A high-energy pulsed laser system based on spatiotemporal mode locking

Abstract

The application relates to a high-energy pulse laser system based on space-time mode locking, belonging to the technical field of optoelectronic devices, and having the structure that the output end of a seed pulse source is connected with the input end of a preprocessing module, the output end of the preprocessing module is connected with the input end of an energy amplification module, and the output end of the energy amplification module is connected with the input end of a spectrum shift module. The application uses a step refractive index multimode optical fiber as a gain optical fiber and a gradually changed refractive index multimode optical fiber as a passive optical fiber to construct a space-time mode locking fiber laser, and uses a liquid crystal spatial light modulator to design a programmable pulse shaping structure to perform in-cavity high-order dispersion management, so that pure quartic space-time mode locking pulse output is realized. The pure quartic space-time mode locking pulse has the advantages of high energy, high power and narrow pulse width. Through further energy amplification and spectrum shift, high-energy ultrashort ultraviolet pulses are obtained, which are suitable for industrial precision cold processing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optoelectronic devices, and particularly relates to a high-energy pulse laser system based on space-time mode locking. BACKGROUND

[0002] Ultraviolet light band laser, especially laser in the 320-400 nm wavelength range, has important application value in the fields of precision machining, semiconductor manufacturing, scientific research and biomedical treatment. Ultraviolet laser shows unique "cold processing" advantages in laser precision machining due to its short wavelength and high photon energy. In modern industry, with the development of electronic products towards miniaturization and integration, the demand for micron-level, low-thermal-impact fine processing of heat-sensitive materials (such as flexible circuit boards, engineering plastics, glass and silicon wafers) is increasingly urgent. Traditional fiber lasers and solid-state lasers mainly work in the near-infrared wavelength, and rely on thermal effects when processing such materials, which can easily cause material deformation, melting and thermal stress cracking, and is difficult to meet the high-precision demand. In contrast, ultraviolet laser has a short wavelength and high single-photon energy, which can directly break the molecular chemical bonds of the material, realize the formation of gaseous particles or microparticles in the irradiated area, and cause photochemical ablation process, without obvious impact on the surrounding substances, with minimal thermal impact area, thereby having significant advantages in processing edge quality, processing precision and avoiding material damage, and being an ideal laser source for high-end precision cold processing.

[0003] At present, the main ways to generate ultraviolet laser are as follows: helium-cadmium laser, frequency doubling technology of all-solid-state laser and excimer laser. Although the helium-cadmium laser can directly output 325 nm or 442 nm wavelength laser, it has the problems of large size, low efficiency, short service life and limited output power. The excimer laser can generate high-power ultraviolet pulses, but its beam quality is poor, the pulse repetition frequency is low, and the gas consumption will lead to high cost, which is difficult to meet the demand of industrial processing. By frequency doubling of infrared all-solid-state laser is a mature scheme to obtain ultraviolet laser, but its system is complex, and the conversion efficiency decreases significantly with the increase of power.

[0004] In summary, the existing system capable of generating high-power ultraviolet pulse for industrial precision cold processing still needs to be further improved. SUMMARY

[0005] In order to overcome the low pulse power, wide pulse width and poor stability and other defects generated by a traditional system, the application provides a high-energy pulse laser system based on space-time mode locking and capable of being used for cold processing, high-power and narrow-pulse-width ultrashort pulses are obtained through a seed pulse source, pulse chirp adjustment is realized through a preprocessing module, pulse power amplification is realized through an energy amplification module, ultraviolet light pulses are obtained through a spectrum shifting module, so that high-power ultraviolet light pulses capable of being used for industrial precise cold processing are obtained.

[0006] The application achieves the purpose by the following technical scheme.

[0007] The high-energy pulse laser system based on space-time mode locking has the structure that the output end of the seed pulse source 1 is connected with the input end of the preprocessing module 2, the output end of the preprocessing module 2 is connected with the input end of the energy amplification module 3, and the output end of the energy amplification module 3 is connected with the input end of the spectrum shifting module 4; the seed pulse source 1 adopts a step refractive index multimode optical fiber as a gain medium and simultaneously adopts a graded refractive index multimode optical fiber as a passive optical fiber; a section of few-mode optical fiber with a fiber core diameter of 20 µm is fused after the graded refractive index multimode optical fiber with a fiber core diameter of 50 µm, and the spatial filtering function is realized by the core diameter difference between the two; a programmable pulse shaping structure is integrated inside the seed pulse source 1, the programmable pulse shaping structure is composed of a pair of diffraction gratings, a pair of lenses and a liquid crystal spatial light modulator; the energy amplification module 3 contains a pulse splitter based on beam splitting delay and a pulse synthesizer, both of which adopt the same optical configuration and are composed of 2 polarization beam splitters and 2 high-reflectivity mirrors; the spectrum shifting module 4 contains two kinds of nonlinear crystals and a tapered amplifier with a tapered section capable of keeping high beam quality, the two kinds of nonlinear crystals are LBO biaxial crystal with the characteristics of wide light transmission range, high damage threshold and high conversion efficiency and KBBF negative uniaxial crystal realizing phase matching through prism coupling.

