Optical characterization of damage resistant 'kilolayer' rugate filters

摘要

Multilayer dielectric optical coatings produced by high temperature plasma-assisted chemical vapor deposition (PCVD) have been previously shown to have very high surface and bulk damage thresholds (above 40J/cm(sup 2)). Because these experimental coatings are deposited on tubular substrates, conventional wavelength scanning cannot accurately measure the coating peak reflectance and bandwidth. Measurement of the variation of transmittance with incidence angle at fixed wavelength permits analysis of the coating spectral response. The results indicate that the PCVD coatings behave as nearly ''ideal'' rugate filters. Their optical performance agrees well with that predicted for a rugate by Southwell's coupled-wave theory and by the characteristic-matrix model. These 1000-layer-pair filters have maximum reflectances exceeding 99.9%, peak reflectance wavelengths within 0.5% of the design wavelength, and FWHM bandwidths narrower than 10 nm. Minor perturbations to the ideal rugate sinusoidal profile do not appreciably affect the coating optical performance. Comparison with calculations suggest that the only significant deviation of the PCVD structure from that of an ideal rugate is a small (0.7%) drift in the index period. Excellent optical performance and high damage resistance makes PCVD rugate coatings potentially useful for several high power laser applications. 13 refs., 7 figs.