Some effects of pulsed CO 2 laser heating of silica

Abstract

Silicon dioxide glass (silica) has been irradiated with pulsed multi-mode CO 2 laser light at wavelengths at 9.3 and 10.6 μm. These wavelengths fall within the restrahlen bands of silica. Electron paramagentic resonance spectra of irradiated samples contain the E′ 1 component (singly charged oxygen vacancies) which was not observed prior to irradiation. Dissolving the surfaces of irradiated samples with HF decreases the intensity of the E′ 1 component. The concentration of E′ 1 centers decreases with distance from the irradiated surfaces. The profile of concentration versus depth obtained by successive HF etching treatments shows a decrease by a factory of 3 between the surface and a depth of 0.2 μm. a constant concentration to a depth of 1 μm and then a decrease below detectable limits at 2 μm. An approximate calculation of temperature produced by the laser pulse at 9.3 and 10.6 μm shows that temperatures > 2000 K were produced at depths ∼ 0.5 μm. The high concentration of E′ 1 centers is attributed to the production of oxygen vacancies by high temperatures produced by the laser pulses and the subsequent rapid cooling.