[0008] The specific structure of the seed pulse source 1 is as follows: the pump source 101 is connected with the input end of the mode field adapter 102, the output end of the mode field adapter 102 is connected with the 980 nm end of the wavelength division multiplexer 103, the 1550 nm end of the wavelength division multiplexer 103 is connected with the input end of the fiber coupler 105 through the first erbium-doped fiber 104, the 80% output end of the fiber coupler 105 is connected with the input end of the three-ring fiber polarization controller 106, the output end of the three-ring fiber polarization controller 106 is connected with the input end of the polarization-dependent isolator 107, the output end of the polarization-dependent isolator 107 is connected with the input end of the squeezed polarization controller 108, the output end of the squeezed polarization controller 108 is connected with the input end of the first collimator 109, the optical pulse is incident to the first mirror 110 through the first collimator 109, the first mirror 110 reflects the optical pulse to the first grating 111, the optical pulse output by the first grating 111 is transmitted to the second grating 115 through the first convex lens 112, the liquid crystal spatial light modulator 113 and the second convex lens 114, the second grating 115 reflects the optical pulse to the second mirror 116, and then the second mirror 116 reflects the optical pulse to the second collimator 117. The second collimator 117 is connected with the common end of the wavelength division multiplexer 103. The optical pulse is output from the 20% output end of the fiber coupler 105;

[0009] The pre-processing module 2 has the following optical path structure: the optical pulse is incident to the third collimator 201, and then is incident to the third mirror 205 through the first isolator 202, the first half-wave plate 203 and the first filter 204 in sequence. The pump light generated by the photodiode 206 is combined with the optical pulse incident to the dichroic mirror 209 before through the fourth collimator 207 and the third convex lens 208. The combined optical pulse is incident to the fourth convex lens 210, and then is incident to the fourth mirror 215 through the fifth collimator 211, the second erbium-doped fiber 212, the sixth collimator 213 and the fifth convex lens 214 in sequence. The fourth mirror 215 reflects the optical pulse to the fifth mirror 216, and then the fifth mirror 216 reflects the optical pulse to the second half-wave plate 217. Subsequently, the optical pulse is incident to the first polarization beam splitter 220 through the first quarter-wave plate 218 and the third half-wave plate 219 in sequence. The first polarization beam splitter 220 reflects the main pulse to the first high-reflectivity mirror 222, and transmits the stray light to the first light block 221 for absorption. The first high-reflectivity mirror 222 transmits the main pulse to the grating pair composed of the third grating 223 and the fourth grating 224, and further transmits the main pulse to the first corner mirror 225. The first corner mirror 225 reflects the optical pulse back to the fourth grating 224, and then the optical pulse passes through the fourth grating 224 and the third grating 223 again, and is finally reflected and output by the first high-reflectivity mirror 222;

[0010] The energy amplification module 3 has the following optical path structure: the light pulse is incident to the second polarizing beam splitter 302 through the fourth half-wave plate 301, and is divided into transmitted light and reflected light with equal intensity, wherein the reflected light is transmitted to the third polarizing beam splitter 305 after being reflected by the second high-reflection mirror 303 and the third high-reflection mirror 304; and the transmitted light is directly transmitted to the third polarizing beam splitter 305, and the two beams of light are combined at the third polarizing beam splitter 305. The combined light pulse is sequentially transmitted through the fifth half-wave plate 306 and the fourth polarizing beam splitter 307, and is again divided by the fourth polarizing beam splitter 307 into transmitted light and reflected light with equal intensity. The reflected light is reflected by the fourth high-reflection mirror 308 and the fifth high-reflection mirror 309, and is combined with another light pulse transmitted by the fourth polarizing beam splitter 307 at the fifth polarizing beam splitter 310. The combined light pulse is incident to the fiber amplifier 311 for energy amplification. The amplified light pulse is reflected by the sixth mirror 312 to the sixth half-wave plate 313, and then is incident to the sixth polarizing beam splitter 314 and is divided into two beams of light pulses with equal intensity and orthogonal polarization. One of the two beams of light pulses is incident to the seventh mirror 316 through the second quarter-wave plate 315, and then returns to the sixth polarizing beam splitter 314, while the other beam of light pulse is incident to the eighth mirror 318 through the third quarter-wave plate 317, and also returns to the sixth polarizing beam splitter 314, and then the two beams of light pulses are combined into one beam of light pulse which is transmitted from the sixth polarizing beam splitter 314 to the seventh half-wave plate 319. The combined light pulse is incident to the seventh polarizing beam splitter 320 through the seventh half-wave plate 319, and is again divided into two beams of light pulses with equal intensity and orthogonal polarization. One of the two beams of light pulses is incident to the ninth mirror 322 through the fourth quarter-wave plate 321, and then returns to the seventh polarizing beam splitter 320, while the other beam of light pulse is incident to the tenth mirror 324 through the fifth quarter-wave plate 323, and also returns to the seventh polarizing beam splitter 320, and then the two beams of light pulses are combined into one beam of light pulse which is transmitted from the seventh polarizing beam splitter 320 to the eighth half-wave plate 325. The light pulse is incident to the eighth polarizing beam splitter 326 through the eighth half-wave plate 325, and the eighth polarizing beam splitter 326 reflects the main pulse to the second filter 328, and transmits the stray light to the second light block 327 for absorption. The filtered main pulse is reflected by the sixth high-reflection mirror 329 to the fifth grating 330, and then is incident to the second corner mirror 332 after passing through the grating pair composed of the fifth grating 330 and the sixth grating 331. The light pulse returns to the original path, passes through the grating pair again, is received by the sixth high-reflection mirror 329 and transmitted to the third filter 333, and is finally reflected and output by the eleventh mirror 334;

