A system and method for improving the output power of mid-infrared lasers generated in intracavity difference frequency

Abstract

A system and method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency (IPF) belongs to the field of ultrafast optics technology. The system of this invention includes a seed source, a first pulse amplification module, a spectral broadening module, a second pulse amplification module, a synchronization control module, and an IPF module. The first pulse amplification module includes, in sequence, a first isolator, a first semiconductor laser, a first wavelength division multiplexer, a first gain fiber, a second wavelength division multiplexer, and a second semiconductor laser. The second pulse amplification module includes, in sequence, a second isolator, a third semiconductor laser, a third wavelength division multiplexer, a second gain fiber, and a fiber collimator. This invention utilizes a laser amplifier to directly amplify the wavelength component required for the IPF after spectral broadening, and uses a birefringent crystal to precisely control the time delay of the pump light and signal light, thereby improving the power of the IPF mid-infrared laser. This invention also has advantages such as high conversion efficiency, simple optical path structure, and stable and reliable system.

Description

Technical Field

[0001] This invention belongs to the field of ultrafast optics technology and relates to a system and method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency. Background Technology

[0002] The mid-infrared (2-20 μm) band covers the vibrational absorption peaks of many organic and inorganic molecules, and its absorption intensity is at least an order of magnitude higher than that of the near-infrared band. Therefore, lasers in this band have important application prospects in molecular spectroscopy, biomedicine, and other fields. High-power mid-infrared lasers are required in many applications such as long-distance spectral measurement and laser diagnosis.

[0003] Currently, the main technologies for obtaining mid-infrared lasers include direct emission of doped ions, quantum cascade lasers, and parametric down-conversion. Direct emission of doped ions is limited by factors such as the absorption and emission spectral range of the gain medium, the operating wavelength and bandwidth of the mode-locking device, and the radiation wavelength of the pump source, thus restricting the wavelength range and pulse width of the output mid-infrared laser. Quantum cascade lasers can achieve a wider spectral tuning range, but the output spectral bandwidth is narrow, and the output laser pulse width is limited to the picosecond level or even wider. Parametric down-conversion utilizes the three-wave mixing effect in nonlinear crystals to generate mid-infrared laser output when the phase matching condition is met. This process does not involve heat accumulation, and broadband phase matching can achieve a wider spectral range and higher energy mid-infrared laser output. Intra-pulse difference frequency conversion, one of the parametric down-conversion techniques, optically differs the short-wavelength and long-wavelength components within a single pulse to achieve frequency down-conversion. It has advantages such as carrier envelope phase stability and does not require complex high-precision time synchronization and spatial adjustment of the pump and signal lights, making it a key technology for generating short-period, wide-bandwidth, and phase-stable mid-infrared laser pulses. Intra-pulse difference frequency generation requires a single pulse with a wide spectral range, ensuring simultaneous coverage of at least the two wavelengths needed for the difference frequency. Since the emission spectral width of the gain medium is limited, it is typically necessary to broaden the spectrum of the single pulse directly emitted by the laser. Common methods for broadening the single pulse spectrum include using a high peak power mode-locked laser as the driving source, broadening the spectrum through self-phase modulation via highly nonlinear fiber, or generating Raman solitons through anomalous dispersion fiber to shift the wavelength to the desired spectral range. This structure results in only a small portion of the driving source's energy being transferred to the two effective wavelengths generated in the mid-infrared region; the vast majority of the driving source's energy is wasted on unwanted wavelength components, leading to extremely low mid-infrared generation efficiency. To improve the mid-infrared laser output power generated by intra-pulse difference frequency generation, the current common practice is to increase the peak power of the driving source to increase the power of the two effective difference frequency wavelength components generated by spectral broadening. This also faces the problem of extremely low mid-infrared conversion efficiency. Furthermore, due to the limitation of conversion efficiency, a significant increase in the peak power of the driving source greatly increases system complexity, reduces system stability and reliability, and limits its application in many scenarios. Summary of the Invention

