Design, fabrication and characterization of glass phase steps for application in phase shifting interferometry

In this paper, we report on the design and fabrication of a low-cost phase shifter for application in phase shifting interferometry. Phase shifting interferometry is a powerful method for surface characterization. It uses interference data recorded during a series of predetermined phase shifts to recover the induced phase by the object surface. These controlled phase shifts are typically performed by putting a piezo-electric ceramic behind one of interferometer mirrors. Applying the controlled voltage to this ceramic provides the desired phase shifts. The piezo-electric positioners are very expensive. Phase shifting interferometry has different algorithms. One of the most effective algorithms is the four step phase shifting interferometry. In this algorithm, four interferograms are taken; then the unknown phase term due to surface is extracted by combining these interferograms. Here, we have proposed a low-cost alternative for piezo-electric positioners. Firstly, using the Fresnel diffraction from the phase step, we have measured etch rate of glass by HF acid. Then, a phase step with a quarter wavelength phase shift has been fabricated on a glass plate. The step height has been measured using Fresnel diffraction (phase step diffractometer) and interferometry. Then a stepwise structure has been fabricated on glass, providing phase shifts needed in the four step phase shifting interferometry.