Testing the coma of decentration with a confocal Fabry-Perot interferometer

The use of a confocal Fabry-Perot interferometer for testing asymmetrical wavefronts is considered. This is the inverting-type interferometer which can be used for investigation of the asymmetry of wavefront aberrations of an optical system. The aberrated wavefront interferes with the wave inverted in the interferometer and only the effect of the nonsymmetrical aberration can be observed in the fringe pattern. For an axial wavefront the coma of decentration is detected. The influence of alignment errors of the interferometer, including the lateral shear and confocal error, on the accuracy of the method is considered. The advantage of the method proposed in comparison with a reversal-type interferometer is that the detected aberration value is independent of the azimuth of decentration with respect to the interferometer.