Achromatslenses

A thin achromat can be corrected for third-order spherical aberration, coma, and axial chromatic aberration. The combination consists of a positive and a negative element. To eliminate axial chromatic aberration, a simple relation between powers and Abbe numbers of the two elements must be met. This relation is

These choices are a sound starting point that lead quickly to good solutions in terms of optimization with the computer after adding thicknesses and spacings.

Achromatsmeaning

Spectral regionMWIR(3 – 5 μm)LWIR(8 – 12 μm)Front elementSiliconAmtir-1R10.97f1fR23.25f6fRear elementGermaniumZinc sulfideR34f−6fR42f−24f

Achromatsfor sale

The process of deriving the complete prescription for such a doublet is straightforward but too cumbersome to be included here.1

The radii as a factor of an achromat’s focal length are listed in the table below for two objectives: one for the MWIR and one for the LWIR region. For the MWIR lens, silicon and germanium have been the materials chosen, and the combination Amtir-1/zinc sulfide was selected for the LWIR objective. Amtir is an acronym for amorphous material transmitting infrared radiation. The composition of Amtir-1 is 33% Ge, 12% As, and 55% Se.