采用抽运探测光路,实验研究发现飞秒脉冲激光和连续激光在铬膜表面抽运激发后,当激光功率达到一定程度时,在探测光的透射方向看到了明显的中心暗斑衍射现象。而在没有抽运光激发时,这种暗斑衍射现象又消失。采用二元相位板的理论对这种可逆衍射现象进行了解释,发现低能量密度的飞秒脉冲激光会比高能量密度的连续激光诱导更大的相位变化。实验结果和理论分析均有助于理解弱飞秒脉冲激光及连续激光和铬膜的相互作用的机制。

A pump-probe setup is used for experimental study and it is found that an obvious dark-center diffraction appears at the transmission direction of probe beam when the chromium films is excited by the femtosecond pulse laser and the continuous-wave (CW) laser and when the laser power reaches a certain level. While the dark diffraction phenomenon disappears without the pump beam. This reversible diffraction phenomenon is explained by using the binary phase plate theory. It is also found that the phase change induced by the femtosecond pulse laser is larger than that by the CW laser. The experimental and theoretical results can contribute to understand the mechanism of the interaction between the chromium films and the femtosecond pulse laser and the CW laser.