Interferometric test of optical systems: effects of probe beam collimation errors

The effects of probe beam residual power in interferometry are investigated. It is seem thwt residual power produces an asymmetry between the forward and backward beams that is scaled with f2# i.e., the effect can be easily seen in very slow optical systems. Common methods to detect residual power are discussed, showing the effectiveness of lateral shear interferometry to carefully set the collimation of the probe beam. A device approaching the order of manitude established by Ray-leigh's quarter wavelength rule is demonstrated.