Characterization of scandium oxide thin films for use in interference coatings for high-power lasers operating in the near-infrared
Date
2010
Authors
Krous, Erik M., author
Menoni, Carmen S., advisor
Marconi, Mario C., committee member
Williams, John D., committee member
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Abstract
The work presented in this thesis aims to investigate scandium oxide (scandia), deposited using dual ion beam sputtering, as a high-index material for interference coatings to be implemented in high-power lasers. Ion beam sputtered scandia coatings have the potential to allow for the power scaling of high-power lasers operating in the near-infrared. Ion beam sputtering is the technique currently used by many commercial companies to produce low-loss, high-damage-threshold coatings required by lasers operating with high fluences. The development of scandia, and other thin film materials, requires the reduction of defects in the material through modification of growth processes and post deposition treatment. Material defects give rise to absorption of laser light and laser induced damage initiation sites. The growth parameter investigated in this work is the oxygen partial pressure in the deposition chamber during the reactive sputtering process of a metal Sc target to form Sc2O3. The film properties are sensitive to the oxygen partial pressure. At 2 μTorr oxygen partial pressure, the films are metallic and highly absorbing with an absorption, at λ = 1.064 μm, of > 104 ppm. The absorption decreases to 10 ppm at 5 μTorr oxygen partial pressure and at 38 μTorr, the absorption reaches a value of 35 ppm. This, along with the increase in absorption near the optical band edge, suggests an increase in shallow-type defect concentrations for increasing oxygen partial pressures. The observed defects contain unpaired electrons, as assessed by electron paramagnetic measurements, that have a paramagnetic absorption signal with principle g-values [gxx, gyy, gzz] = [2.018, 2.019, 2.058]. Generally, the concentration of the paramagnetic species increased with increasing oxygen partial pressure. These spin defects are possibly O2̅ interstitials in the deposited films. These defects contribute to an approximately 40% increase in the film stress observed in x-ray diffraction measurements and measurements of stress-induced fused silica substrate curvature.
Description
Department Head: Anthony A. Maciejewski.