Past Events

Abstract
 

The filament propagation of a pulsed laser in medium, which means that the laser keeps narrow beam width and high peak intensity over a unusual long propagating distance which can be many times of the Rayleigh length, have been observed in many medium. For explaining the filament propagation, many in debate models have been proposed, such as moving focus model, self-channeling model, and self-focusing-refocusing model.

In this seminar we report the observation of self-focusing and refocusing effect in ZnO crystal incident with converging femtosecond laser. The green two-photon luminescence of ZnO make the propagation of laser pulse with maximum intensity at focusing positions visible. Two separated focusing points were found on the laser propagation axis. The first focusing point occurs at a position before the natural diffraction focus which indicates that the self-focusing happens, and the second focusing point is caused by the refocusing effect. These experimental results can be seen as evidences for the refocusing model of the laser filament propagation.  

Anyone interested is welcome to attend.