This chapter describes the uses of diffractive optics in lens design. In some applications an optical component may require a diffractive surface combined with a classic lens element. In other cases the requirements can be satisfied with just a diffractive element. Both types are described and analyzed here. After describing the concepts and approaches used to design a classic lens, we demonstrate how they can be applied to a single diffractive lens. The use of diffractive surfaces in hybrid lenses to correct chromatic aberration is also described. In Chapter 10, the use of diffractive optics in lens design is extended to multielement systems and to their use in thermal compensation of lenses.
The lens design process is depicted in Fig. 4.1. After determining the specifications of the optical system, a starting lens design is evaluated by entering its description in a lens design program. The specifications of the performance of the component as a linear set of weighted target values, called a merit function, are set. Then some of the parameters of the optical system are varied and the merit function is evaluated. As the actual parameters approach the desired values, the merit function will approach zero. After a number of iterations, the design has improved (optimized) in comparison with the starting point. It is up to the designer to determine if the performance is good enough for the desired application or if some design changes need to be made, with additional optimization steps.
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