Damage formation on fused silica illuminated with ultraviolet-infrared femtosecond pulse pairs

Abstract

We investigate damage formation on the surface of fused silica by two femtosecond laser pulses, a tightly focused 266 nm (UV) pulse followed by a loosely focused 800 nm (IR) pulse. We show that the damage size is determined by the UV pulse, and only a small fraction of the normal UV damage threshold energy is needed to cause damage when combined with the properly delayed IR pulse. Our results, analyzed with a rate equation model, suggest that the UV pulse generates seed electrons through multiphoton absorption and the IR pulse utilizes these electrons to cause damage by avalanche ionization. By tuning such parameters like pulse energy, time delay, IR pulse duration and polarization, we further demonstrate that damage profile can be controlled.

Overcritical plasma ignition and diagnostics from oncoming interaction of two color low energy tightly focused femtosecond laser pulses inside fused silica

“…In this case the corresponding third harmonic signal is registered. The micromodification dimensions prove that the laser-affected zone is determined by the SH laser pulse which corresponds to the data known in literature [8,12]. Thus, one can conclude that only with 0.5E th of the SH laser pulse energy and 0.65E th of the IR the absorbed energy density reaches the value of 4.5 kJ cm −3 , which is enough for phase transition occurrence and micromodification formation in a bulk of the sample.…”

Enhancing nonlinear energy deposition into transparent solids with an elliptically polarized and mid-IR heating laser pulse under two-color femtosecond impact

“…The main challenge for the two-colored method is to use the IR pulse to assist the short wavelength pulse without pre-ionization of the sample by the IR pulse itself. Therefore, the higher damage threshold for the elliptically polarized laser pulses provides us with the opportunity to increase the IR pulse energy, and this might further reduce the short wavelength damage threshold [12]. Thus, the use of an elliptically polarized IR pulse under the threshold energy allows us to transfer more energy to seed electrons through avalanche ionization without blurring the excitation footprint.…”