ZGP), AgGaS2 (AGS), AgGaSe2 (AGSe), and GaSe. However, these crystals all have varying degrees of performance limitations in practical applications. For example, although ZGP has a large second-order nonlinear coefficient, its short-wavelength transmission cutoff is about 2 μm, and its long-wavelength cutoff at the transparent window is about 10 μm. Furthermore, its relatively narrow bandgap makes it difficult to directly pump with high-power femtosecond lasers in the 1 μm band. AGS and AGSe crystals have good transmission characteristics near 10 μm, but their nonlinear coefficients are relatively low, their birefringence effect is weak, and they exhibit significant group velocity mismatch. This typically significantly limits the optical parametric gain bandwidth, making it difficult to achieve broadband femtosecond pulse amplification and effective compression under high-power conditions. While GaSe crystals possess both a wide transmission range and a large nonlinear coefficient, their layered crystal structure results in lower mechanical strength, greater difficulty in fabrication and packaging, and strict requirements on the polarization state of incident light, hindering long-term stable operation under high average power pumping conditions. In contrast, BaGa2GeSe6 (BGGSe) and BaGa4Se7 (BGSe) crystals offer even wider transmission ranges, covering long wavelengths up to 18 μm. Although BGGSe exhibits a higher nonlinear coefficient, its fabrication process is relatively complex, making it difficult to obtain large-size crystals, and its bandgap width makes it unsuitable for 1 μm pumping.

[0004] In recent years, BGSe crystals have been considered a promising material for achieving long-wavelength mid-infrared femtosecond laser output due to their wide transmission range (approximately 0.47-18 μm), moderate second-order nonlinear coefficient, and good mechanical and thermal properties. However, existing BGSe-based OPA systems generally face limitations in output spectral bandwidth and achievable power. Specifically, on the one hand, due to limitations in crystal cutting angle design and group velocity mismatch effects, the parametric gain bandwidth at the long-wavelength end of existing systems remains limited, making it difficult to obtain broadband femtosecond pulse output covering 10-16 μm. On the other hand, under high repetition frequency and high average power pumping conditions, some systems are prone to thermal accumulation effects, thereby limiting the increase in output power and affecting long-term operational stability. Therefore, at present, long-wavelength mid-infrared femtosecond light sources based on BGSe crystals still cannot simultaneously meet the practical application requirements in terms of spectral coverage, output power, and system reliability, and further optimization in crystal design, phase matching schemes, and system architecture is urgently needed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for generating high-power broadband long-wave infrared femtosecond lasers, which addresses the shortcomings of existing technologies and solves the problems mentioned in the background.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for generating high-power, broadband, long-wavelength infrared femtosecond lasers, wherein the method utilizes a laser generating device to generate long-wavelength infrared femtosecond lasers, wherein: The laser emitting device includes the following components: a high-power pump source, a first half-wave plate, a first thin-film polarizer, a first coated high-reflection mirror, a second coated high-reflection mirror, a first dichroic mirror, a second dichroic mirror, a first KTP crystal, a second KTP crystal, a supercontinuum system, a beam splitter, a silver mirror, a third coated high-reflection mirror, a third KTP crystal, a third dichroic mirror, a BGSe crystal, a pass filter, and a spectrometer; The optical transmission axis is located at the center of all the above components; The high-power pump source pulsed laser pumps the first KTP crystal after passing through the first half-wave plate and the first thin-film polarizer, and then pumps the second KTP crystal after passing through the first coated high-reflection mirror. A high-power pump source pulsed laser pumps a third KTP crystal after passing through a second coated high-reflection mirror; A high-power pump source pulsed laser generates a supercontinuum spectrum through a supercontinuum system. The supercontinuum spectrum is split into two paths by a beam splitter. One path passes through a first KTP crystal, a first dichroic mirror, a second KTP crystal, and a second dichroic mirror to obtain a high-power 1.5μm laser. The high-power 1.5μm laser is then pumped by a third coated high-reflectivity mirror to a BGSe crystal. The other path is reflected by a silver mirror and enters the third KTP crystal. The output signal light is filtered by the third dichroic mirror to remove the high-power pump source pulsed laser before entering the BGSe crystal to generate a long-wave infrared femtosecond laser. After being filtered by a pass filter, the output light is captured by a spectrometer to determine its spectrum. It also includes a water-cooling device for dissipating heat from the BGSe crystal.

[0007] Furthermore, the pulsed laser parameters output by the high-power pump source are: power of 100W, repetition frequency of 500kHz, pulse width of 300fs, and center wavelength of 1030nm.

