High NA Fizeau Phase Shifting Interferometry

Axial actuation of the transmission sphere (TS) for Phase Shifting Interferometry (PSI) in spherical Fizeau cavities causes phase shifts varying as cos(aperture angle). This variation eps should remain within 1:0.67 for simple PSI algorithms, usually limiting Fizeau-PSI to NA≤5(f#≥0.67). Advanced algorithms and a modified shift range of 1.5:0.5 (effectively 3:1) make Fizeau-PSI feasible up to NA≈0.94 (f#≈0.53). For even larger variations up to 5:1 (NA≤0.98) we propose a concurrent zonal analysis to avoid the reduced fringe contrast of more advanced PSI algorithms at high ε. At high NA, always present residual defocus causes apparent higher order spherical aberrations, not handled correctly by the usual power-removal in conventional software. For an ideal interferometer and TS these can be computed from the measured defocus and removed. Alternatively, their defocus-dependence may be calibrated for a particular TS setup. We present absolute results (using N angular positions and "catseye") for a NA=0.94 TS as well as results on semispherical concave mirrors. The latter are compared to data obtained on a Twyman-Green setup and high NA dry microscope objectives (NA≤0.95).