[0011] The spectrum shift module 4 has the following optical path structure: the light pulse is incident to the second isolator 401, first passes through the second isolator 401, the ninth half-wave plate 402, the sixth convex lens 403, enters the semiconductor optical amplifier 404 for amplification. The amplified light pulse passes through the seventh convex lens 405, the first cylindrical lens 406, the first prism 407, the second prism 408, the eighth convex lens 409, the third isolator 410, the tenth half-wave plate 411 in turn, is reflected to the first plane mirror 413 by the twelfth reflecting mirror 412. The light pulse is transmitted to the second concave mirror 422 after being transmitted through the first plane mirror 413, the first concave mirror 420 and the LBO crystal 421. The second concave mirror 422 reflects the fundamental frequency light pulse back to the first plane mirror 413 for continuous circulation, and the light pulse reflected by the first plane mirror 413 passes through the thirteenth reflecting mirror 414 and the eleventh half-wave plate 415 in turn and is transmitted to the ninth polarization beam splitter 416. The light pulse is divided into two pulses with equal intensity and orthogonal polarization, which are received by the first photodetector 417 and the second photodetector 418 respectively, for real-time monitoring of the cavity state. The second concave mirror 422 transmits the frequency-doubled light to the second cylindrical lens 423, which passes through the fourteenth reflecting mirror 424, the third cylindrical lens 425 and the twelfth half-wave plate 426 in turn and is transmitted to the second plane mirror 427. The light pulse is transmitted to the fourth concave mirror 436 after being transmitted through the second plane mirror 427, the second piezoelectric ceramic plane mirror 433, the third concave mirror 434 and the KBBF crystal 435. The fourth concave mirror 436 reflects the fundamental frequency light pulse back to the second plane mirror 427 for continuous circulation, and the light pulse reflected by the second plane mirror 427 passes through the fifteenth reflecting mirror 428 and the thirteenth half-wave plate 429 in turn and is transmitted to the tenth polarization beam splitter 430. The light pulse is divided into two pulses with equal intensity and orthogonal polarization, which are received by the third photodetector 431 and the fourth photodetector 432 respectively, for real-time monitoring of the cavity state. Finally, the spectrum shift is realized in the KBBF crystal 435, and the ultraviolet laser output is generated.

[0012] Advantages:

[0013] 1. The step refractive index multimode optical fiber is used as the gain optical fiber, and the gradually changed refractive index multimode optical fiber is used as the passive optical fiber, so that the time-space mode-locked pulse output is realized.

[0014] 2. The liquid crystal spatial light modulator is used to design the programmable pulse shaping structure to manage the high-order dispersion in the cavity of the time-space mode-locked fiber laser, and the pure fourth-order time-space mode-locked pulse output is realized.

[0015] 3. The pre-processing module is used to adjust the chirp amount of the light pulse and compress the spectrum width of the light pulse, so that the optical device after amplification can be effectively prevented from being damaged.

[0016] 4. The application uses nonlinear crystal LBO and KBBF to design a center wavelength shift structure for nonlinear frequency conversion, and realizes ultraviolet pulse output. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the overall structure block diagram of the application.

[0018] Figure 2 is the seed pulse source optical path diagram used by the application.

[0019] Figure 3 is the pre-processing module optical path diagram used by the application.

[0020] Figure 4 is the energy amplification module optical path diagram used by the application.

[0021] Figure 5 is the spectrum shift module optical path diagram used by the application.

[0022] Figure 6 is the light spot diagram of the pulse output by the seed pulse source 1.

[0023] Figure 7 is the spectrum diagram of the pulse output by the seed pulse source 1.

[0024] Figure 8 is the time domain diagram of the pulse output by the seed pulse source 1.

[0025] Figure 9 is the light spot diagram of the final output pulse.

[0026] Figure 10 is the spectrum diagram of the final output pulse.

[0027] Figure 11 is the time domain diagram of the final output pulse. DETAILED DESCRIPTION

[0028] The working principle of the application will be further described below in combination with the drawings, and it should be understood that the parameters marked in the brackets of each embodiment are preferred parameters, not a limitation on the scope of protection.

[0029] Embodiment 1 Overall structure of the application

[0030] As shown in Figure 1 , the overall structure of the application has that the output end of the seed pulse source 1 is connected with the input end of the pre-processing module 2, the output end of the pre-processing module 2 is connected with the input end of the energy amplification module 3, and the output end of the energy amplification module 3 is connected with the input end of the spectrum shift module 4.

