A novel scheme to suppress both stimulated Brillouin scattering(SBS) and stimulated Raman scattering(SRS) by combining an alternating frequency(AF) laser and a transverse magnetic field is proposed. The AF laser allow...A novel scheme to suppress both stimulated Brillouin scattering(SBS) and stimulated Raman scattering(SRS) by combining an alternating frequency(AF) laser and a transverse magnetic field is proposed. The AF laser allows the laser frequency to change discretely and alternately over time. The suppression of SBS is significant as long as the AF difference is greater than the linear growth rate of SBS or the alternating time of the laser frequency is shorter than the linear growth time of SBS. However, the AF laser proves ineffective in suppressing SRS, which usually has a much higher linear growth rate than SBS. To remedy that, a transverse magnetic field is included to suppress the SRS instability. The electrons trapped in the electron plasma waves(EPWs) of SRS can be accelerated by the surfatron mechanism in a transverse magnetic field and eventually detrapped. While continuously extracting energy from EPWs, the EPWs are dissipated and the kinetic inflation of SRS is suppressed. The one-dimensional particle-in-cell simulation results show that both SBS and SRS can be effectively suppressed by combining the AF laser with a transverse magnetic field with tens of Tesla. The total reflectivity can be dramatically reduced by more than one order of magnitude. These results provide a potential reference for controlling SBS and SRS under the related parameters of inertial confinement fusion.展开更多
Transverse stimulated Raman scattering(TSRS)in potassium dihydrogen phosphate(KDP)and deuterated potassium dihydrogen phosphate(DKDP)plates for large-aperture,inertial confinement fusion(ICF)-class laser systems is a ...Transverse stimulated Raman scattering(TSRS)in potassium dihydrogen phosphate(KDP)and deuterated potassium dihydrogen phosphate(DKDP)plates for large-aperture,inertial confinement fusion(ICF)-class laser systems is a well-recognized limitation giving rise to parasitic energy conversion and laser-induced damage.The onset of TSRS is manifested in plates exposed to the ultraviolet section of the beam.TSRS amplification is a coherent process that grows exponentially and is distributed nonuniformly in the crystal and at the crystal surfaces.To understand the growth and spatial distribution of TSRS energy in various configurations,a modeling approach has been developed to simulate the operational conditions relevant to ICF-class laser systems.Specific aspects explored in this work include(i)the behavior of TSRS in large-aperture crystal plates suitable for third-harmonic generation and use as wave plates for polarization control in current-generation ICF-class laser system configurations;(ii)methods,and their limitations,of TSRS suppression and(iii)optimal geometries to guide future designs.展开更多
Transverse stimulated Raman scattering （TSRS） gain coefficient in a large aperture 65% deu terated potassium dihydrogen phosphate （DKDP） is measured at 351 nm. The measurement involves the use of an optical fiber ...Transverse stimulated Raman scattering （TSRS） gain coefficient in a large aperture 65% deu terated potassium dihydrogen phosphate （DKDP） is measured at 351 nm. The measurement involves the use of an optical fiber sensor system to detect Raman scattering light in the DKDP crystal. A Raman scattering gain coefficient of 0. 109 cm/GW is obtained and will be used to set upper limit of the DKDP crystals in our laser fa cility to avoid the TSRS induced energy loss and laser damage. The effect of bulk damage on growth behavior of TSRS is also examined and it is found that bulk damage has little impact on the TSRS growth. Thus the influ ence of bulk damage on the measurement of TSRS gain coefficient can be ignored.展开更多
Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a c...Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a constant cladding and tapered core(CCTC)along its axis direction.The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering(SRS)threshold and suppress higher-order mode resonance in the laser cavity.The CCTC YDF was fabricated successfully with a modified chemical vapor deposition(MCVD)method combined with solution doping technology,which has a cladding diameter of 400µm and a varying core with a diameter of~24μm at both ends and~31μm in the middle.To test the performance of the CCTC fiber during high-power operation,an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally.As a result,a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%,although the TMI effect was observed at an output power of~3.12 kW.The measured beam quality(M^(2)factor)was~1.7,and no sign of the Raman component was observed in the spectrum.We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects,and further power scaling is promising by optimizing the structure of the YDF.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11975059 and 12005021)。
