Systematic study of spatiotemporal dynamics of intense femtosecond laser pulses in BK-7 glass

Abstract

In this paper we present a systematic study of the spatial and temporal effects of intense femtosecond laser pulses in BK-7 over a broad range of input powers, 1-1000 times the critical power for self-focusing (Pcr) by numerically solving the nonlinear Schrödinger equation (NLS). Most numerical studies have not been extended to such high powers. A clear-cut classification of spatio-temporal dynamics up to very high powers into three regimes -the group-velocity dispersion (GVD) regime, the ionization regime and the dominant plasma regime -as done here, is a significant step towards a better understanding. Further, we examine in detail the role of GVD in channel formation by comparing BK-7 to an 'artificial' medium. Our investigations bring forth the important observation that diffraction plays a minimal role in the formation of multiple cones and that plasma plays a diffraction-like role at very high powers. A detailed study of the spatio-temporal dynamics in any condensed medium over this range of powers has not been reported hitherto, to the best of our knowledge. We also suggest appropriate operational powers for various applications employing BK-7 on the basis of our results.

Focal dynamics of multiple filaments: Microscopic imaging and reconstruction

“…For the purpose of clarifying the role of tight focusing in the multiple filamentation process, we reconstructed these observations by means of numerical simulations based on different paraxial or nonparaxial propagation models [9,13] for linearly or circularly polarized pulses [22,33], which all take the form of an unidirectional propagation equation for the Fourier components of the pulse envelopeÊ(k…”

“…For instance, numerous properties of light filamentation constitute unique features for potential applications [1,2] such as remote secondary sources of radiation in the terahertz domain [3] and generation of few-cycle pulses and extreme ultraviolet radiation [4][5][6]. To date, attention has mainly been focused on long-range filament dynamics for unfocused and loosely focused (focal length >1 m) intense laser beams [7][8][9] for which control mechanisms were proposed [10]. Very few experimental studies have examined ultrashort laser pulse filamentation with tightly focused beams [11,12].…”

Ultrafast light-matter interaction in transparent medium

“…For the cases of the slowly-varying envelope approximation, the propagation equation for the pulse envelope can be reduced to the nonlinear Schrödinger (NLS) equation from the wave equation using the well-known arguments [12,14,15]. The NLS equation could be extended to include the effects of ionization and the effects of the influence of electron plasma on the pulse envelope and takes the form…”

“…The studies of Chiron et al [12], Couairon et al [14] and Kumagai et al [15] justify retaining only the transverse Laplacian in the space-time focusing term for longer pulse widths, 100 fs or longer, when it is of interest to study only the spatio-temporal dynamics for pulses that are not in the few cycle limit. For the same reason, we can ignore the third-order GVD, selfsteepening and Raman response.…”

“…This necessitates a complete understanding of the physical processes that govern the spatio-temporal dynamics of the intense ultra-short pulse in the medium. The theoretical description of laser-induced refractive index changes in the interaction of high-intensity laser pulses with plasma was considered by many authors [12][13][14][15]. The spontaneous breakup of highly elliptical laser beams into one-and two-dimensional arrays of light filaments was studied in fused silica [16], where the multiple filamentation process is initiated by random intensity modulation across the beam "amplitude noise".…”