Improve/develop metrology for VLA (very low absorption) Coatings

The development of fast, reliable, accurate and non-destructive absorption measurements is critical to the development of very low absorption/high laser damage threshold optical thin films for HEL and other high value applications. The objective of this research project is to continue development of a practical method for quickly and accurately measuring the very low absorption in optical thin films as they are being deposited inside a vacuum chamber. In Phase I, an attenuated total internal reflection-waveguide (ATIR-W) technique was shown to enhance the absorption of a single thin zirconia film more than 300 times, compared to its single pass absorption at near normal incidence. Theory indicates that a film with normal incidence absorption of 1 ppm, when placed in an optimized ATIR-W instrument, will absorb 10,000 times the light or 1%, making direct measurement of the reduction in the reflected beam (absorption) practical. With this real time information, coaters can expedite the optimization of the coating materials, processes and designs. Phase II will continue the development of these TIR-W techniques by testing both wavelength scanning at a fixed angle of incidence and angle of incidence scanning with monochromatic light.