文摘A novel scheme to suppress both stimulated Brillouin scattering(SBS) and stimulated Raman scattering(SRS) by combining an alternating frequency(AF) laser and a transverse magnetic field is proposed. The AF laser allows the laser frequency to change discretely and alternately over time. The suppression of SBS is significant as long as the AF difference is greater than the linear growth rate of SBS or the alternating time of the laser frequency is shorter than the linear growth time of SBS. However, the AF laser proves ineffective in suppressing SRS, which usually has a much higher linear growth rate than SBS. To remedy that, a transverse magnetic field is included to suppress the SRS instability. The electrons trapped in the electron plasma waves(EPWs) of SRS can be accelerated by the surfatron mechanism in a transverse magnetic field and eventually detrapped. While continuously extracting energy from EPWs, the EPWs are dissipated and the kinetic inflation of SRS is suppressed. The one-dimensional particle-in-cell simulation results show that both SBS and SRS can be effectively suppressed by combining the AF laser with a transverse magnetic field with tens of Tesla. The total reflectivity can be dramatically reduced by more than one order of magnitude. These results provide a potential reference for controlling SBS and SRS under the related parameters of inertial confinement fusion.
基金This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856,the University of Rochester and the New York State Energy Research and Development Authority。
文摘Transverse stimulated Raman scattering(TSRS)in potassium dihydrogen phosphate(KDP)and deuterated potassium dihydrogen phosphate(DKDP)plates for large-aperture,inertial confinement fusion(ICF)-class laser systems is a well-recognized limitation giving rise to parasitic energy conversion and laser-induced damage.The onset of TSRS is manifested in plates exposed to the ultraviolet section of the beam.TSRS amplification is a coherent process that grows exponentially and is distributed nonuniformly in the crystal and at the crystal surfaces.To understand the growth and spatial distribution of TSRS energy in various configurations,a modeling approach has been developed to simulate the operational conditions relevant to ICF-class laser systems.Specific aspects explored in this work include(i)the behavior of TSRS in large-aperture crystal plates suitable for third-harmonic generation and use as wave plates for polarization control in current-generation ICF-class laser system configurations;(ii)methods,and their limitations,of TSRS suppression and(iii)optimal geometries to guide future designs.
文摘Transverse stimulated Raman scattering （TSRS） gain coefficient in a large aperture 65% deu terated potassium dihydrogen phosphate （DKDP） is measured at 351 nm. The measurement involves the use of an optical fiber sensor system to detect Raman scattering light in the DKDP crystal. A Raman scattering gain coefficient of 0. 109 cm/GW is obtained and will be used to set upper limit of the DKDP crystals in our laser fa cility to avoid the TSRS induced energy loss and laser damage. The effect of bulk damage on growth behavior of TSRS is also examined and it is found that bulk damage has little impact on the TSRS growth. Thus the influ ence of bulk damage on the measurement of TSRS gain coefficient can be ignored.
基金the National Natural Science Foundation of China(Nos.61735007 and 61705266).
文摘Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a constant cladding and tapered core(CCTC)along its axis direction.The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering(SRS)threshold and suppress higher-order mode resonance in the laser cavity.The CCTC YDF was fabricated successfully with a modified chemical vapor deposition(MCVD)method combined with solution doping technology,which has a cladding diameter of 400µm and a varying core with a diameter of~24μm at both ends and~31μm in the middle.To test the performance of the CCTC fiber during high-power operation,an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally.As a result,a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%,although the TMI effect was observed at an output power of~3.12 kW.The measured beam quality(M^(2)factor)was~1.7,and no sign of the Raman component was observed in the spectrum.We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects,and further power scaling is promising by optimizing the structure of the YDF.