[0031] Embodiment 2 Seed pulse source

[0032] The structure of the seed pulse source 1 is as shown inFigure 2As shown, the pump source 101 (980 nm single-mode pump light source, maximum single-mode output optical power is 1 W) is connected with the input end of the mode field adapter 102 (MCMFA-1064-F-1-H1-20 / 130 / 08D-10 mode field adapter), the output end of the mode field adapter 102 (MCMFA-1064-F-1-H1-20 / 130 / 08D-10 mode field adapter) is connected with the 980 nm end of the wavelength division multiplexer 103 (MCFWDM-9855-1-H1 / 20 / 130 / 08D-10-L-N few-mode fiber wavelength division multiplexer), the 1550 nm end of the wavelength division multiplexer 103 (MCFWDM-9855-1-H1 / 20 / 130 / 08D-10-L-N few-mode fiber wavelength division multiplexer) is connected with the input end of the fiber coupler 105 (MCMMFC-12-1550-20-L-OM4-10-L-N / FA graded-index multimode fiber coupler) through the first erbium-doped fiber 104 (EDF-MM-20 / 125-25 step-index multimode erbium-doped fiber), the 80% output end of the fiber coupler 105 (MCMMFC-12-1550-20-L-OM4-10-L-N / FA graded-index multimode fiber coupler) is connected with the input end of the three-ring fiber polarization controller 106 (MCFPC560 three-ring fiber polarization controller), the output end of the three-ring fiber polarization controller 106 (MCFPC560 three-ring fiber polarization controller) is connected with the input end of the polarization-dependent isolator 107 (MCPSI-1550-L-C-S-S2-10-L-FA polarization-dependent isolator), the output end of the polarization-dependent isolator 107 (MCPSI-1550-L-C-S-S2-10-L-FA polarization-dependent isolator) is connected with the input end of the squeezed polarization controller 108 (PLC-003 FPC-100 FPC-200 squeezed polarization controller), the output end of the squeezed polarization controller 108 (PLC-003 FPC-100 FPC-200 squeezed polarization controller) is connected with the input end of the first collimator 109 (M011 collimator), the light pulse is incident to the first mirror 110 (GMH12-005-AU mirror) through the first collimator 109 (M011 collimator), the first mirror 110 (GMH12-005-AU mirror) reflects the light pulse to the first grating 111 (LSFSG-1000-3225-94 grating), the light pulse output by the first grating 111 (LSFSG-1000-3225-94 grating) passes through the first convex lens 112 (GLH12-002-002-NIR convex lens), the liquid crystal spatial light modulator 113 (SLM-256-NIR spatial light modulator), the second convex lens 114 (GLH12-002-002-NIR convex lens),The light pulse is transmitted to the second grating 115 (LSFSG-1000-3225-94 grating), which reflects the light pulse to the second mirror 116 (GMH12-005-AU mirror), and then to the second collimator 117 (M011 collimator). The second collimator 117 (M011 collimator) is connected to the common end of the wavelength division multiplexer 103 (MCFWDM-9855-1-H1 / 20 / 130 / 08D-10-L-N few-mode fiber wavelength division multiplexer). The light pulse is output from the 20% output end of the fiber coupler 105 (MCMMFC-12-1550-20-L-OM4-10-L-N / FA graded index multimode fiber coupler). The seed pulse source outputs high-power pure quartic spatiotemporal mode-locked pulses.

[0033] Example 3 Pretreatment module

[0034] The optical path structure of the pretreatment module 2 is as shown in Figure 3As shown, the light pulse is incident to the third collimator 201 (M011 collimator), and sequentially passes through the first isolator 202 (HOI-005-532 isolator), the first half-wave plate 203 (WPZ2310-248 half-wave plate), and the first filter 204 (HBF-6-1550-D25 filter), and is incident to the third mirror 205 (GMH12-005-AU mirror). The light pulse is reflected by the third mirror 205 (GMH12-005-AU mirror) to the dichroic mirror 209 (GLH31-025-050-SWIR dichroic mirror). The pump light generated by the photodiode 206 (D4F2P22-976 photodiode) passes through the fourth collimator 207 (M011 collimator) and the third convex lens 208 (GLH12-002-002-NIR convex lens), and is combined with the light pulse incident to the dichroic mirror 209 (GLH31-025-050-SWIR dichroic mirror) before. The combined light pulse is incident to the fourth convex lens 210 (GLH12-002-002-NIR convex lens), and sequentially passes through the fifth collimator 211 (M011 collimator), the second erbium-doped fiber 212 (Er80-4 / 125 erbium-doped fiber), the sixth collimator 213 (M011 collimator), and the fifth convex lens 214 (GLH12-002-002-NIR convex lens), and is incident to the fourth mirror 215 (GMH12-005-AU mirror). The fourth mirror 215 (GMH12-005-AU mirror) reflects the light pulse to the fifth mirror 216 (GMH12-005-AU mirror), and the fifth mirror 216 (GMH12-005-AU mirror) reflects the light pulse to the second half-wave plate 217 (WPZ2310-248 half-wave plate). Subsequently, the light pulse sequentially passes through the first quarter-wave plate 218 (WPZ4310-248 quarter-wave plate) and the third half-wave plate 219 (WPZ2310-248 half-wave plate), and is incident to the first polarization beam splitter 220 (QTFBC-1216 polarization beam splitter). The first polarization beam splitter 220 (QTFBC-1216 polarization beam splitter) reflects the main pulse to the first high reflector 222 (HLM020-45-1550 high reflector), and transmits the stray light to the first light block 221 (HC-PSC6030 light block) for absorption. The first high reflector 222 (HLM020-45-1550 high reflector) transmits the main pulse to the third grating 223 (LSFSG-1000-3225-94 grating) and the fourth grating 224 (LSFSG-1000-3225-94 grating) to form a grating pair, and further incident to the first corner reflector 225 (GP16-025 corner reflector).The light pulse is reflected by the first corner reflector 225 (GP16-025 corner reflector) back to the fourth grating 224 (LSFSG-1000-3225-94 grating), passes through the fourth grating 224 (LSFSG-1000-3225-94 grating) and the third grating 223 (LSFSG-1000-3225-94 grating) again, and is finally reflected by the first high-reflectivity mirror 222 (HLM020-45-1550 high-reflectivity mirror) to be output. The pre-processing module 2 adjusts the chirp amount of the light pulse and compresses the width of the light pulse to prevent the amplified light pulse from damaging the optical device.