[0004] To address the problems of low conversion efficiency, reduced stability, or decreased reliability in mid-infrared laser generation caused by increasing the peak power of the driving source to increase the effective wavelength component power generated by the spread spectrum in existing intra-pulse difference frequency generation processes, the present invention aims to provide a system and method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency generation. This invention utilizes a laser amplifier to directly amplify the wavelength component required for the spread spectrum difference frequency generation, and employs a birefringent crystal to precisely control the time delay of the pump light and signal light, thereby achieving an increase in the power of mid-infrared laser generation by intra-pulse difference frequency generation. The invention also boasts advantages such as high conversion efficiency, simple optical path structure, and stable and reliable system.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] On one hand, the present invention discloses a system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency, comprising a seed source, a first pulse amplification module, a spectral broadening module, a second pulse amplification module, a synchronization control module, and a self-difference frequency module.

[0007] The seed source is preferably a mode-locked solid-state laser or a mode-locked fiber laser.

[0008] The operating wavelength of the seed source is in the near-infrared wavelength range.

[0009] The first pulse amplification module includes a first isolator, a first semiconductor laser, a first wavelength division multiplexer, a first gain fiber, a second wavelength division multiplexer, and a second semiconductor laser arranged sequentially.

[0010] The spectral broadening module is preferably a highly nonlinear optical fiber, used to generate the effective wavelength components required for difference frequencies.

[0011] The second pulse amplification module includes a second isolator, a third semiconductor laser, a third wavelength division multiplexer, a second gain fiber, and a fiber collimator arranged sequentially.

[0012] The third wavelength division multiplexer in the second pulse amplification module is preferably a broadband wavelength division multiplexer. The broadband wavelength division multiplexer components are replaceable, and the self-difference frequency can be adjusted to meet the requirements of different wavelength lasers.

[0013] The synchronization control module includes an achromatic half-wave plate, a first bicolor half-wave plate, a birefringent material, and a second bicolor half-wave plate arranged sequentially.

[0014] The first and second dual-color half-wave plates in the synchronization control module are preferably multi-level half-wave plates, used to generate an odd multiple delay of half a wavelength for one effective wavelength component required for the self-difference frequency, and an even multiple delay of half a wavelength for the other effective wavelength component.

[0015] The self-differential frequency module includes a first off-axis parabolic mirror, a nonlinear crystal, a second off-axis parabolic mirror, and a filter arranged sequentially.

[0016] The nonlinear crystal in the self-difference frequency module is preferably a quasi-phase-matched nonlinear crystal, such as a periodically polarized lithium niobate crystal or an orientation-patterned gallium phosphide crystal.

[0017] On the other hand, the present invention discloses a method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency, which is based on the system implementation of the aforementioned method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency. A method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency includes the following steps:

[0018] The seed source, first pulse amplification module, spectral broadening module, second pulse amplification module, synchronization control module, and self-differential frequency module are sequentially deployed.

[0019] The near-infrared seed laser emitted from the seed source is nonlinearly amplified by the first pulse amplification module, and the spectrum is broadened by the spectral broadening module to generate the wavelength laser component required for the intra-pulse self-difference frequency. The frequencies of the laser components are denoted as f. a and f b The second pulse amplification module amplifies the relatively low-power laser component (such as f). b Power amplification is performed.

[0020] The polarization direction of the amplified broadband laser is controlled by the achromatic half-wave plate in the synchronization control module, aligning the laser polarization direction with the polarization direction of the nonlinear crystal; the laser component f is controlled by the first dichroic half-wave plate. b The polarization direction is rotated 90° around the transmission direction, so that the laser component f a The polarization direction remains unchanged; the laser components with mutually perpendicular polarization directions f a and f b Using birefringent materials, a time delay Δt = L / c·(n) is obtained. a -n b This is used to precisely control the time delay before the self-difference frequency of two laser components in a nonlinear crystal, where L is the length of the birefringent material, c is the speed of light in vacuum, and n... a and n b These are the laser components f a and f b The refractive index in birefringent materials. The laser pulse component f, with precise time delay control via a second two-color half-wave plate. b The polarization direction is rotated 90° in the opposite direction, so that the laser component f a and f b The polarization directions coincide and are aligned with the polarization direction of the nonlinear crystal.

