Low intensity laser pulse train propagation in air: part II: experimental studies

Abstract

This paper discusses the results of experimental studies of low intensity laser pulse train (LI-LPT) propagation in air. The train of ultra-short laser pulses of adjustable repetition rate became possible with the intra-cavity longitudinal mode selector that improves the efficiency of the mode locking mechanism. This technique enabled the generation of a LPT with an envelope duration TPL  40 ns (FWHM). The envelope is filled with a train of micro-pulses that form a temporal comb with an individual micro-pulse duration L  150 ps. The micro-pulse separation time, TP, can be tuned from ~10 ns to 0.45 ns. Depending on the pump level, the total energy ELPT of the LPT is in the range of 150 mJ and 1.2 J. When focused in air, the LPT with peak micro-pulse intensity ranging from 510 14 W/cm 2 to 10 16 W/cm 2 generates a plasma. The laser induced plasma leads to laser light scattering, broadband luminescence, and generation of rf radiation. We report the first results of the experimental studies of the interaction of the LI-LPT with air. Theoretical analysis and simulations of the filamentation and rf radiation have been carried out. The results of the experiment are in agreement with the theoretical and simulation results.