[0035] Embodiment 4 Energy amplification module

[0036] The optical path structure of the energy amplification module 3 is as shown in Figure 4As shown, the light pulse is incident on the fourth half-wave plate 301 (WPZ2310-248 half-wave plate) to the second polarization beam splitter 302 (QTFBC-1216 polarization beam splitter), and is divided into equal intensity transmitted light and reflected light, wherein the reflected light is reflected by the second high reflector 303 (HLM020-45-1550 high reflector) and the third high reflector 304 (HLM020-45-1550 high reflector), and then transmitted to the third polarization beam splitter 305 (QTFBC-1216 polarization beam splitter); while the transmitted light is directly transmitted to the third polarization beam splitter 305 (QTFBC-1216 polarization beam splitter), and the two beams are combined at the third polarization beam splitter 305 (QTFBC-1216 polarization beam splitter). The combined light pulse passes through the fifth half-wave plate 306 (WPZ2310-248 half-wave plate) and the fourth polarization beam splitter 307 (QTFBC-1216 polarization beam splitter) in turn, and is again divided by the fourth polarization beam splitter 307 (QTFBC-1216 polarization beam splitter) into equal intensity transmitted light and reflected light. The reflected light is reflected by the fourth high reflector 308 (HLM020-45-1550 high reflector) and the fifth high reflector 309 (HLM020-45-1550 high reflector), and then combined with another light pulse transmitted by the fourth polarization beam splitter 307 (QTFBC-1216 polarization beam splitter) at the fifth polarization beam splitter 310 (QTFBC-1216 polarization beam splitter). The combined light pulse is incident on the fiber amplifier 311 (MPA4720-G40-M00-S00 fiber amplifier) for energy amplification. The amplified light pulse is reflected by the sixth mirror 312 (GMH12-005-AU mirror) to the sixth half-wave plate 313 (WPZ2310-248 half-wave plate), and then is incident on the sixth polarization beam splitter 314 (QTFBC-1216 polarization beam splitter) and is divided into two equal intensity and orthogonal polarization pulses. One of the pulses is incident on the seventh mirror 316 (GMH12-005-AU mirror) through the second quarter-wave plate 315 (WPZ4310-248 quarter-wave plate), and then returns to the sixth polarization beam splitter 314 (QTFBC-1216 polarization beam splitter) along the original path, while the other pulse is incident on the eighth mirror 318 (GMH12-005-AU mirror) through the third quarter-wave plate 317 (WPZ4310-248 quarter-wave plate), and also returns to the sixth polarization beam splitter 314 (QTFBC-1216 polarization beam splitter) along the original path, and then the two pulses are combined into one pulse from the sixth polarization beam splitter 314 (QTFBC-1216 polarization beam splitter) to the seventh half-wave plate 319 (WPZ2310-248 half-wave plate).The synthetic pulse is incident to the seventh polarizing beam splitter 320 (QTFBC-1216 polarizing beam splitter) through the seventh half-wave plate 319 (WPZ2310-248 half-wave plate), and is again divided into two pulses of equal intensity and orthogonal polarization. One of the two pulses is incident to the ninth mirror 322 (GMH12-005-AU mirror) through the fourth quarter-wave plate 321 (WPZ4310-248 quarter-wave plate), and then returns to the seventh polarizing beam splitter 320 (QTFBC-1216 polarizing beam splitter) by the original route, while the other pulse is incident to the tenth mirror 324 (GMH12-005-AU mirror) through the fifth quarter-wave plate 323 (WPZ4310-248 quarter-wave plate), and also returns to the seventh polarizing beam splitter 320 (QTFBC-1216 polarizing beam splitter) by the original route, after which the two pulses are combined into one pulse transmitted from the seventh polarizing beam splitter 320 (QTFBC-1216 polarizing beam splitter) to the eighth half-wave plate 325 (WPZ2310-248 half-wave plate). The optical pulse is incident to the eighth polarizing beam splitter 326 (QTFBC-1216 polarizing beam splitter) through the eighth half-wave plate 325 (WPZ2310-248 half-wave plate), and the eighth polarizing beam splitter 326 (QTFBC-1216 polarizing beam splitter) reflects the main pulse to the second filter 328 (204HBF-6-1550-D25 filter) while transmitting the stray light to the second light block 327 (HC-PSC6030 light block) for absorption. The filtered main pulse is reflected to the fifth grating 330 (LSFSG-1000-3225-94 grating) through the sixth high-reflection mirror 329 (HLM020-45-1550 high-reflection mirror), and then is incident to the second corner mirror 332 (GP16-025 corner mirror) after passing through the grating pair composed of the fifth grating 330 (LSFSG-1000-3225-94 grating) and the sixth grating 331 (LSFSG-1000-3225-94 grating). The optical pulse returns to the original route through the second corner mirror 332 (GP16-025 corner mirror), passes through the grating pair again, is received by the sixth high-reflection mirror 329 (HLM020-45-1550 high-reflection mirror) and transmitted to the third filter 333 (204HBF-6-1550-D25 filter), and is finally reflected and output by the eleventh mirror 334 (GMH12-005-AU mirror). The energy amplification module coherently combines and amplifies the pulses.

