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High-power mode-programmable orbital angular momentum beam emitter with an internally sensed optical phased array

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Chinese Optics Letters 2024年第2期22卷 120-127页

作者：龙金虎邓宇高志强常洪祥常琦马阎星吴坚粟荣涛马鹏飞周朴 College of Advanced Interdisciplinary Studies National University of Defense TechnologyChangsha 410073China Nanhu laser Laboratory National University of Defense TechnologyChangsha 410073China Hunan Provincial Key Laboratory of High Energy laser technology National University of Defense TechnologyChangsha 410073China

The high-power mode-programmable orbital angular momentum(OAM)beam has attracted significant attention in a wide range of applications,such as long-distance optical communication,nonlinear frequency conversion,and beam *** beam combining(CBC)of an optical phased array(OPA)can offer a promising solution for both generating the high-power OAM beam and rapidly switching the OAM ***,achieving real-time phase noise locking and formation of desired phase structures in a high-power CBC system faces significant ***,an internal phase-sensing technique was utilized to generate the high-power OAM beam,which effectively mitigated thermal effects and eliminated the need for large optical *** OPA with six elements was employed for experimental *** first effective generation of over 1.5 kW mode-programmable OAM beam in a continuous-wave domain was ***,the results demonstrated that the generated OAM beam could be modulated with multiple *** topological charge can be switched in real time from-1 ***,this OAM beam emitter could function as an OAM beam copier by easily transforming a single OAM beam into an OAM beam *** importantly,a comprehensive analysis was conducted on power scaling,mode switching speed,and expansion of OAM ***,the system’s compact design enabled it to function as a packageable OAM beam *** to the advantages of having high power and programmable modes with multiple dimension modulation in phase structures and intensity distribution,this work can pave the way for producing high-power structured light beams and advancing their applications.

关键词： orbital angular momentum optical vortex optical phased array coherent beam combining

Color coded metadevices toward programmed terahertz switching

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Light(Science & Applications) 2024年第7期13卷 1383-1392页

作者： Weibao He Xiang’ai Cheng Siyang Hu Ziheng Ren Zhongyi Yu Shun Wan Yuze Hu Tian Jiang College of Advanced Interdisciplinary Studies National University of Defense TechnologyChangshaChina. Nanhu laser Laboratory National University of Defense TechnologyChangshaChina. Hunan Provincial Key Laboratory of High Energy laser technology National University of Defense TechnologyChangshaChina. Institute for Quantum Science and technology College of ScienceNational University of Defense TechnologyChangshaChina

Terahertz modulators play a critical role in high-speed wireless communication,non-destructive imaging,and so on,which have attracted a large amount of research ***,all-optical terahertz modulation,an ultrafast dynamical control approach,remains to be limited in terms of encoding and *** we experimentally demonstrated an optical-programmed terahertz switching realized by combining optical metasurfaces with the terahertz metasurface,resulting in 2-bit dual-channel terahertz *** terahertz metasurface,made up of semiconductor islands and artificial microstructures,enables effective all-optical programming by providing multiple frequency channels with ultrafast modulation at the nanosecond ***,optical metasurfaces covered in terahertz metasurface alter the spatial light field distribution to obtain color *** to the time-domain coupled mode theory analysis,the energy dissipation modes in terahertz metasurface can be independently controlled by color excitation,which explains the principle of 2-bit encoding *** work establishes a platform for all-optical programmed terahertz metadevices and may further advance the application of composite metasurface in terahertz manipulation.

关键词： terahertz surface excitation

In-situ analysis of laser-induced breakdown spectra for online monitoring of femtosecond laser machining of sapphire

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Science China(Technological Sciences) 2024年第1期67卷 73-82页

作者： SHANGGUAN ShiYong ZHANG JianGuo LI ZhanZhu SHI Wei WANG WenKe QI DongFeng ZHENG HongYu center for Advanced laser Manufacturing(CALM) Shandong University of TechnologyZibo 255000China

laser-induced breakdown spectroscopy(LIBS)is widely used for elemental ***,its application for monitoring and analyzing a laser machining process by examining the changes in spectral information warrants further *** this study,we investigate the effect of laser parameters on the spectra,variations in the time-resolved plasma emission spectra,and the relationship between the morphology of craters and plasma plume evolution during the femtosecond(fs)laser ablation of *** Boltzmann plot method and Stark’s broadening model are employed to estimate the temporal temperature and electron density of the plasma plume,revealing the process of plasma *** study aims to demonstrate the feasibility of LIBS for online monitoring of laser processing through experimental data and theoretical explanations.

