Multiple refocusing of femtosecond filamentation in air: Experiment and simulation

Multiple refocusing of intense femtosecond laser pulses in air was studied both experimentally and numerically. Using fluorescence measurement and acoustic diagnostics simultaneously, filamentation and multiple refocusing of laser pulses were observed. It is found that the refocusing phenomenon is attributed to the dynamic transformation of laser energy over the transverse beam section. The roles of the different regions of the beam cross section were further analyzed.