Grazing incidence interferometry: the use of the Linnik interferometer for testing image-forming reflection systems

Fourier transform interferometer alignment method

A rapid and convenient method has been developed to facilitate the alignment of the image-plane components of point-diffraction interferometers, including the phase-shifting point-diffraction interferometer. In real time, the Fourier transform of the detected image is used to calculate a pseudoimage of the electric field in the image plane of the test optic where thecritical alignment o f variousoptical components is performed. Reconstruction of the pseudoimage is similar to off-axis, Fourier transform holography. Intermediate steps in the alignment procedure are described. Fine alignment is aided by the introduction and optimization of a global-contrast parameter that is easily calculated from the Fourier transform. Additional applications include the alignment of image-plane apertures in general optical systems, the rapid identification of patterned image-plane alignment marks, and the probing of important image-plane field properties.

Application of a Shack cube as a beam splitter in interferometers with a local reference beam

A different setup of the Mach-Zehnder interferometer for testing the convergent wave front is described. A Shack cube is used to replace a traditional recollimator and a parallel-plate beam splitter. An equivalent pupil model has been suggested that describes the point diffraction mechanism. The calibration procedures for the Mach-Zehnder interferometer are described. The Shack-cube beam splitter has the advantages of compactness and better reference-beam quality compared with the recollimator and the parallel-plate beam splitter.

Liquid-crystal point-diffraction interferometer for wave-front measurements

A new instrument, the liquid-crystal point-diffraction interferometer (LCPDI), is developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point-diffraction interferometer and adds to it a phase-stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave fronts with very high data density and with automated data reduction. We describe the theory and design of the LCPDI. A focus shift was measured with the LCPDI, and the results are compared with theoretical results.

Fizeau digital interferometry with a diffraction-generated spherical wave for testing focusing optics

A sufficiently small, reflective spherical particle at the focus of a test lens can replace the spherical autostigmatizing mirror in Fizeau digital interferometry, which is used for testing focusing optics. This small particle serves as a secondary coherent point source in the test arm and generates by diffraction a spherical wave that is used to produce the test beam. The relationships between the diffraction-generated wave and the size and shape of the diffracting element are discussed and also used to properly select the diffracting element. Experimental results confirm that the new technique has high accuracy.