飞秒BBO光参量放大中闲频光二次谐波的产生

由于相位匹配条件和非线性晶体透光范围的限制，400nm蓝光抽运的飞秒β-BaB₂O₄（BBO）光参量放大（OPA）输出的参量光调谐范围有限，很难得到波长小于460nm的蓝光和近紫外光.实验采用1kHz钛宝石九通啁啾脉冲放大器的倍频蓝光作抽运光，超连续白光 作种子光，在Ⅰ类非共线相位匹配条件下，利用宽带的飞秒BBO OPA，在一定的实验参数下 获得了530—810nm放大的信号光，以及810nm—17μm波段范围的闲频光.与此同时 ，还获得了410—700nm连续可调的闲频光的二次谐波，其与闲频光层叠分布，单脉冲能量 为26μJ，转换效率大于5%.仅利用单块晶体的飞秒BBO OPA就可以获得410—810nm连 续可调的飞秒脉冲输出，从而为更多研究和应用的需要提供了重要的光源.对飞秒光参量放 大中闲频光二次谐波产生的条件也进行了理论分析. 关键词： 二次谐波 闲频光 非共线相位匹配 飞秒光参量放大

Idler second harmonic generation in femtosecond BBO optical parametric amplification

For femtosecond optical parametric amplification (OPA) pumped with a 400nm blue laser, limited by phase-matched condition and nonlinear crystal transparent range, the tuning range of the output parametric laser is restricted, and the blue and the near UV lasers with wavelength less than 460nm are difficult to obtain. In our experiment, we adopted the second harmonic of a Ti:sapphire nine-pass chirp pulse amplifier at 1kHz repetition rate as the pump beam, and the white- light supercontinuum as the seed beam; thus, by a type-Ⅰ noncollinear phase-mat ched broad bandwidth β-BaB₂O₄ (BBO) OPA, with certain exp erimental paramete rs, the amplified signal beam from 530nm to 810nm and the idler beam from 81 0nm to 17μm were obtained; at the same time, the idler second harmonic fr om 410nm to 700nm was obtained also. The idler second harmonic was cascaded with the idler beam, its pulse energy was 26μJ and the conversion efficienc y was greater than 5%. Therefore, femtosecond pulses tuned continuously from 410 nm to 810nm can be obtained by the BBO OPA with a single crystal only, there by a useful source is provided for more investigations and applications. In this paper, we also have theoretically analyzed the generation condition of the idle r second harmonic for femtosecond OPA.