Progress with a Determination of the Speed of Light

Abstract

Interferometric comparison of the carbon dioxide laser wavelength with the primary standard in the visible presents a number of special problems arising from the large wavelength difference. The first of these is the photodetector problem. The use of separate detectors means that particular attention must be paid to their uniformity of response for lateral and angular position variations. There are few materials with transmission properties in both spectral regions, and they are not readily available in the necessary quality and sizes. The use of separate components for the two radiations may thus be considered, such as variable path interferometers with the optics for the two radiations arranged coaxially or back to back. Such systems require stricter attention to stability and adjustment tolerances than do systems having common optical paths.