The polychromatic integral diffraction
efficiency (PIDE) metric is
generally used to select the most suitable materials for multilayer
diffractive optical elements (MLDOEs). However, this method is based
on the thin element approximation, which yields inaccurate results in
the case of thick diffractive elements such as MLDOEs. We propose a
new material selection approach, to the best of our knowledge, based
on three metrics: transmission, total internal reflection, and the
optical component’s total thickness. This approach, called “geometric
optics material selection method” (GO-MSM), is tested in mid-wave and
long-wave infrared bands. Finite-difference time-domain is used to
study the optical performance (Strehl ratio) of the “optimal” MLDOE
combinations obtained with the PIDE metric and the GO-MSM. Only the
proposed method can provide MLDOE designs that perform. This study
also shows that an MLDOE gap filled with a low index material (air)
strongly degrades the image quality.