Track Formation in Optical Glass Caused by Electrostrictive Laser Beam Self-Focusing

摘要

An electrostriction mechanism for laser beam self-focusing and track formation in transparent optical glass is analyzed theoretically. Electrostrictive self-focusing occurs when a laser pulse of sufficiently high power and rapid rise time passes through a transparent medium. During self-focusing, the beam collapses to a small radius, leaving a track of permanent damage. Typical tracks have a diameter of a few wavelengths of light and extend up to several centimeters. The propagation of the beam is described by a new 'small-scale' beam tracing equation, derived from Maxwell's equations. The equation includes the effect of the inhomogeneous index term of the vector light wave equation as well as beam diffractive. For steady-state Kerr and electrostrictive trapping, the new equation gives experimentally correct filament diameters. A trapping threshold is derived for three pulse shapes, covering the steady-state, transitional, and transient regimes of pulse duration and beam size. A formula for computing the power to achieve a given maximum intensity is derived. A computer movie of beam trapping shows the collapse of the beam during self-focusing. (Author)