[0008] Furthermore, the supercontinuum system includes a second half-wave plate, a second thin-film polarizer, a pinhole aperture, a 150mm focal length lens coated with B-band, and a YAG crystal; The YAG crystal has a cylindrical structure with a diameter of 5 mm and a length of 10 mm. It is used to convert incident 1030 nm pulsed laser light into a supercontinuum.

[0009] Furthermore, the parameters of the first, second, and third KTP crystals are identical, all exhibiting type II phase matching, and their dimensions are 5×5×8mm. 3 The cutting angle is θ=44.5° and Φ=0°.

[0010] Furthermore, the first KTP crystal and the third KTP crystal have the same parameters, with a pump power of 5W and a pump and signal spot diameter of 500μm. Under type II phase matching conditions, the first KTP crystal outputs signal light with a wavelength range of 1.5μm, and the third KTP crystal outputs signal light with a wavelength range of 1716~1834nm, with an output power of 100~150mW for both.

[0011] Furthermore, the second KTP crystal has a pump power of 70W, a pump and signal spot diameter of 1.4mm, an output of 1.5μm, and a laser power of 10W.

[0012] Furthermore, the BGSe crystal has an XZ cut with a cutting angle of θ=40.5° and Φ=0°, adopts a type I phase matching type, and has a crystal length of 10mm. Under the condition of normal incidence of 1.5μm pump light, the BGSe crystal outputs a long-wave infrared femtosecond laser with a wavelength range of 10~16μm and an output power of 100mW.

[0013] The pump and signal spot diameters in the BGSe crystal amplification stage are 1.4 mm, and the pump power is 10 W. Due to the phase-matching design angle of 40.5°, the normal-incidence output is a broadband femtosecond laser with a wavelength of 10⁻¹⁶ μm. No tuning angle is required; only the time delay needs adjustment. Please refer to [reference needed]. Figure 3 .

[0014] Furthermore, the water cooling device includes a heat dissipation body, which has mounting holes for installing BGSe crystals. The heat dissipation body has a fluid channel, and the two ends of the fluid channel are respectively connected to the output pipe and return pipe of the water cooling system.

[0015] The present invention has at least the following advantages or beneficial effects: 1. BGSe crystals have a transmission range of 0.47~18μm, a moderate nonlinear coefficient, and a mature manufacturing process, enabling the production of large-size crystals and providing a foundation for broadband output.

[0016] 2. The system uses a 1.5μm pump BGSe crystal, which significantly reduces the heat accumulation effect compared to the traditional 1μm pump. Combined with a water-cooling device, it significantly improves the system's operational stability.

[0017] 3. Through crystal cutting angle optimization and phase matching design, a 10~16μm broadband long-wave infrared femtosecond laser output is achieved with a power of 100mW, meeting the application needs of molecular spectral recognition, environmental monitoring and other fields. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the laser emitting device provided by the present invention; Figure 2 These are a front view and a right view of the water-cooling device provided by the present invention; Figure 3 A broadband phase-matching design diagram of a BGSe crystal under 1.5 μm pumping provided by this invention; Figure 4 The broadband long-wavelength mid-infrared femtosecond light source spectrum provided by this invention.

[0020] Icons: 1. High-power pump source; 2. First half-wave plate; 3. First thin-film polarizer; 4. First coated high-reflection mirror; 5. First KTP crystal; 6. Second KTP crystal; 7. First dichroic mirror; 8. Second dichroic mirror; 9. Supercontinuum system; 91. Pinhole aperture; 92. 150mm focal length lens with B-band coating; 93. YAG crystal; 94. Second half-wave plate; 95. Second thin-film polarizer; 10. Beam splitter; 11. Silver mirror; 12. Second coated high-reflection mirror; 13. Third KTP crystal; 14. Third dichroic mirror; 15. BGSe crystal; 16. Pass filter; 17. Spectrometer; 18. Water cooling device; 19. Mounting hole; 20. Third coated high-reflection mirror; 21. Fluid channel. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] This application provides a method for generating high-power, broadband, long-wavelength infrared femtosecond lasers. This method utilizes a laser generating device to generate long-wavelength infrared femtosecond lasers, wherein: Please refer to Figure 1 As shown, the laser emitting device includes the following components: a high-power pump source 1, a first half-wave plate 2, a first thin-film polarizer 3, a first coated high-reflection mirror 4, a first KTP crystal 5, a second KTP crystal 6, a first dichroic mirror 7, a second dichroic mirror 8, a supercontinuum system 9, a beam splitter 10, a silver mirror 11, a second coated high-reflection mirror 12, a third coated high-reflection mirror 20, a third KTP crystal 13, a third dichroic mirror 14, a BGSe crystal 15, a pass filter 16, and a spectrometer 17.

