基于氧化镁晶体中级联四波混频过程的紫外飞秒光脉冲产生

紫外波段飞秒激光脉冲是研究超快化学和超快物理相关过程的重要工具,实现波长可调谐的宽带紫外飞秒光脉冲将有助于推动超快动力学及相关领域的研究.本文报道了以两束400 nm的飞秒光脉冲作为级联四波混频的抽运源,在氧化镁晶体中产生9阶频率上转换和5阶频率下转换边带信号的实验结果.边带波长范围从350 nm到450 nm连续可调谐,这些边带信号的发散角和波长与级联四波混频理论预测结果吻合.紫外边带相对于入射光的整体转化效率约为1.2%.同时,高阶边带的光谱形状呈现高斯型,其谱宽理论上支持傅里叶转换极限脉宽为20—50 fs.本文展示了一种高效产生波长可连续调谐的紫外飞秒光脉冲的便捷方法,为基于紫外超短脉冲的相关研究提供了有效工具.

Generation of tunable ultraviolet femtosecond pulse in MgO crystal by cascaded four wave mixing

Ultraviolet femtosecond laser pulse is an important tool in studying ultrafast chemical and physical processes.Realizing broadband ultraviolet laser pluses with a wide tunable range would significantly facilitate the study of ultrafast processes.As an effective and convenient method,the cascaded four-wave mixing(CFWM)has been widely adopted to generate broadband and tunable ultraviolet femtosecond laser pulses.In this work,we carry out CFWM in MgO crystal by using two 400-nm pulses to generate tunable ultraviolet femtosecond pulse.The MgO crystal is chosen due to its high third-order nonlinear susceptibility,large band gap and high transmittance in the ultraviolet region.In the experiment,nine frequency up-converted and five frequency down-converted sidebands are observed.The measured wavelength and scattering angle of each sideband are consistent with the CFWM theory predictions.The wavelength range of the sidebands covers 350–450 nm.The total conversion efficiency of the ultraviolet sidebands is 1.2%,which is higher than the reported values with visible/near infrared driven lasers.Meanwhile,the spectra of the high-order sidebands present a Gaussian profile and can support a Fourier-transform-limited pulse duration of less than 50 fs.Besides,the central wavelengths of the sidebands can be effectively tuned by adjusting the time-delay between the two pre-chirped pump pulses.Our study provides an efficient and convenient scheme to generate short ultraviolet femtosecond pulses with a wide tunable range.