Null lenses design for small aspherical surface with large NA

摘要

To test the small aspherical mold surface with large NA, we develop a kind of null lens system which is made up of four thin lenses, the first two thin lenses form a system with small NA which is mainly used to produce positive spherical aberation; the other two thin lens form a large NA system which offers negative spherical aberration; the latter together with that of the front two elements meets the null testing need. The wave front variation of testing system due to the manufacture & test & assembly and adjustments error is analyzed, by this analyses, we know that we are capable of measuring the aspherical surface to the accuracy of 0.05 lambda, it is enough to satisfy the testing of mold surface of compact disc object lenses.