Multi-Frame Observation of a Single Femtosecond Laser Pulse Propagation Using an Echelon and Optical Polarigraphy Technique

We developed a multiframe observation method of femtosecond laser pulse propagating in transparent medium based on optical polarigraphy technique. An echelon was introduced into the probe light and divided it into multipulses both in time and space, allowing a multiframe detection of the intense laser pulse propagating in materials. Using this method, we realized a multiframe observation of a single femtosecond laser pulse propagating in CS2 with ultrafast self-modulation such as filamentation. This imaging method has been demonstrated to be of a femtosecond time resolution and a frame rate of ~ THz.

I. Introduction

In the past few decades, many methods have been developed to observe the propagation behavior of intense laser pulses in transparent media [1]–[3]. Femtosecond time-resolved optical polarigraphy (FTOP) technique, which uses the instantaneous birefringence induced by the strong electrical field of the pulse, can be used to measure the ultrafast temporal changes in the two-dimensional spatial distribution of the optical pulse intensity [4]–[6]. If a series of instantaneous intensity distributions at several successive temporal points are observed, however, the propagation profile will be quietly different from shot to shot due to the laser pulse fluctuation. To fulfill the single-shot detection of the pulse propagation dynamics, M. Fujimoto et al. developed a successive four-frame instantaneous observation method of an intense pulse propagating in air [7]. This method used a quadruple-pulse generator in the optical path generating a quadruple-probe pulse, which captures successive four-frame instantaneous FTOP images of a single laser pulse. However, the quadruple-pulse generator which combines four different probe beams with different optical paths, will largely increase the complexity of the experiments.