Some applications of the gas laser as a source of light for the testing of optical systems

Recently one of the authors has described a simple lateral shearing interferometer. This consists of a single nearly parallel plate of glass and when used in conjunction with a gas laser source forms a simple and stable lateral shearing interferometer. The amount of shear is variable by changing the angle of incidence on the glass plate. This has been used to set up a test procedure for large optical systems (especially large mirrors). A procedure is given for calculating the wavefront from the shearing pattern. Certain problems associated with the use of a gas laser are discussed. In the optical testing applications, it is necessary to control the spatial coherence of the laser independently and a simple method to achieve this objective is described