Absolute measurement of aspheric lens with electrically tunable lens in digital holography

A novel method for testing aspheric lenses using digital holography with an electrically tunable lens (ETL) is proposed and experimentally verified. The ETL generates a tunable deformed wavefront which helps to decrease the high gradient of aspheric lenses. By decomposing the aspheric surface into two resolvable ones, its absolute phase can be determined using a double-exposure measurement. In this method, the wavefront generated by the ETL need not be identical to the aspheric surface as in conventional null interferometer system, but just sufficient to resolve the high gradient surface. On the other hand, the tunability of the ETL allows generation of wavefronts which can be used to test different aspheric lens. Furthermore, advantages of the ETL such as low cost, fast response, and compact configuration make the proposed method a promising technique for aspheric surface measurement.