Interferometric Tests for Micro-Optics

Micro-optics comprises different kinds of optical elements. This paper will mainly deal with the testing of microlenses, not of mirrors, prisms and other microoptical devices. Microlenses can be classified into two types: refractive and diffractive lenses. Since the diffractive lenses are normally computer generated it is not necessary to test their global optical function, only the microstructure has to be measured. In the case of refractive microlenses there are several properties which have to be determined: paraxial parameters (e.g. focal length, diameter), surface quality (deviations from the ideal form) and wave aberrations. The measurement of these parameters with the help of interferometers in reflected and transmitted light, as well as the advantages and problems of these interferometers, will be discussed.