[0021] The laser pulse, with its time delay precisely controlled, is focused onto the nonlinear crystal through the first off-axis parabolic mirror in the self-difference frequency module, generating a wavelength f through self-difference frequency generation. a ·f b / |f a -f b The high-power mid-infrared laser is collimated by the second off-axis parabolic mirror and the remaining near-infrared laser is filtered out by a filter to output mid-infrared laser.

[0022] Beneficial effects:

[0023] 1. This invention discloses a system and method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency. It utilizes a laser amplifier to directly amplify the wavelength component required for the spread-spectrum difference frequency, employs a birefringent crystal to quantitatively control the time delay of the pump light and signal light, and utilizes a two-color waveplate to optimize the polarization direction of the pump light and signal light, thereby achieving optimal matching with the polarization direction of the nonlinear crystal. This results in an increase in the power generated by intra-pulse difference frequency mid-infrared laser. Therefore, this invention provides a technical solution with high conversion efficiency, simple optical path structure, and stable and reliable system for improving the power of mid-infrared lasers based on intra-pulse difference frequency.

[0024] 2. The present invention discloses a system and method for improving the output power of mid-infrared laser generated by pulse difference frequency. The nonlinear crystal in the pulse difference frequency module is a quasi-phase-matched nonlinear crystal, such as periodically polarized lithium niobate or patterned gallium phosphide crystal. Compared with other phase-matching methods, it has the advantages of high conversion efficiency and wide tuning range. It can flexibly design the polarization period to adapt to different mid-infrared wavelength requirements.

[0025] 3. The present invention discloses a system and method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency. By amplifying the wavelength component required for the difference frequency after spectral expansion, the output power of mid-infrared laser generated by intra-pulse difference frequency is improved. The present invention does not depend on the wavelength of the near-infrared seed source used in the embodiments, and therefore is applicable to near-infrared light sources of various optical bands. Attached Figure Description

[0026] Figure 1 A schematic diagram of a system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency according to the present invention;

[0027] Among them: 11-seed source, 21-first isolator, 22-first semiconductor laser, 23-first wavelength division multiplexer, 24-first gain fiber, 25-second wavelength division multiplexer, 26-second semiconductor laser, 31-polarity-maintaining high nonlinear fiber, 41-second isolator, 42-third semiconductor laser, 43-third wavelength division multiplexer, 44-second gain fiber, 45-fiber collimator, 51-achromatic half-wave plate, 52-first two-color half-wave plate, 53-birefringent material, 54-second two-color half-wave plate, 61-first off-axis parabolic mirror, 62-nonlinear crystal, 63-second off-axis parabolic mirror, 64-filter. Detailed Implementation

[0028] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0029] Example 1:

[0030] This embodiment discloses a system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency, which consists of a seed source 1, a first pulse amplification module 2, a spectral broadening module 3, a second pulse amplification module 4, a synchronization control module 5, and a self-difference frequency module 6.

[0031] The seed source 1 is a mode-locked fiber laser with a center wavelength of 1560nm.

[0032] The first pulse amplification module 2 includes a first isolator 21, a first semiconductor laser 22, a first wavelength division multiplexer 23, a first gain fiber 24, a second wavelength division multiplexer 25, and a second semiconductor laser 26 arranged sequentially.

[0033] The first gain fiber 24 in the first pulse amplification module 2 is a polarization-maintaining erbium-doped gain fiber.

[0034] The spectral broadening module 3 is preferably a polarization-maintaining high nonlinear fiber 31, used to generate the effective wavelength components required for difference frequencies.

[0035] The second pulse amplification module 4 includes a second isolator 41, a third semiconductor laser 42, a third wavelength division multiplexer 43, a second gain fiber 44, and a fiber collimator 45 arranged sequentially.

[0036] The third wavelength division multiplexer 43 in the second pulse amplification module 4 is a broadband wavelength division multiplexer, and the preferred transmission spectrum range is 1000-1600nm.

[0037] The second gain fiber 44 in the second pulse amplification module 4 is a polarization-maintaining ytterbium-doped gain fiber.

[0038] The synchronization control module 5 includes an achromatic half-wave plate 51, a first bicolor half-wave plate 52, a birefringent material 53, and a second bicolor half-wave plate 54 arranged sequentially.

