BBOⅠ类相位匹配非共线参量产生中的群速自匹配

Group velocity self-matching in noncollinear optical parametric generation with a type-Ⅰ phase-matched BBO crystal

利用重复频率为1kHz的钛宝石激光的倍频蓝光抽运Ⅰ类相位匹配的偏硼酸钡(BBO)晶体,获得了可见光区的非共线参量超荧光.给出了最强光强处参量超荧光的非共线角,波长随相位匹配角的变化.理论计算了在参量超荧光中三波的群速失配随非共线角和相位匹配角的变化规律.结果表明,Ⅰ类非共线相位匹配的参量超荧光关于抽运光中心对称.并且沿光强最强的参量超荧光方向三波的群速失配最小,有效互作用长度最大,即参量超荧光的强度角分布是三波的相速和群速自匹配的结果.该理论和实验研究为减小飞秒光参量放大中三波的群速失配提供了一个理想的几何模型,为获得高增益、窄脉冲宽度的参量光输出提供了理论依据和实验验证.

Noncollinear parametric superfluorescence （NPS） is obtained in the visible region by pumping a type-Ⅰ phase-matched BBO crystal with the second harmonic of an amplified Ti ： sapphire laser at 1 kHz repetition rate. The variation of the noncollinear angle and the wavelength at the peak intensity of the NPS with the phase-matched angle is studied, and the variations of the group velocity mismatch （GVM） with the noncollinear angle and the phase-matched angle in the three-wave interaction is calculated theoretically. The results indicate that the type-Ⅰ phase-matched NPS ring is centrosymmetric with respect to the pump beam on the observation screen. Along the NPS direction at the peak intensity, the GVM is minimal and the effective interaction length is maximal for the three waves. The angular distribution of the NPS intensity is ascribed to phase velocity and group velocity self-matching among interacting pulses. The theory and the experiment provide an ideal geometrical model for reducing the GVM between three waves, and provide a theoretical guidance and experimental verification for obtaining parametric pulses with higher gain and shorter duration in femtosecond optical parametric amplification.