关键词： laser-induced breakdown spectroscopy plasma plume online monitoring sapphire

Coherent beam combining of two all‑PM thulium‑doped fiber chirped pulse amplifiers

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Frontiers of Optoelectronics 2024年第2期17卷 33-42页

作者： Bo Ren Hongxiang Chang Can Li Tao Wang Kaikai Jin Jiayi Zhang Kun Guo Rongtao Su Jinyong Leng Pu Zhou College of Advanced Interdisciplinary Studies National University of Defense TechnologyChangsha 410073China Nanhu laser Laboratory National University of Defense TechnologyChangsha 410073China Hunan Provincial Key Laboratory of High Energy laser technology National University of Defense TechnologyChangsha 410073China

In this paper,we report a coherent beam combining(CBC)system that involves two thulium-doped all-polarization maintaining(PM)fiber chirped pulse *** phase-locking the two channels via a fiber stretcher by using the stochastic parallel gradient descent(SPGD)algorithm,a maximum average power of 265 W is obtained,with a CBC efficiency of 81%and a residual phase error of λ/*** de-chirping by a pair of diffraction gratings,the duration of the combined laser pulse is compressed to 690 *** into account the compression efficiency of 90%and the main peak energy proportion of 91%,the corresponding peak power is calculated to be 4 *** laser noise characteristics before and after CBC are examined,and the results indicate that the CBC would degrade the low frequency relative intensity noise(RIN),of which the integration is 1.74%in[100 Hz,2 MHz]at the maximum combined output *** addition,the effects of the nonlinear spectrum broadening during chirped pulse amplification on the CBC efficiency are also investigated,showing that a higher extent of pulse stretching is effective in alleviating the spectrum broadening and realizing a higher output power with decent combining efficiency.

关键词： Coherent beam combining Thulium-doped fiber laser High-average power Chirped pulse amplifier

5 kW-level single-mode fiber amplifier based on low-numerical-aperture fiber

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Chinese Optics Letters 2024年第4期22卷 71-76页

作者：陈益沙叶云黄良金杨欢吴函烁闫志平潘志勇王小林王泽锋周朴 College of Advanced Interdisciplinary Studies National University of Defense TechnologyChangsha 410073China Nanhu laser Laboratory National University of Defense TechnologyChangsha 410073China Hunan Provincial Key Laboratory of High Energy laser technology National University of Defense TechnologyChangsha 410073China

A low-numerical-aperture(NA)concept enables large-mode-area fiber with better single-mode operation ability,which is beneficial for transverse mode instability and nonlinear effects *** this contribution,we reported a high-power fiber amplifier based on a piece of self-developed large-mode-area low-NA fiber with a core NA of 0.049 and a core/inner cladding diameter of 25/400μ*** influence of the pump wavelength and fiber length on the power scaling potential of the fiber amplifier is systematically *** a result,an output of 4.80 kW and a beam quality factor of~1.33 were finally obtained,which is the highest output power ever reported in a fiber amplifier exploiting the low-NA *** results reveal that low-NA fibers have superiority in power scaling and beam quality maintenance at high power levels.

关键词： high power fiber lasers ytterbium-doped fiber low-numerical-aperture fiber mode instability

Internal phase control of fiber laser array based on photodetector array

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Chinese Physics B 2024年第7期33卷 320-326页

作者：靳凯凯龙金虎常洪祥粟荣涛张嘉怡陈思雨马阎星周朴 College of Advanced Interdisciplinary Studies National University of Defense TechnologyChangsha 410073China Nanhu laser Laboratory National University of Defense TechnologyChangsha 410073China Hunan Provincial Key Laboratory of High Energy laser technology National University of Defense TechnologyChangsha 410073China

Coherent beam combining(CBC) of fiber laser array is a promising technique to realize high output power while maintaining near diffraction-limited beam quality. To implement CBC, an appropriate phase control feedback structure should be established to realize phase-locking. In this paper, an innovative internal active phase control CBC fiber laser array based on photodetector array is proposed. The dynamic phase noises of the laser amplifiers are compensated before being emitted into free space. And the static phase difference compensation of emitting laser array is realized by interference measurement based on photodetector array. The principle of the technique is illustrated and corresponding simulations are carried out, and a CBC system with four laser channels is built to verify the technique. When the phase controllers are turned on, the phase deviation of the laser array is less than λ/20, and ~ 95% fringe contrast of the irradiation distribution is obtained. The technique proposed in this paper could provide a reference for the system design of a massive high-power CBC system.

