光折变晶体中ps激光脉冲二波耦合增益正负转换现象

用二列脉宽为60ps的连续锁模Nd:YAG激光的倍频光在掺Ce的KNSBN晶体中进行二波耦合.当泵浦光脉冲迟于信号光脉冲到达晶体,或泵浦光脉冲虽先于信号光脉冲到达晶体.但时间提前量小于激光脉冲半高宽时.信号光的二波耦合平均增益是非负的;当泵浦光脉冲先于信号光脉冲到达晶体且时间提前量大于激光脉冲半高宽时.信号光的二波耦合平均增益可变为负的.对此给出物理解释.

Positive and Negative Gains Transition of ps Laser Pulses Two-wave Coupling in a Photorefractive Crystal

In a Ce : KNSBN crystal, two-wave coupling was carried out using two laser beams from a frequency-doubled cw modelocked Nd:YAG laser, with 82 MHz repetition rate and a pulse duration >t =60 ps. When the time delay t of the pump laser pulses with respect to the probe ones is >0, the average gain of the probe beam is >0. And when t <- >t, the average gain can be <0. A physical explanation is put forwards.