We study a femtosecond Ti：sapphire laser pumped optical parametric amplifier （OPA） at 1053nm. The OPA Generates stable signal pulses with duration smaller than l OOfs, wavelength drift smaller than 0.5 nm, and puls...We study a femtosecond Ti：sapphire laser pumped optical parametric amplifier （OPA） at 1053nm. The OPA Generates stable signal pulses with duration smaller than l OOfs, wavelength drift smaller than 0.5 nm, and pulseto-pulse fluctuation of about ±4%, by employinG an external seeder. In a terawatt laser pumped large-aperture LiNbOa OPA, pulse energy at signal has been scaled up to 4mJ. This m J-class femtosecond OPA at 1053nm presents a feasible alternative to optical parametric chirped-pulse amplification, and is ready to be applied to petawatt lasers.展开更多
Partially deuterated KDP is an ideal nonlinear crystal for second-harmonic generation （SHG） of femtosecond lasers at 1 μm, which features with vanished group-velocity mismatch at its retracing point of phase-matchi...Partially deuterated KDP is an ideal nonlinear crystal for second-harmonic generation （SHG） of femtosecond lasers at 1 μm, which features with vanished group-velocity mismatch at its retracing point of phase-matching. We numerically investigate the characteristics of SHG with femtosecond lasers in a partially deuterated KDP, which shows that group-velocity dispersion plays an important role. This spectrally non-critical phase-matching configuration can support both high efficiency and large acceptance bandwidth.展开更多
We have explicitly identified coloured conical emission （CCE） and noncollinear optical parametric generation （OPC） by spectrum characterizations. With an experimental setup providing different pump pulse durations...We have explicitly identified coloured conical emission （CCE） and noncollinear optical parametric generation （OPC） by spectrum characterizations. With an experimental setup providing different pump pulse durations, CCE and noncollinear OPG are observed both alternatively and simultaneously. Comparisons between CCE and noncollinear OPC are studied. Accumulation behaviour of modulational instabilities is observed in our two-crystal cascaded configuration, which results in enhancement or depression of the CCE formation.展开更多
Cascaded nonlinear phase shifts may be imposed on the interacting waves during second-harmonic generation （SHG） in a quasi-Phase-matched （QPM） structure, whieh are severe in high-intensity regime and may result in...Cascaded nonlinear phase shifts may be imposed on the interacting waves during second-harmonic generation （SHG） in a quasi-Phase-matched （QPM） structure, whieh are severe in high-intensity regime and may result in lower conversion efficiency. We propose a configuration of QPM structure with reduced domain-length, which may depress the nonlinear phase shifts to some extent and lead to an improvement on the conversion efficiency. The numerical analyses on the conversion efficiency as well as the relative phase angle are discussed in detail for better understanding of the SHG process.展开更多
We show analytically that in phase-mismatched second-harmonic generation, an effective diffraction is induced at the second-harmonic （SH） frequency. Numerical simulation results agree with the analytical predictions...We show analytically that in phase-mismatched second-harmonic generation, an effective diffraction is induced at the second-harmonic （SH） frequency. Numerical simulation results agree with the analytical predictions. Compared to the case of linear propagation, the effect of the overall diffraction at the SH frequency becomes doubled due to the induced diffraction, which causes an interesting result that the SH beam width will be larger than that of the fundamental field.展开更多
Scattering-enhanced femtosecond optical parametric generation （OPG） has been observed and studied in detail, which may decrease the pump threshold of OPGs dramatically and may make OPGs reliable. The experimental de...Scattering-enhanced femtosecond optical parametric generation （OPG） has been observed and studied in detail, which may decrease the pump threshold of OPGs dramatically and may make OPGs reliable. The experimental demonstration in a LiNbO3 crystal shows that strong enough OPG can be obtained at pump intensity of only about 30GW/cm2 which is well below the crystal damage threshold Either a synchronized pulsed laser or a cw laser has been used as the scattering source, of which the wavelength, spectral shape and irradiating angle are not strictly required.展开更多
We propose and demonstrate a simple approach to lower the thermal quenching effect and improve the output power of Cr：LiSAF lasers, which is accomplished by employing two laser rods. The resonator contains two laser ...We propose and demonstrate a simple approach to lower the thermal quenching effect and improve the output power of Cr：LiSAF lasers, which is accomplished by employing two laser rods. The resonator contains two laser rods and is designed by using two ＂X＂ folding cavities in cascade. A tunable laser output of ～ 180 mW has been achieved with the pump of single-striped laser diodes. Compared with lasers using single gain rod, the laser with dual rods shows less severe thermal effect and increases the output by more than two times.展开更多