[0023] The supercontinuum system 9 includes a pinhole aperture 91, a 150mm focal length lens 92 coated with B-band, and a YAG crystal 93. The YAG crystal 93 is a cylindrical structure with a diameter of 5mm and a length of 10mm, used to convert the incident pulsed laser into a supercontinuum.

[0024] The optical transmission axis is located at the center of each of the above components.

[0025] Furthermore, the parameters of the first KTP crystal 5, the second KTP crystal 6, and the third KTP crystal 13 are identical, all exhibiting type II phase matching, and their dimensions are 5×5×8mm. 3 The cutting angle is θ=44.5° and Φ=0°.

[0026] Furthermore, the first KTP crystal 5 and the third KTP crystal 13 have the same parameters, with a pump power of 5W and a pump and signal spot diameter of 500μm. Under type II phase matching conditions, the first KTP crystal 5 outputs signal light with a wavelength range of 1.5μm, and the third KTP crystal 13 outputs signal light with a wavelength range of 1716~1834nm, with an output power of 100~150mW for both.

[0027] Furthermore, the second KTP crystal 13 has a pump power of 70W, a pump and signal spot diameter of 1.4mm, an output of 1.5μm, and a laser power of 10W.

[0028] Furthermore, the BGSe crystal has an XZ cut with a cutting angle of θ=40.5° and Φ=0°, adopts a type I phase matching type, and has a length of 10mm. Under the condition of normal incidence of 1.5μm pump light, the BGSe crystal outputs long-wave infrared femtosecond laser with a wavelength range of 10~16μm and an output power of 100mW.

[0029] Furthermore, the first coated high-reflection mirror 4 and the second coated high-reflection mirror 12 are both 1030 nm coated high-reflection mirrors, and the third coated high-reflection mirror 20 is a 1050 nm coated high-reflection mirror.

[0030] Please refer to Figure 2 As shown, Figure 2 (a) is a front view of the water-cooling device. Figure 2 (b) is a right view of the water-cooling device. The laser generating device also includes a water-cooling device 18 for dissipating heat from the BGSe crystal 15. The water-cooling device 18 includes a heat dissipation body with mounting holes 19 for mounting the BGSe crystal 15. A fluid channel 21 is provided inside the heat dissipation body. The two ends of the fluid channel 21 are respectively connected to the output pipe and return pipe of an existing water-cooling system. The fluid absorbs heat through the fluid channel 21, thereby cooling the BGSe crystal 15.

[0031] The high-power pump source 1 outputs a pulsed laser with a power of 100W, a repetition frequency of 500kHz, a pulse width of 300fs, and a center wavelength of 1030nm. After passing through the first half-wave plate 2 and the first thin-film polarizer 3, it pumps the first KTP crystal 5. After passing through the first half-wave plate 2, the first thin-film polarizer 3, and the first coated high-reflection mirror 4, it pumps the second KTP crystal 6.

[0032] The pulsed laser from the high-power pump source 1 pumps the third KTP crystal 13 after passing through the second coated high-reflection mirror 12.

[0033] The pulsed laser from the high-power pump source 1 is first modulated by a combination of a 1030 nm second half-wave plate 94 and a second thin-film polarizer 95, resulting in a 4 W power output. This power is then focused onto a YAG crystal 93 via a pinhole aperture 91 and a 150 mm focal length lens 92 coated with a B-band coating to generate a supercontinuum. The generated supercontinuum is split into two paths by a semi-transparent beam splitter 10. One path, under type-two phase-matching conditions, outputs a high-power 1.5 μm laser pulse via a first KTP crystal 5, a first dichroic mirror 7, a second KTP crystal 6, and a second dichroic mirror 8, serving as the pump for the amplification stage of the BGSe crystal 15. Specifically, the pump and signal spot size of the first KTP crystal is 500 μm in diameter, with a pump power of 5 W. By adjusting the angle and time delay of the first KTP crystal, the amplified wavelength is positioned at 1.5 μm, resulting in an output power of 200 mW. The pump and signal spot of the second KTP crystal has a diameter of 1.4 mm and a power of 70 W. By adjusting the angle and time delay of the second KTP crystal, the amplified wavelength is located at 1.5 μm and the output power is 10 W.

[0034] Another supercontinuum beam is reflected by a silver mirror and enters the third KTP crystal. Under type II phase-matching conditions, it outputs a signal beam at 1716–1834 nm. This output signal beam is then filtered by a third dichroic mirror to remove the high-power pump source's pulsed laser before entering the BGSe crystal. The high-power 1.5 μm laser then pumps the BGSe crystal after passing through a third coated high-reflectivity mirror, generating a long-wavelength infrared femtosecond laser. This laser beam is filtered by a pass filter and then output. Its spectrum is captured by a spectrometer for determination. Please refer to [reference needed]. Figure 4 The output spectrum of the BGSe crystal amplification stage was obtained by using a spectrometer, covering 10~16 μm.

