Multiple beam Fizeau interferometer with frequency comb illumination

Real wedge interferometers of the Fizeau-type do not allow for fringes in case of a spectral broad band source. Here, the use of a suitable frequency comb source will help to overcome this limitation on the one hand and on the other will offer the capability for enhanced phase sensitivity in high precision measurements of surface deviations. Frequency combs can be produced e.g. by passive filtering of the light emitted by a broad band source as a superlum-diode. White light fringes can serve as an indication for the correct choice of multiplication factors in superposition interferometry. Here, we will discuss the application of spatially incoherent broad band light frequency filtered through a Fabry-Perot filter. The main applications are: (1) surface profiling using two-beam Fizeau interferometers, (2) selection of single cavities out of a series of interlaced cavities, and (3) sensitivity enhancement for multi-beam interferometers for planeness measurements. Repeatabilities in the sub-Å-range rms can be achieved.