关键词： fiber laser laser array coherent beam combining internal phase control

High power tunable Raman fiber laser at 1.2μm waveband

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Frontiers of Optoelectronics 2024年第1期17卷 1-8页

作者： Yang Zhang Jiangming Xu Junrui Liang Jun Ye Sicheng Li Xiaoya Ma Zhiyong Pan Jinyong Leng Pu Zhou College of Advanced Interdisciplinary Studies National University of Defense TechnologyChangsha 410073China Nanhu laser Laboratory National University of Defense TechnologyChangsha 410073China Hunan Provincial Key Laboratory of High Energy laser technology National University of Defense TechnologyChangsha 410073China

Development of a high power fiber laser at special waveband,which is difficult to achieve by conventional rare-earth-doped fibers,is a significant *** of the most common methods for achieving lasing at special wavelength is Raman ***-doped fiber(PDF),due to the phosphorus-related large frequency shift Raman peak at 40 THz,is a great choice for large frequency shift Raman ***,by adopting 150 m large mode area triple-clad PDF as Raman gain medium,and a novel wavelength-selective feedback mechanism to suppress the silica-related Raman emission,we build a high power cladding-pumped Raman fiber laser at 1.2μm waveband.A Raman signal with power up to 735.8 W at 1252.7 nm is *** the best of our knowledge,this is the highest output power ever reported for fiber lasers at 1.2μm ***,by tuning the wavelength of the pump source,a tunable Raman output of more than 450 W over a wavelength range of 1240.6–1252.7 nm is *** work proves PDF’s advantage in high power large frequency shift Raman conversion with a cladding pump scheme,thus providing a good solution for a high power laser source at special waveband.

关键词： Phosphosilicate fiber Raman fiber laser 1.2μm waveband Wavelength tunable

High power cladding-pumped low quantum defect Raman fiber amplifier

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Photonics Research 2024年第5期12卷 995-1003页

作者： YANG ZHANG JIANGMING Xu JUNRUI LIANG SICHENG LI JUN YE XIAOYA MA TIANFU YAO ZHIYONG PAN JINYONG LENG PU ZHOU College of Advanced Interdisciplinary Studies National University of Defense TechnologyChangsha 410073China Nanhu laser Laboratory National University of Defense TechnologyChangsha 410073China Hunan Provincial Key Laboratory of High Energy laser technology National University of Defense TechnologyChangsha 410073China

Heat generated by the quantum defect(QD)in optically pumped lasers can result in detrimental effects such as mode instability,frequency noise,and even catastrophic ***,we demonstrated that boson-peakbased Raman fiber lasers have great potential in low QD laser *** their power scalability and heat load characteristics have yet to be ***,we demonstrate a boson-peak-based Raman fiber amplifier(RFA)with 815 W output power and a QD of 1.3%.The low heat generation characteristics of this low QD RFA are *** experimental and simulation results show that at this power level,the heat load of the low QD RFA is significantly lower than that of the conventional RFA with a QD of 4.8%.Thanks to its low heat generation characteristics,the proposed phosphosilicate-fiber-based low QD RFA provides an effective solution for the intractable thermal issue in optically pumped lasers,which is of significance in reducing the laser’s noise,improving the laser’s stability and safety,and solving the challenge of heat removing.

关键词： pumped fiber amplifier

Recent progress of parameter-adjustable high-power photonic microwave generation based on wide-bandgap photoconductive semiconductors

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Chinese Optics Letters 2024年第1期22卷 113-122页

作者：荀涛牛昕玥王朗宁张斌姚金妹易木俣杨汉武侯静刘金亮张建徳 College of Advanced Interdisciplinary Studies National University of Defense TechnologyChangsha 410073China Nanhu laser Laboratory National University of Defense TechnologyChangsha 410073China

Radio frequency/microwave-directed energy sources using wide bandgap SiC photoconductive semiconductors have attracted much attention due to their unique advantages of high-power output and multi-parameter adjustable *** the past several years,benefitting from the sustainable innovations in laser technology and the significant progress in materials technology,megawatt-class output power electrical pulses with a flexible frequency in the P and L microwave wavebands have been achieved by photoconductive semiconductor ***,we mainly summarize and review the recent progress of the high-power photonic microwave generation based on the SiC photoconductive semiconductor devices in the linear modulation mode,including the mechanism,system architecture,critical technology,and experimental demonstration of the proposed high-power photonic microwave *** outlooks and challenges for the future of multi-channel power synthesis development of higher power photonic microwave using wide bandgap photoconductors are also discussed.

关键词： high-power photonic microwave wide bandgap photoconductive semiconductor devices linear modulation multi-parameter adjustable microwave generation multi-channel power synthesis