The design and evaluation of an athermal laser beam expander

Abstract

A systematic design procedure for a laser beam expander is given in which special emphasis is placed on the athermalization process during the predesign stage. Initially the aberration theory, as well as the theory of athermalization and a functional model for simulating a Nd-Yag laser are presented. These theories are consequently used in the design of the beam expander. The design process starts off by translating the user requirements into optical design specifications. These specifications were used as a basis for the design of a two lens athermalized system which was corrected for aberrations. Unfortunately, the resultant design could not entirely meet the user requirements, and a more complex design was indicated. A three-lens system was then assumed which required a completely new approach to athermalization and aberration correction. Four equations, expressing magnification, total length, afocality and atermalization were simultaneously solved and gave a first order layout. The aberrations were then minimized and the final design realized. The final design was evaluated and the results compared with specifications. For the analysis the expected radiation pattern of the complete laser/beam expander system was constructed and the relationship between the uniformity of the radiation pattern and the exit pupil diameter was established. The analysis shows conclusively that the design is optimal and that it satisfies all user requirements.