The great wedge: Quantifying chromatic aberration in imaging spectroscopy systems and application to temperature measurements in the laser-heated diamond anvil cell

Abstract

To aid in evaluating spatial and spectral imaging abilities of any imaging spectroradiometer system, we developed a spectral intensity gradient standard based on the behavior of a birefringent wedge imaged between cross polarizers. By comparing calculated with observed images of the wedge, a chromatic scrambling kernel was measured to generally estimate chromatic aberrations in any spectral imaging optical system. This technique provides a quantitative method to compare spectral imaging quality of different optical systems and also provides a quick test for severe misalignments in the optical path. Applying this method to the spectroradiometric measurement of temperature and temperature gradients in the laser-heated diamond cell, the observed scrambling kernel is used to infer original hotspot information from measured behavior, to provide a quantitative evaluation of the ability to measure a temperature gradient in any spectral system, and to yield an objective determination of precision of spectroradiometric temperature measurements. The birefringent wedge method and its application described in this paper are simple and inexpensive enough to be used on any spectroradiometric system.