Abstract: Apparatus and a method are disclosed for continuously varying the output radiation frequency of a scanning laser system about a selected nominal output radiation frequency with a calibrated scan. Apparatus is disclosed for continuously varying the resonant frequencies of both the laser cavity and the reference cavity, for controlling this scanning and for calibrating the scan width. A method for calibrating the scan width is also disclosed.

Abstract: A Fabry-Perot etalon is mounted within the optical cavity of a laser for selecting the wavelength of the output radiation of that laser from a plurality of discrete wavelengths closely distributed about a nominal wavelength. The etalon includes a pair of closely spaced prisms mounted along the optical axis of the laser cavity with the laser beam passing therethrough. Each of the prisms has a first surface facing outwardly of the etalon and inclined at a slight angle to a normal to the optical axis, and each prism includes a second surface opticaly adjacent and spaced from the second surface of the other prism, each such second surface being inclined relative to its respective first surface.