[0039] The preferred operating wavelength range of the achromatic half-wave plate 51 in the synchronization control module 5 is 900-2000nm.

[0040] The first two-color half-wave plate 52 and the second two-color half-wave plate 54 in the synchronization control module 5 are preferably multi-level half-wave plates. The multi-level half-wave plates generate an odd multiple delay of half the wavelength for the 1030nm laser required for the self-difference frequency and an even multiple delay of half the wavelength for the 1560nm laser.

[0041] The birefringent material 53 in the synchronous control module 5 is preferably magnesium fluoride (MgF2) crystal.

[0042] The self-differential frequency module 6 includes a first off-axis parabolic mirror 61, a nonlinear crystal 62, a second off-axis parabolic mirror 63, and a filter 64 arranged sequentially.

[0043] The nonlinear crystal 62 in the self-differential frequency module 6 is preferably a periodically polarized lithium niobate crystal among quasi-phase-matching nonlinear crystals.

[0044] This embodiment also discloses a method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency in the above-mentioned system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency. The specific implementation steps are as follows:

[0045] The following modules are sequentially configured: seed source 1, first pulse amplification module 2, spectral broadening module 3, second pulse amplification module 4, synchronization control module 5, and self-differential frequency module 6.

[0046] The seed laser with a center wavelength of 1560nm emitted by the seed source 1 is nonlinearly amplified by the first pulse amplification module 2, and the spectrum is broadened by the polarization-maintaining high nonlinear fiber 31 in the spectral broadening module 3 to generate the wavelength laser component of 1030nm required for the intrapulse self-difference frequency. The relatively low-power 1030nm laser component is then amplified by the second pulse amplification module 4.

[0047] The achromatic half-wave plate 51 in the synchronization control module 5 controls the polarization direction of the amplified broadband laser, aligning the laser polarization direction with the polarization direction of the periodically polarized lithium niobate crystal in the nonlinear crystal 62. The first dichromatic half-wave plate 52 rotates the polarization direction of the 1030nm laser component by 90° around the transmission direction, keeping the polarization direction of the 1560nm laser component unchanged. The 1030nm and 1560nm laser components with mutually perpendicular polarization directions are passed through the birefringent magnesium fluoride (MgF2) crystal 53 to obtain a time delay Δt = L / c·(ne -n o This is used to precisely control the time delay before the self-difference frequency of two laser components in a nonlinear crystal, where L is the length of the birefringent material, c is the speed of light in vacuum, and n... e and n o These represent the refractive indices of the laser components at 1030 nm and 1560 nm in the birefringent material, respectively. Since MgF2 crystal is a positive uniaxial crystal (n... e >n o Therefore, the birefringent 53MgF2 crystal enables precise control of the time delay of the 1030nm and 1560nm laser components in the negatively chirped pulse. Using the second dichroic half-wave plate 54, the polarization direction of the 1030nm laser component, after precise time delay control, is rotated 90° in the opposite direction, so that the polarization directions of the 1030nm and 1560nm laser components coincide and are aligned with the polarization direction of the periodically polarized lithium niobate crystal of the nonlinear crystal 62.

[0048] The laser pulse with precise time delay is focused into the nonlinear crystal 62 by the first off-axis parabolic mirror 61 in the self-difference frequency module 6. A high-power mid-infrared laser with a wavelength of 3031.7nm is generated by the self-difference frequency. After collimation by the second off-axis parabolic mirror 63 and filtering out the remaining near-infrared laser by the filter 64, the mid-infrared laser is output.