[0035] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for generating high-power broadband long-wavelength infrared femtosecond laser, characterized in that, The method utilizes a laser generating device to generate long-wavelength infrared femtosecond lasers, wherein: The laser emitting device includes the following components: a high-power pump source, a first half-wave plate, a first thin-film polarizer, a first coated high-reflection mirror, a second coated high-reflection mirror, a first dichroic mirror, a second dichroic mirror, a first KTP crystal, a second KTP crystal, a supercontinuum system, a beam splitter, a silver mirror, a third coated high-reflection mirror, a third KTP crystal, a third dichroic mirror, a BGSe crystal, a pass filter, and a spectrometer; The optical transmission axis is located at the center of all the above components; The high-power pump source pulsed laser pumps the first KTP crystal after passing through the first half-wave plate and the first thin-film polarizer, and then pumps the second KTP crystal after passing through the first coated high-reflection mirror. A high-power pump source pulsed laser pumps a third KTP crystal after passing through a second coated high-reflection mirror; A high-power pump source pulsed laser generates a supercontinuum spectrum through a supercontinuum system. The supercontinuum spectrum is split into two paths by a beam splitter. One path passes through a first KTP crystal, a first dichroic mirror, a second KTP crystal, and a second dichroic mirror to obtain a high-power 1.5μm laser. The high-power 1.5μm laser is then pumped by a third coated high-reflectivity mirror to a BGSe crystal. The other path is reflected by a silver mirror and enters the third KTP crystal. The output signal light is filtered by the third dichroic mirror to remove the high-power pump source pulsed laser before entering the BGSe crystal to generate a long-wave infrared femtosecond laser. After being filtered by a pass filter, the output light is captured by a spectrometer to determine its spectrum. It also includes a water-cooling device for dissipating heat from the BGSe crystal.

2. The method for generating a high-power broadband long-wavelength infrared femtosecond laser according to claim 1, characterized in that, The pulsed laser output parameters of the high-power pump source are: power of 100W, repetition frequency of 500kHz, pulse width of 300fs, and center wavelength of 1030nm.

3. The method for generating a high-power broadband long-wavelength infrared femtosecond laser according to claim 2, characterized in that, The supercontinuum system includes a second half-wave plate, a second thin-film polarizer, a pinhole aperture, a 150mm focal length lens with B-band coating, and a YAG crystal; The YAG crystal has a cylindrical structure with a diameter of 5 mm and a length of 10 mm. It is used to convert incident 1030 nm pulsed laser light into a supercontinuum.

4. The method for generating a high-power broadband long-wavelength infrared femtosecond laser according to claim 1, characterized in that, The parameters of the first, second, and third KTP crystals are identical, all exhibiting type II phase matching, and their dimensions are 5×5×8mm. 3 The cutting angle is θ=44.5° and Φ=0°.

5. The method for generating a high-power broadband long-wavelength infrared femtosecond laser according to claim 1, characterized in that, The first KTP crystal has the same parameters as the third KTP crystal, with a pump power of 5W and a pump and signal spot diameter of 500μm. Under type II phase matching conditions, the first KTP crystal outputs signal light with a wavelength range of 1.5μm, and the third KTP crystal outputs signal light with a wavelength range of 1716~1834nm. The output power of both is 100~150mW.

6. The method for generating a high-power broadband long-wavelength infrared femtosecond laser according to claim 1, characterized in that, The second KTP crystal has a pump power of 70W, a pump and signal spot diameter of 1.4mm, an output of 1.5μm, and a laser power of 10W.

7. The method for generating a high-power broadband long-wavelength infrared femtosecond laser according to claim 1, characterized in that, The BGSe crystal has an XZ facet with a cutting angle of θ=40.5° and Φ=0°. It adopts a type I phase matching method and has a crystal length of 10mm. Under normal incident conditions of 1.5μm pump light, the BGSe crystal outputs a long-wave infrared femtosecond laser with a wavelength range of 10~16μm and an output power of 100mW.

8. A method for generating high-power broadband long-wavelength infrared femtosecond laser according to claim 1, characterized in that, The water cooling device includes a heat sink body with mounting holes for installing BGSe crystals. The heat sink body has a fluid channel, and the two ends of the fluid channel are respectively connected to the output pipe and return pipe of the water cooling system.

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