Compensation for Anamorphotic Distortion in Grazing-Incidence Interferometry Testing Planar Specimens

One important feature of grazing-incidence interferometry is the anamorphotic distortion or the foreshortened view of the interference pattern along the optical axis caused by the geometry of the interferometer. To compensate for the consequential lower resolution along the optical axis, a setup was built in which the object plane is imaged onto a rectifying grating, ensuring sharp mapping of the whole specimen onto the detector. A volume hologram and a diffraction grating serve as rectifying elements and are applied to measure various types of planar objects such as mirrors and structured plastic samples. Accuracy, image sharpness, and residual distortion for both cases are discussed.