Long distance filamentation of 400 nm femtosecond laser pulses in air

• DOI: 10.1007/s00340-009-3663-0
• Publication Date: 2009-08-03T13:25:36Z
• Authors: Z. Zhang; X. Lu; T.-T. Xi; W.-X. Liang; Z.-Q. Hao; Y. Zhang; M.-L. Zhou; Z.-H. Wang; J. Zhang
• Keywords: Filamentation; Diaphragm (acoustics)

The characteristics of the light filaments formed by λ=400 nm blue femtosecond laser pulses are experimentally investigated. Both pre-focused and free propagation conditions are studied. The diameter, length and electron density were measured by using fluorescence signal imaging and longitudinal diffraction method. About 2×1017 cm−3 electron density in filaments was achieved with beam pre-focusing. In the free propagation case, the multi-filamentation can be observed over 70 m propagation distance, and the energy in the filament core is only about 30 μJ. The effects of energy reservoir on the filament core have been investigated by inserting a diaphragm in a selected single filament path to block the energy of the reservoir. The evolution of filamentation has been studied experimentally as a function of diaphragm size. The energy reservoir can be extended to about 10 mm from the filament core. The results indicate that the up conversion of laser is a possible way to enhance the utilization of laser energy for the generation of long filaments.