By Michael Scobey, Peter Egerton and Rance Fortenberry
Narrowband filters are a critical technology for a variety of applications such as lidar (light detection and ranging), laser cleanup, chemical and gas sensing, instrumentation, and astronomy. Creating multicavity filters is a challenge for deposition process control systems. It invariably introduces undesirable ripple, resulting in signal loss in the pass band, the spectral range over which the filter has high transmittance. Alluxa uses a computer-controlled variation on the turning point method of thickness control for each individual layer, where the filter is constantly measured and variations in thickness compensated for, taking into account thickness errors associated with multiple layers.