We report the scatterer concentration-dependent behaviour of laser action in high-gain scattering media.A modified model of random laser is proposed to explain the experimental results in good agreement.We may use thi...We report the scatterer concentration-dependent behaviour of laser action in high-gain scattering media.A modified model of random laser is proposed to explain the experimental results in good agreement.We may use this modified model to design and optimize random laser system.A further detailed model is needed to quantitatively analyse the far-field distribution of random laser action.展开更多
The transverse inhomogeneous carrier-envelope phase （CEP） distribution of idler generated through difference-frequency-generation （DFG） in quadratic nonlinear crystals is theoretically studied. In practical CEP st...The transverse inhomogeneous carrier-envelope phase （CEP） distribution of idler generated through difference-frequency-generation （DFG） in quadratic nonlinear crystals is theoretically studied. In practical CEP stabilized DFG setups, the pump and the signal are usually Gaussian beams with non-uniform intensity distribution. Since the idler CEP is dependent on gain, this non-uniform intensity distribution leads to inhomogeneous gain across the aperture of the idler beam, resulting in a varying transverse idler CEP. Simulation results show that in practical settings, in the high-gain regime, transverse inhomogeneous CEP can be much smaller compared with π/2. However, when gain on the propagation axis reaches saturation, CEP difference can well exceed π/2.展开更多
Stimulated Raman scattering （SRS） of a third-harmonic beam of a high-power laser in air is analysed by using a perturbation approach. It is found that intensity modulations of the third-harmonic beam, resulting from...Stimulated Raman scattering （SRS） of a third-harmonic beam of a high-power laser in air is analysed by using a perturbation approach. It is found that intensity modulations of the third-harmonic beam, resulting from the surface ripple of nonlinear crystal, can be significantly enhanced due to SRS, and the gain of instability increases with the spatial period of modulation. Numerical simulations based on the nonlinear coupled-wave equations verify the validity of the perturbation approach.展开更多
Temperature-insensitive phase-matching of second-harmonic generation(SHG)can be realized using two nonlinear crystals with opposite signs of the temperature derivation of phase mismatch.The design procedure for optimi...Temperature-insensitive phase-matching of second-harmonic generation(SHG)can be realized using two nonlinear crystals with opposite signs of the temperature derivation of phase mismatch.The design procedure for optimizing crystal lengths is presented,and full numerical simulations for the SHG process,based on realistic crystals,are performed at a typical high-power-laser wavelength of~1μm.It is suggested that the proposed two-crystal design can support high efficiency(60–70%)of SHG in the high-average power regime of a kilowatt.展开更多
基金Supported by the Science and Technology Commission Foundation of Shanghai under Grant Nos 05JC14005 and 05SG02, and the National Natural Science Foundation of China under Grant Nos 60538010, 10376009 and 10576009.
基金Supported by the Science and Technology Commission Foundation of Shanghai （Nos 05JC14005, 05SG02）, and the National Natural Science Foundation of China under Grant Nos 60538010, 10376009 and 10576009.
文摘We study a femtosecond Ti：sapphire laser pumped optical parametric amplifier （OPA） at 1053nm. The OPA Generates stable signal pulses with duration smaller than l OOfs, wavelength drift smaller than 0.5 nm, and pulseto-pulse fluctuation of about ±4%, by employinG an external seeder. In a terawatt laser pumped large-aperture LiNbOa OPA, pulse energy at signal has been scaled up to 4mJ. This m J-class femtosecond OPA at 1053nm presents a feasible alternative to optical parametric chirped-pulse amplification, and is ready to be applied to petawatt lasers.
基金Supported by the Ph.D. Programme Foundation of Ministry of Education of China, the Project on 0ptical Science and Technology of Shanghai （012261065）, and the National Natural Science Foundation of China under Grant No 10376009.
文摘Partially deuterated KDP is an ideal nonlinear crystal for second-harmonic generation （SHG） of femtosecond lasers at 1 μm, which features with vanished group-velocity mismatch at its retracing point of phase-matching. We numerically investigate the characteristics of SHG with femtosecond lasers in a partially deuterated KDP, which shows that group-velocity dispersion plays an important role. This spectrally non-critical phase-matching configuration can support both high efficiency and large acceptance bandwidth.
基金Supported the National Natural Science Foundation of China under Grant Nos 60538010 and 10576009, and the Science and Technology Commission of Shanghai under Grant Nos 05JC14005 and 05SG02.
