Propagation of a filamentary femtosecond laser beam with high intensities at an air-solid interface

Abstract

The propagation of a filamentary laser beam at an air-glass surface is studied by setting the incident angle satisfying the total reflection condition. The images of the trajectory of the filamentary laser beam inside the sample and the output far-field spatial profiles are measured with varying incident laser pulse energies. Different from the general total reflection, a transmitted laser beam is detected along the propagation direction of the incident laser beam. The energy ratio of the transmitted laser beam depends on the pulse energies of the incident laser beam. The background energy reservoir surrounding the filament core can break the law of total reflection at the air-glass surface, resulting in the regeneration of the transmitted laser beam.OCIS The self-guided propagation of intense femtosecond laser pulses in transparent media results in the generation of extended plasma channels that have exciting potential applications in the field of fundamental nonlinear optical physics [1][2][3][4][5] . A single and stable filament can be generated by using a conventional lens reaching a few tens of millimeters or even meters, if the laser intensity exceeds the critical power P cr . Multifilaments will be formed as the incident pulse exceeding the critical power by an order of magnitude, which is unstable both in space and time [6] . Investigations on the characterization of a single filament with the incident laser power P ≥ P cr and the interactions among multifilaments were performed to search for further applications of laser filamentation, e.g. amplified spontaneous emission air lasing in both the backward and forward directions [7,8] . Meanwhile, the propagation characteristics were also studied. Polynkin et al. experimentally observed the generation of curved plasma channels in both air and water by applying femtosecond Airy beams [9,10] . An extended and robust thermal waveguide structure in air with a lifetime of several milliseconds can be formed with femtosecond filaments [11] , making possible the very-long-range guiding and distant projection of high-energy laser pulses and high average power beams.However, the propagation characteristics of high power pulsed lasers at the interfaces of different transparent materials are ignored, particularly those of femtosecond filament. The air-glass surface is now widely used for the imaging of the lateral distribution of a filament [12][13][14] ; however, the propagation characteristics are neglected. Setting the incident angle satisfying the total reflection condition, the propagation of a femtosecond filament at an air-glass surface is studied by showing the imaging of the propagation trajectory, the far-field profiles in this Letter. The dependence of the pulse energy of the reflective beam on the incident pulse energy is also measured. Figure 1 shows the experimental setup. The basic parameters of the femtosecond laser beam are a pulse energy of 1.1 mJ, a central wavelength of 800 nm, a pulse duration of 60 fs, and a repetition rate of 1.0 kHz. One set of ...