[0037] Example 5: Spectral Shifting Module

[0038] The optical path structure of the spectral shifting module 4 is as shown in Figure 5As shown, the light pulse is incident to the second isolator 401 (HOI-005-532 isolator), first through the second isolator 401 (HOI-005-532 isolator), the ninth half-wave plate 402 (WPZ2310-248 half-wave plate), the sixth convex lens 403 (GLH12-002-002-NIR convex lens) into the semiconductor optical amplifier 404 (SOA-1550-20-G30 semiconductor optical amplifier) for amplification. The amplified light pulse in turn through the seventh convex lens 405 (GLH12-002-002-NIR convex lens), the first cylindrical lens 406 (GLH15-12x10-025 cylindrical lens), the first prism 407 (GPH12-015 prism), the second prism 408 (GPH12-015 prism), the eighth convex lens 409 (GLH12-002-002-NIR convex lens), the third isolator 410 (HOI-005-532 isolator), the tenth half-wave plate 411 (WPZ2310-248 half-wave plate), and then reflected by the twelfth mirror 412 (GMH12-005-AU mirror) to the first flat mirror 413 (GMH12-025A-AU flat mirror). After the light pulse is transmitted through the first flat mirror 413 (GMH12-025A-AU flat mirror), it is transmitted through the first flat mirror with piezoelectric ceramic 419 (GMH12-025A-AU flat mirror), the first concave mirror 420 (GMH-13 concave mirror), and the LBO crystal 421 (4 mm x 4 mm x 10 mm BBO crystal) to the second concave mirror 422 (GMH-13 concave mirror). The second concave mirror 422 (GMH-13 concave mirror) reflects the fundamental light pulse back to the first flat mirror 413 (GMH12-025A-AU flat mirror) for continuous circulation, while the light pulse reflected by the first flat mirror 413 (GMH12-025A-AU flat mirror) passes through the thirteenth mirror 414 (GMH12-005-AU mirror) and the eleventh half-wave plate 415 (WPZ2310-248 half-wave plate) in turn and is transmitted to the ninth polarization beam splitter 416 (QTFBC-1216 polarization beam splitter), which is divided into two pulses with equal intensity and orthogonal polarization, which are received by the first photodetector 417 (RX25BF photodetector) and the second photodetector 418 (RX25BF photodetector), respectively, for real-time monitoring of the intracavity state. The second concave mirror 422 (GMH-13 concave mirror) transmits the frequency-doubled light to the second cylindrical lens 423 (GLH15-12x10-025 cylindrical lens), which passes through the fourteenth mirror 424 (GMH12-005-AU mirror), the third cylindrical lens 425 (GLH15-12x10-025 cylindrical lens), and the twelfth half-wave plate 426 (WPZ2310-248 half-wave plate) in turn and is transmitted to the second flat mirror 427 (GMH12-025A-AU flat mirror).The light pulse is transmitted through the second plane mirror 427 (GMH12-025A-AU plane mirror), the second piezoelectric ceramic plane mirror 433 (GMH12-025A-AU plane mirror), the third concave mirror 434 (GMH-13 concave mirror), the KBBF crystal 435 (1.5 mm thick KBBF crystal), and then transmitted to the fourth concave mirror 436 (GMH-13 concave mirror). The fourth concave mirror 436 (GMH-13 concave mirror) reflects the fundamental frequency light pulse back to the second plane mirror 427 (GMH12-025A-AU plane mirror) for continuous circulation, while the light pulse reflected by the second plane mirror 427 (GMH12-025A-AU plane mirror) is transmitted through the fifteenth mirror 428 (GMH12-005-AU mirror), the thirteenth half wave plate 429 (WPZ2310-248 half wave plate) to the tenth polarization beam splitter 430 (QTFBC-1216 polarization beam splitter) in turn, and is divided into two pulses with equal intensity and orthogonal polarization, which are received by the third photodetector 431 (RX25BF photodetector) and the fourth photodetector 432 (RX25BF photodetector) respectively, for real-time monitoring of the cavity state. Finally, the spectral shift is realized in the KBBF crystal 435 (1.5 mm thick KBBF crystal), and ultraviolet laser output is generated.

[0039] Embodiment 6 Working principle of the present application

[0040] The working principle of the present application is illustrated in combination with the above embodiments and the accompanying drawings.

[0041] In the seed pulse source 1, the first erbium-doped fiber 104 is a step-index multimode fiber, and the fiber coupler 105 is a graded-index multimode fiber, both of which belong to multimode fibers, have larger core diameters and mode areas, and can withstand higher nonlinear effects to realize high-energy temporal-spatial mode-locked laser output. The programmable pulse shaping structure composed of the first grating 111, the first convex lens 112, the liquid crystal spatial light modulator 113, the second convex lens 114, and the second grating 115 can realize in-cavity high-order dispersion management, so that the temporal-spatial mode-locked fiber laser outputs high-energy pure quartic temporal-spatial mode-locked pulses without being limited by the soliton area theory. The pre-processing module 2 uses a grating to adjust the pulse chirp and compress the pulse spectral width, preventing the amplified pulse from damaging the amplifier. The energy amplification module 3 uses a coherent synthesis amplification structure for effective power amplification, and further compresses the pulse width using a grating to obtain ultrashort pulse output. The spectral shift module performs nonlinear frequency conversion through an LBO crystal and a KBBF crystal to finally realize high-power ultrashort ultraviolet pulse output.

