Parallelism maps for optically contacted etalons

A measurement technique is described that is capable of producing accurate numerical maps of the parallelism defect of optically contacted Fabry-Perot etalons. A photoelectric raster scan of the etalon transmission intensity distribution is performed at each of three closely spaced etalon tunings, one at maximum on-axis and two at the half-maxima on-axis positions. Simple data manipulation gives numerical or contour maps of the parallelism defect. Results demonstrating the effect of mechanical constraints on etalon parallelism are presented.