All-optical investigations of intense femtosecond pulse ionization in transparent dielectrics with applications

Abstract

Large band gap optical media are transparent to near-infrared (NIR) and optical light pulses in the linear regime. However, at sufficiently high intensities, in their interaction with femtosecond (fs) laser pulses, nonlinear absorption takes place by multi-photon processes as well as field-assisted processes such as tunnel- and collisional-ionization. Their transparency to NIR and optical fs pulses enables in situ studies of nonlinear photoionization inside these media by all-optical transmission measurements. These measurements in tandem with suitable phenomenological models has paved the way towards a deeper understanding of dynamical processes. The ensuing dynamics can be categorized into two timescales: the first is a long pulse regime, for temporal duration t_{p} > 100 fs, where laser driven electrons in these media gain sufficient kinetic energies by mechanisms such as inverse bremsstrahlung leading to electron avalanches. In the short pulse regime, t_{p}< 100 fs, these electrons are excited to the conduction band by multiphoton absorption. In this article we present a perspective of the current status of research as well as results from our investigations. Not only do these studies provide facile means to study intriguing nonlinear photoionization processes, but they also probe these systems in a regime of intensities and pulse widths where micro- and nano-structuring as well as processing of materials by fs pulses are often realized. Further, these methods compliment research on coherent processes such as the generation of high-order harmonics and attosecond pulses in condensed phase media.