Use Of The Smartt Interferometer As An Alignment Tool For Infrared Laser Systems

The ability to minimize the pointing and focusing errors at the focal plane is crucial in many applications involving infrared laser systems. This is particularly the case for systems involving multiple beams reaching the focal plane, as in the case of the LASL CO2 laser fusion systems. For example, the LASL Helios CO2 Laser Fusion System has eight 34-cm diameter beams each with an f number of approximately 2.4 coming to focus, the last element being an off-aperture parabola with a focal length of approximately 77.3 cm. The design tolerance for pointing accuracy is ± 25 microns and for focusing accuracy is ± 50 microns for the Helios system. The Smartt interferometer shows promise of not only evaluating the optical quality of the beam, but it can be used to align the beam to the tolerance levels stated above. This paper describes the procedure, as well as experimental results obtained, which show that pointing accuracies of ±12.5 microns and focusing accuracies of ±25 microns are obtained at the focus of a CO2 laser beam in a setup which duplicates the target region of the Helios CO2 Laser Fusion System. The backlash in the x-y-z stage micrometer used in the experiment is estimated to be 10 microns, though precautions were taken to move in the same direction throughout an experimental run.