互相关法实现超短脉冲精确延时的探测及控制

在超短超强激光装置中, 强激光与靶物质相互作用产生等离子体, 为了获知等离子体的演化规律, 需要准确控制探针光与打靶主激光的相对延时, 精度须达到几十飞秒至几皮秒。为此设计了一台延时测量仪, 该测量仪基于超短脉冲强度二阶单次互相关测量原理, 利用非线性晶体的非共线和频效应, 采用线阵CCD采集探针光与打靶光产生的和频光空间光强分布曲线, 通过测量和频光强峰值的相对移动量, 反映探针光与打靶光的相对延时, 控制延时光路达到两光束的精确延时。详细阐述了该延时测量仪的构型, 讨论了超短脉冲强度互相关测量的原理, 理论分析了两光束的相对时间差与和频光峰值相对移动量之间的关系, 通过数值模拟给出了两光束夹角对延时测量精度的影响, 可根据不同要求改变两光束夹角更换晶体, 以满足延时精度及延时范围的要求。在理论分析的基础上进行了初步的实验验证。

Using Crosscorrelation to Detect and Control the Accurate Delay Time of Ultrafast Pulses

In the high-power ultrafast laser system, interaction between the high-power laser and target substance would produce plasma,in order to know the evolvement of the plasma,the delay time between probe laser and main laser should be controlled accurately, in which the precision of delay need to be several picoseconds even several femtoseconds. Therefore an instrument, which was based on the ultrafast pulses crosscorrelation theory, by utilizing the sum frequency generation effect, CCD to collect the spatial intensity distribution of sum frequency beam, was designed. By measuring the shift of curve peak, the delay between fundamental beams can be calculated, the fundamental beams can be accurately delayed by controlling the optical layout. The conformation of delay instrument was described, the principle of the ultrafast pulses crosscorrelation measurement was discussed, the relationship between the delay time and the shift of the curve peak was analyzed theoretically. The influence on the measure precision caused by the angle of fundamental beams was discussed numerically, to reach a much more accurate delay time, we can change the nonlinear crystal according to the beam angle.