Thermal modeling of laser-densified microlenses

Abstract

A three-dimensional transient thermal modeling of laser-densified gel-silica microlenses is described. This model simulates the three-dimensional temperature distribution in a porous gel-silica glass irradiated by a CO(2) laser. The heat induced by the laser gives rise to a gradient in temperature, which creates a gradient in density and index of refraction. The laser-densified region functions as a microlens. The modeling results include a temperature distribution with time within a volume of 2 mm × 2 mm × 2 mm. The calculated temperature distributions compare well with the measured property distributions of the microlens including microhardness and the peak positions of the Si-O-Si stretching vibration mode in IR spectra across the lens.

Structural evolution of a porous type-VI sol-gel silica glass

“…The shift in the peak to higher wave numbers with an increase in processing temperature is a measure of the densification of the material [4,22]. Chia et al have reported a PP at 1122 cm -~ for a fully dense pure commercial optical silica [23]. A PP at 1123.3 cm -1 for the 30 ,~ type-VI matrices indicates that, at least at its surface, this material reaches a density higher than the melt glass density, confirming the results from the helium pycnometer.…”