应用波分复用技术实现飞秒级超快动态过程的脉冲数字显微全息记录

Pulsed Digital Micro-Holography for Femtosecond Order Ultrafast Process Recording by Using Wavelength Division Multiplexing Technology

采用波分复用方法实现飞秒级超快动态过程的脉冲数字显微全息记录和再现。在全息记录过程中,利用BBO倍频晶体对入射激光进行倍频,将基波和谐波分光,并经时间延迟后进入迈克耳孙干涉仪,从而可应用波分复用技术,先后在CCD的一帧图像上记录两张具有不同空间频率的子全息图。采用这种方法,实现了对单脉冲飞秒激光激发空气电离的超快动态过程的全息记录,并通过数字傅里叶变换和数字滤波的方法,分别再现出每张子全息图记录的波前,从而获得了具有飞秒时间分辨的空气等离子体形成和传播过程的动态振幅和相位图像,其单次曝光时间为50 fs,曝光时间间隔为400 fs,相应的曝光频率约为2.5×1012f/s。

Wavelength division multiplexing （WDM） used in an ultrashort pulsed digital micro-holographic system to record and represent ultrafast processing of femtosecond scale is reported. A BBO crystal is used to generate the harmonic wave of the incident laser wave, and both the basic and doubled frequency waves are separated, then timedelayed respectively and introduced to a Michelson＇s interferometer to record two sub-holograms with different spatial frequencies on a single frame of a CCD by means of WDM. In the experiment, an ultrafast dynamic process of air ionization induced by a single femtosecond laser pulse is holographically recorded, and both intensity and phase images of the digitally reconstructed images are obtained through Fourier transformation and digital filtering, which show clearly the dynamic process of the plasma forming and propagating, with a time resolution of femtosecond scale. The related parameters are, exposure time 50 fs, exposure interval of 400 fs, as well as exposure frequency of 2.5 × 10^12 f/s.