[0049] The terms "first" and "second" used in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0050] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. 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 system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency, characterized in that: It includes a seed source, a first pulse amplification module, a spectral broadening module, a second pulse amplification module, a synchronization control module, and a self-differential frequency module; The operating wavelength of the seed source is in the near-infrared wavelength range; The first pulse amplification module includes a first isolator, a first semiconductor laser, a first wavelength division multiplexer, a first gain fiber, a second wavelength division multiplexer, and a second semiconductor laser arranged sequentially. The spectral broadening module is used to generate the effective wavelength components required for the difference frequency. The second pulse amplification module includes a second isolator, a third semiconductor laser, a third wavelength division multiplexer, a second gain fiber, and a fiber collimator arranged sequentially; the frequencies of the laser components are denoted as f. a and f b The relatively low-power laser component is amplified by the second pulse amplification module; The third wavelength division multiplexer in the second pulse amplification module is a broadband wavelength division multiplexer. By replacing the broadband wavelength division multiplexer components, the self-difference frequency can be adapted to the requirements of different wavelength lasers. The synchronization control module includes an achromatic half-wave plate, a first bichromatic half-wave plate, a birefringent material, and a second bichromatic half-wave plate arranged sequentially; it controls the polarization of mutually perpendicular laser components f. a and f b Using birefringent materials, a time delay Δt = L / c·(n) is obtained. a -n b This is used to precisely control the time delay before the self-difference frequency of two laser components in a nonlinear crystal, where L is the length of the birefringent material, c is the speed of light in vacuum, and n... a and n b These are the laser components f a and f b Refractive index in birefringent materials; The first and second dual-color half-wave plates in the synchronization control module are multi-level half-wave plates, used to generate an odd multiple delay of half a wavelength for one effective wavelength component required for the self-difference frequency, and to generate an even multiple delay of half a wavelength for the other effective wavelength component. The self-differential frequency module includes a first off-axis parabolic mirror, a nonlinear crystal, a second off-axis parabolic mirror, and a filter arranged sequentially.

2. The system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency as described in claim 1, characterized in that: The seed source is a mode-locked solid-state laser or a mode-locked fiber laser.

3. The system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency as described in claim 1, characterized in that: The spectral broadening module is selected as a highly nonlinear optical fiber.

4. The system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency as described in claim 1, characterized in that: The third wavelength division multiplexer in the second pulse amplification module is selected as a broadband wavelength division multiplexer.

5. The system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency as described in claim 1, characterized in that: The nonlinear crystal in the self-difference frequency module is selected as a quasi-phase-matched nonlinear crystal.

6. The system for improving the output power of mid-infrared laser generated by intra-pulse difference frequency as described in claim 5, characterized in that: The quasi-phase-matched nonlinear crystal includes periodically polarized lithium niobate crystals and oriented patterned gallium phosphide crystals.

7. A method for improving the output power of mid-infrared laser generated by intra-pulse difference frequency, based on the system implementation of improving the output power of mid-infrared laser generated by intra-pulse difference frequency as described in claim 1 or 2, characterized in that: Includes the following steps, The seed source, first pulse amplification module, spectral broadening module, second pulse amplification module, synchronization control module, and self-differential frequency module are deployed sequentially. The near-infrared seed laser emitted from the seed source is nonlinearly amplified by the first pulse amplification module, and the spectrum is broadened by the spectral broadening module to generate the wavelength laser component required for the intra-pulse self-difference frequency. The frequencies of the laser components are denoted as f. a and f b The relatively low-power laser component is amplified by the second pulse amplification module; The polarization direction of the amplified broadband laser is controlled by the achromatic half-wave plate in the synchronization control module, aligning the laser polarization direction with the polarization direction of the nonlinear crystal; the laser component f is controlled by the first dichroic half-wave plate. b The polarization direction is rotated 90° around the transmission direction, so that the laser component f a The polarization direction remains unchanged; the laser components with mutually perpendicular polarization directions f a and f b Using birefringent materials, a time delay Δt = L / c·(n) is obtained. a -n b This is used to precisely control the time delay before the self-difference frequency of two laser components in a nonlinear crystal, where L is the length of the birefringent material, c is the speed of light in vacuum, and n... a and n b These are the laser components f a and f b The refractive index in birefringent materials; the laser pulse component f after precise time delay control via a second two-color half-wave plate. b The polarization direction is rotated 90° in the opposite direction, so that the laser component f a and f b The polarization directions coincide and are aligned with the polarization direction of the nonlinear crystal; The laser pulse, with its time delay precisely controlled, is focused onto the nonlinear crystal through the first off-axis parabolic mirror in the self-difference frequency module, generating a wavelength f through self-difference frequency generation. a ·f b / |f a -f b The high-power mid-infrared laser is collimated by the second off-axis parabolic mirror and the remaining near-infrared laser is filtered out by a filter to output mid-infrared laser.

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