A compact zoom system originating from a generalized form of the Alvarez-Lohmann (AL) varifocal lens concept is developed and discussed here in terms of its potential future applications in infrared imagers. Design methodology based on the use of different polynomial representations of corresponding freeform surfaces is also briefly outlined. In particular, a targeted polynomial technique, which can reduce the dimensionality of the optimization task, is put forward. Silicon-based AL zoom solution is found especially attractive: it can work in both in MWIR band and quasimonochromatic SWIR channel. Complex freeform surfaces can be generated in Silicon substrates by using dedicated SPDT processes. As a design example, a 3x MWIR/SWIR afocal Galilean freeform zoom is presented which covers a FOV range from 7.4° to 22.5° and offers close to diffraction limited performance.
S. Szapiel and C. Greenhalgh, "Freeform based lateral-shift compact zoom system: theory and computer simulations," Proc. SPIE 10627, Advanced Optics for Defense Applications: UV through LWIR III, 1062707 (Presented at SPIE Defense + Security: April 15, 2018; Published: 8 May 2018); https://doi.org/10.1117/12.2309815.
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