文摘We have explicitly identified coloured conical emission （CCE） and noncollinear optical parametric generation （OPC） by spectrum characterizations. With an experimental setup providing different pump pulse durations, CCE and noncollinear OPG are observed both alternatively and simultaneously. Comparisons between CCE and noncollinear OPC are studied. Accumulation behaviour of modulational instabilities is observed in our two-crystal cascaded configuration, which results in enhancement or depression of the CCE formation.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10776005, 60725418 and 10576009, and the National Basic Research Programme of China under Grant No 2007CB815104.
文摘Cascaded nonlinear phase shifts may be imposed on the interacting waves during second-harmonic generation （SHG） in a quasi-Phase-matched （QPM） structure, whieh are severe in high-intensity regime and may result in lower conversion efficiency. We propose a configuration of QPM structure with reduced domain-length, which may depress the nonlinear phase shifts to some extent and lead to an improvement on the conversion efficiency. The numerical analyses on the conversion efficiency as well as the relative phase angle are discussed in detail for better understanding of the SHG process.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60538010, 10335030 and 10576009, and the Science and Technology Commission of Shanghai under Grant Nos 05JC14005 and 05SG02.
文摘We show analytically that in phase-mismatched second-harmonic generation, an effective diffraction is induced at the second-harmonic （SH） frequency. Numerical simulation results agree with the analytical predictions. Compared to the case of linear propagation, the effect of the overall diffraction at the SH frequency becomes doubled due to the induced diffraction, which causes an interesting result that the SH beam width will be larger than that of the fundamental field.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60538010, 60725418 and 10576009, and the Science and Technology Commission of Shanghai under Grant Nos 05JC14005 and 05SG02.
文摘Scattering-enhanced femtosecond optical parametric generation （OPG） has been observed and studied in detail, which may decrease the pump threshold of OPGs dramatically and may make OPGs reliable. The experimental demonstration in a LiNbO3 crystal shows that strong enough OPG can be obtained at pump intensity of only about 30GW/cm2 which is well below the crystal damage threshold Either a synchronized pulsed laser or a cw laser has been used as the scattering source, of which the wavelength, spectral shape and irradiating angle are not strictly required.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10376009 and 60538010） and the program of Shanghai 0ptical Science and Technology, China （Grant No 012261065）.
文摘We propose and demonstrate a simple approach to lower the thermal quenching effect and improve the output power of Cr：LiSAF lasers, which is accomplished by employing two laser rods. The resonator contains two laser rods and is designed by using two ＂X＂ folding cavities in cascade. A tunable laser output of ～ 180 mW has been achieved with the pump of single-striped laser diodes. Compared with lasers using single gain rod, the laser with dual rods shows less severe thermal effect and increases the output by more than two times.
基金Supported by the National Natural Science Foundation of China under Grant No.19734004.
文摘We report the scatterer concentration-dependent behaviour of laser action in high-gain scattering media.A modified model of random laser is proposed to explain the experimental results in good agreement.We may use this modified model to design and optimize random laser system.A further detailed model is needed to quantitatively analyse the far-field distribution of random laser action.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60890202, 60725418 and 10776005, and the National Basic Research Program of China under Grant No 2007CB815104.
文摘The transverse inhomogeneous carrier-envelope phase （CEP） distribution of idler generated through difference-frequency-generation （DFG） in quadratic nonlinear crystals is theoretically studied. In practical CEP stabilized DFG setups, the pump and the signal are usually Gaussian beams with non-uniform intensity distribution. Since the idler CEP is dependent on gain, this non-uniform intensity distribution leads to inhomogeneous gain across the aperture of the idler beam, resulting in a varying transverse idler CEP. Simulation results show that in practical settings, in the high-gain regime, transverse inhomogeneous CEP can be much smaller compared with π/2. However, when gain on the propagation axis reaches saturation, CEP difference can well exceed π/2.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10376009, 10576009 and 60538010.
文摘Stimulated Raman scattering （SRS） of a third-harmonic beam of a high-power laser in air is analysed by using a perturbation approach. It is found that intensity modulations of the third-harmonic beam, resulting from the surface ripple of nonlinear crystal, can be significantly enhanced due to SRS, and the gain of instability increases with the spatial period of modulation. Numerical simulations based on the nonlinear coupled-wave equations verify the validity of the perturbation approach.
基金Supported by the National Natural Science Foundation of China under Gratn Nos 61008017 and 60890202.
文摘Temperature-insensitive phase-matching of second-harmonic generation(SHG)can be realized using two nonlinear crystals with opposite signs of the temperature derivation of phase mismatch.The design procedure for optimizing crystal lengths is presented,and full numerical simulations for the SHG process,based on realistic crystals,are performed at a typical high-power-laser wavelength of~1μm.It is suggested that the proposed two-crystal design can support high efficiency(60–70%)of SHG in the high-average power regime of a kilowatt.