[0042] Embodiment 7 Results of the present application

[0043] Figure 6The beam profile of the output pulse from the seed pulse source 1 is shown, with its non-Gaussian distribution reflecting the typical output characteristics of the spatiotemporal mode-locked pulse. Figure 7 The spectral profile of the pulse is shown, with the center wavelength at 1550 nm. Figure 8 The time-domain waveform of the pulse is shown, with the measured peak power of 4.3 kW. The slight oscillation tailing observed in the time-domain profile confirms that the pulse is a pure quartic spatiotemporal soliton pulse.

[0044] Figure 9 The beam profile of the final output pulse is shown, with only slight changes in shape compared to Figure 6 compared to the beam profile of the seed pulse, indicating that the beam quality has not been degraded after the pre-processing module 2, the energy amplification module 3, and the spectral shifting module 4, and the spatiotemporal mode-locked characteristics are maintained. Figure 10 The spectral profile of the final output pulse is shown, with the center wavelength shifted to 387.5 nm, demonstrating the successful spectral shifting and the achievement of the ultrashort ultraviolet pulse output. Figure 11 The corresponding time-domain waveform shows that the output pulse intensity is significantly improved, with a peak power of 36.2 kW, achieving effective amplification of the power. At the same time, the pulse still presents oscillation tailing, further confirming its pure quartic soliton characteristics.

[0045] In summary, the seed pulse source 1 can generate a pure quartic spatiotemporal soliton pulse with excellent beam quality. After the pre-processing module 2, the energy amplification module 3, and the spectral shifting module 4, the output power is significantly improved while maintaining high beam quality and pure quartic spatiotemporal mode-locked characteristics. The spectrum is successfully shifted to the ultraviolet band, and finally, a high-power ultrashort ultraviolet pulse output is obtained.

Claims

1. A high-energy pulse laser system based on spatiotemporal mode locking, comprising a seed pulse source (1) connected to an input end of a preprocessing module (2), an output end of the preprocessing module (2) connected to an input end of an energy amplification module (3), and an output end of the energy amplification module (3) connected to an input end of a spectrum shift module (4); the seed pulse source (1) uses a step-index multimode fiber as a gain medium and a graded-index multimode fiber as a passive fiber; a section of a few-mode fiber with a core diameter of 20 µm is fused to the graded-index multimode fiber with a core diameter of 50 µm to realize spatial filtering; the seed pulse source (1) is internally integrated with a programmable pulse shaping structure composed of a pair of diffraction gratings, a pair of lenses, and a liquid crystal spatial light modulator; the energy amplification module (3) comprises a pulse splitter and a pulse combiner based on beam splitting delay, both of which have the same optical configuration and are composed of two polarization beam splitters and two high-reflectivity mirrors; the spectrum shift module (4) comprises two nonlinear crystals and a tapered amplifier with a tapered cross section capable of maintaining high beam quality, wherein the two nonlinear crystals are a LBO biaxial crystal with the characteristics of wide light transmission range, high damage threshold, and high conversion efficiency, and a KBBF negative uniaxial crystal achieving phase matching through prism coupling; the seed pulse source (1) comprises a pump source (101) connected to an input end of a mode field adapter (102), an output end of the mode field adapter (102) connected to a 980 nm end of a wavelength division multiplexer (103), a 1550 nm end of the wavelength division multiplexer (103) connected to an input end of a fiber coupler (105) through a first erbium-doped fiber (104), a 80% output end of the fiber coupler (105) connected to an input end of a three-ring fiber polarization controller (106), an output end of the three-ring fiber polarization controller (106) connected to an input end of a polarization-dependent isolator (107), an output end of the polarization-dependent isolator (107) connected to an input end of an extrusion-type polarization controller (108), an output end of the extrusion-type polarization controller (108) connected to an input end of a first collimator (109), and light pulses incident on a first mirror (110) through the first collimator (109), the first mirror (110) reflecting the light pulses to a first grating (111), the light pulses output by the first grating (111) transmitted to a second grating (115) through a first convex lens (112), a liquid crystal spatial light modulator (113), and a second convex lens (114), the second grating (115) reflecting the light pulses to a second mirror (116), and then to a second collimator (117); the second collimator (117) is connected to a common end of the wavelength division multiplexer (103); and light pulses are output from a 20% output end of the fiber coupler (105). The spectrum shift module (4) has the following optical path structure: the light pulse is incident to the second isolator (401), first passes through the second isolator (401), the ninth half-wave plate (402), the sixth convex lens (403) into the semiconductor optical amplifier (404) for amplification, and then the amplified light pulse passes through the seventh convex lens (405), the first cylindrical lens (406), the first prism (407), the second prism (408), the eighth convex lens (409), the third isolator (410), the tenth half-wave plate (411) in turn, and is reflected to the first plane mirror (413) by the twelfth mirror (412). The light pulse is transmitted through the first plane mirror (413), and then is transmitted to the second concave mirror (422) through the first piezoelectric ceramic plane mirror (419), the first concave mirror (420) and the LBO crystal (421). The second concave mirror (422) reflects the fundamental frequency light pulse back to the first plane mirror (413) for continuous circulation, and the light pulse reflected by the first plane mirror (413) passes through the thirteenth mirror (414) and the eleventh half-wave plate (415) in turn and is transmitted to the ninth polarization beam splitter (416), and is divided into two pulses with equal intensity and orthogonal polarization, which are received by the first photodetector (417) and the second photodetector (418) respectively, for real-time monitoring of the cavity state. The second concave mirror (422) transmits the frequency-doubled light to the second cylindrical lens (423), which passes through the fourteenth mirror (424), the third cylindrical lens (425) and the twelfth half-wave plate (426) in turn and is transmitted to the second plane mirror (427). The light pulse is transmitted through the second plane mirror (427), and then is transmitted to the fourth concave mirror (436) through the second piezoelectric ceramic plane mirror (433), the third concave mirror (434) and the KBBF crystal (435). The fourth concave mirror (436) reflects the fundamental frequency light pulse back to the second plane mirror (427) for continuous circulation, and the light pulse reflected by the second plane mirror (427) passes through the fifteenth mirror (428) and the thirteenth half-wave plate (429) in turn and is transmitted to the tenth polarization beam splitter (430), and is divided into two pulses with equal intensity and orthogonal polarization, which are received by the third photodetector (431) and the fourth photodetector (432) respectively, for real-time monitoring of the cavity state. Finally, the spectrum shift is realized in the KBBF crystal (435), and ultraviolet laser output is generated.

