啁啾补偿飞秒脉冲高效三次谐波产生

中心波长为800 nm、脉宽为60 fs、重复频率为10 Hz的飞秒激光分为强弱两束,能量较强一束经I类相位匹配的BBO晶体倍频,之后与另一束光非共线和频得到三次谐波输出.实验得出基频和倍频光能量达到最佳配比时,三次谐波的转换效率最大;系统输出激光携带一定负啁啾可以补偿色散,提高三次谐波的转换效率.最终,当基频和倍频光的能量分别为2.38 mJ和0.588 mJ,系统输出激光带有9.66×10<'3> fs<'2>的负啁啾时,得到了中心波长为267 nm、单脉冲能量为230μJ的三次谐波输出,其转换效率高达19%.

High Conversion Efficiency of Third Harominc Generation Using Femtosecond Laser Pulse with Chirp Compensation

The laser beam from Ti:sapphire laser with pulse width of 60 fs, repetition of 10 Hz and wavelength of 800 nm, is splitted into a strong beam and a weak one. The former is frequency-doubled in type-I phase-matched BBO crystal, and then the third harmonic is achieved by the non-collinear frequency-sum of the fundamental wave (800 nm) and the second harmonic generation (400 nm). The sum-frequency efficiency reaches the maxium value when the optimal ratio of fundamental wave and second harmonic is realized. The negative chirp introduced by the fundamental wave can compensate partially dispersion and improve conversion efficiency. When the pulse energy of 800 nm and 400 nm are 2.38 and 0.588 mJ respectively, a single pulse energy of 230 mJ at 267 nm is obtained with group velocity dispersion of -9.66×103fs2 and conversion efficiency of 19%.