Improve/Develop Metrology for VLA (Very Low Absorption) Coatings

"This SBIR Phase I Project will determine the feasibility of a novel instrument for measuring the quality of very low absorption (VLA) optical coatings. The instrument is based on the laser-induced surface thermal lens effect and will include a common-pathinterferometer to reduce sensitivity to alignment and mechanical vibrations. That will make this technique suitable for in-situ measurements during coating deposition. Detection sensitivity levels are similar to photothermal deflection and photo-acoustictechniques, for which absorbance levels of 0.1 ppm have been reported. The feasibility study will determine the optimal excitation and probe waveforms required for maximum signal-to-noise ratios. The proposed instrument allows determination of severaloptical, thermal and mechanical parameters, such as absorption, reflection, wavefront distortions, adhesion, and thin layer thermal conductivities. A compact fiber-optic design allows the proposed instrument to be easily retrofitted to existing coatingchambers. Signal detection can be performed outside the chamber, while information retrieval will be based on demodulation techniques used in related products developed by MetroLaser, such as the Laser Doppler Vibrometer, VibroMet¿, and a patentedwavefront sensor, the PhaseCam¿. High power lasers have become key devices in many industrial processes, and as a result, optical coatings are ever more becoming the critical components of such devi