Interferometric focal length measurement of positive and negative lenses using a lateral-shearing cyclic path optical configuration setup and polarization phase-shifting interferometry.

We present a simple interferometric focal length measurement technique for measuring the focal length of positive and negative lenses using a lateral-shearing cyclic path optical configuration (CPOC) setup and polarization phase-shifting interferometry (PPSI). The technique requires an auxiliary lens, whose focal length need not be known accurately, for generating a focused point source at its focal plane. The focal point of the test lens is adjusted to be in the vicinity of the focus of the auxiliary lens. The radii of the resulting spherical wave fronts emerging from the test lens, due to the defocus, for two different longitudinal shifted positions of the test lens are measured using the lateral-shearing CPOC setup and PPSI. Focal length of the test lens is determined from the known longitudinal shift and from the measured radii of the spherical wave fronts. Results obtained for 200.0 mm convex and 100.0 mm concave test lenses are presented.

Measurement of surface form error of an optical surface with reduced interferometric spatial coherence artifacts using a ring source and polarization phase-shifting interferometry.

We present a technique for the measurement of surface form error of an optical surface using a ring source and polarization phase-shifting interferometry (PPSI). The ring source, generated using a refracting axicon, is projected onto a rotating diffuser to reduce the spatial coherence noise generated by the spatially coherent He-Ne laser and to enhance the interference fringe contrast. PPSI is applied to extract the phase [and hence the optical path difference (OPD)] from the interference fringes formed by a Fizeau cavity using the ring source. The OPD values are least-square fitted to a plane and the surface form errors are evaluated from the deviations of the OPD values from the fitted reference plane. A two-step subtraction method to reduce the system errors and the effect of the ring source diameter on the effective measurement area of the test surface are discussed. The main advantage of the technique is that the perturbations in the Fizeau cavity are negligible during the phase shifts as the phase shifts between the interfering beams are introduced outside the cavity.

Small roll angle measurement using lateral shearing cyclic path polarization interferometry.

We present a technique for the measurement of roll angular displacement of a rotary stage using a lateral shearing cyclic path optical configuration (CPOC) setup and polarization phase shifting interferometry (PPSI). The CPOC setup, aligned on the rotary stage, laterally shears the input plane polarized spherical beam into a pair of orthogonally polarized beams, which when brought to the same state of polarization by a polarizer produce interference fringes similar to Young's fringes. Rotation of the CPOC setup in its plane introduces a phase change between the orthogonally polarized lateral sheared beams due to the change in angle of incidence of the input beam. The change in the phase results in spatial displacement of the interference fringes. Using PPSI, the phase, or the optical path difference change between the laterally sheared beams that is related to the rotation angle of the CPOC setup, is measured.