为了准确地确定飞秒激光对比度的信息,基于两束不同激光的互相关原理,利用非线性晶体对激光强度变化十分敏感的特性,研制了一台三阶相关仪,并用其对钛宝石激光放大系统输出的飞秒激光脉冲进行了测量,得到了有关该系统的强度对比度的信息.结果显示:该系统输出的激光对比度在10⁶左右,在脉冲的前沿和后沿有很强的ASE辐射,并且延续了很长的一段时间;种子脉冲的对比度在10⁵左右,而且在主脉冲前约2ps的位置上,有一个强度很低的小脉冲,在主脉冲的两翼各有一个非常小的台阶.

A third-order correlator is built based on the technique of cross-correlation between the fundamental and second harmonic waves of femtosecond lasers.Using this correlator,the contrast ratio of femtosecond laser pulses from a typical CPA laser system is measured.The measurements show that the contrast ratio of the system is about 10⁶.There is a strony ASE beside the main pulse,lasting for a long time.The seed contrast ratio is about 10⁵.There is a little pulse at the 2ps before the main pulse and a small stage at the two sides of main pulse.