2. The high-energy pulsed laser system based on spatiotemporal mode-locking according to claim 1, characterized in that, The preprocessing module (2) has the following optical path structure: the light pulse is incident to the third collimator (201), sequentially passes through the first isolator (202), the first half-wave plate (203), the first filter (204), and is incident to the third mirror (205), the light pulse is reflected by the third mirror (205) to the dichroic mirror (209); the pump light generated by the photodiode (206) passes through the fourth collimator (207) and the third convex lens (208), and is combined with the light pulse incident to the dichroic mirror (209) before; the combined light pulse is incident to the fourth convex lens (210), sequentially passes through the fifth collimator (211), the second erbium-doped fiber (212), the sixth collimator (213), and the fifth convex lens (214), and is incident to the fourth mirror (215), and is reflected by the fourth mirror (215) to the fifth mirror (216), and is reflected to the second half-wave plate (217); then, the light pulse sequentially passes through the first quarter-wave plate (218) and the third half-wave plate (219), and is incident to the first polarization beam splitter (220), the first polarization beam splitter (220) reflects the main pulse to the first high-reflectivity mirror (222), and transmits the stray light to the first light block (221) for absorption; the first high-reflectivity mirror (222) transmits the main pulse to the grating pair composed of the third grating (223) and the fourth grating (224), and further is incident to the first angle mirror (225); the light pulse is reflected by the first angle mirror (225) back to the fourth grating (224), passes through the fourth grating (224) and the third grating (223) again, and is finally reflected by the first high-reflectivity mirror (222) and output.

3. The high-energy pulsed laser system based on spatiotemporal mode-locking according to claim 1, wherein, The energy amplification module (3) has the following optical path structure: the light pulse is incident to the second polarizing beam splitter (302) through the fourth half wave plate (301), and is divided into transmitted light and reflected light with equal intensity, wherein the reflected light is transmitted to the third polarizing beam splitter (305) after being reflected by the second high reflection mirror (303) and the third high reflection mirror (304); and the transmitted light is directly transmitted to the third polarizing beam splitter (305), and the two beams of light are combined at the third polarizing beam splitter (305); the combined light pulse passes through the fifth half wave plate (306) and the fourth polarizing beam splitter (307) in turn, and is again divided by the fourth polarizing beam splitter (307) into transmitted light and reflected light with equal intensity, wherein the reflected light is reflected by the fourth high reflection mirror (308) and the fifth high reflection mirror (309), and is combined with another light pulse transmitted by the fourth polarizing beam splitter (307) at the fifth polarizing beam splitter (310); the combined light pulse is incident to the fiber amplifier (311) for energy amplification, and the amplified light pulse is reflected by the sixth reflection mirror (312) to the sixth half wave plate (313), and then is incident to the sixth polarizing beam splitter (314) and is divided into two beams of pulses with equal intensity and orthogonal polarization, wherein one of the two beams of pulses is incident to the seventh reflection mirror (316) through the second quarter wave plate (315), and then returns to the sixth polarizing beam splitter (314) in the original path, while the other beam of pulse is incident to the eighth reflection mirror (318) through the third quarter wave plate (317), and also returns to the sixth polarizing beam splitter (314) in the original path, and then the two beams of pulses are combined into one beam from the sixth polarizing beam splitter (314) to the seventh half wave plate (319), and the combined pulse is incident to the seventh polarizing beam splitter (320) through the seventh half wave plate (319), and is again divided into two beams of pulses with equal intensity and orthogonal polarization, wherein one of the two beams of pulses is incident to the ninth reflection mirror (322) through the fourth quarter wave plate (321), and then returns to the seventh polarizing beam splitter (320) in the original path, while the other beam of pulse is incident to the tenth reflection mirror (324) through the fifth quarter wave plate (323), and also returns to the seventh polarizing beam splitter (320) in the original path, and then the two beams of pulses are combined into one beam from the seventh polarizing beam splitter (320) to the eighth half wave plate (325), and the light pulse is incident to the eighth polarizing beam splitter (326) through the eighth half wave plate (325), and the eighth polarizing beam splitter (326) reflects the main pulse to the second filter (328), and transmits the stray light to the second light block (327) for absorption, and the filtered main pulse is reflected by the sixth high reflection mirror (329) to the fifth grating (330), and then is incident to the second corner reflection mirror (332) after passing through the grating pair composed of the fifth grating (330) and the sixth grating (331); the light pulse returns to the original path through the second corner reflection mirror (332), passes through the grating pair again, is received by the sixth high reflection mirror (329) and transmitted to the third filter (333), and is finally reflected and output by the eleventh reflection mirror (334).

Images