Direct determination of 2D momentum space from 2D spatial coherence of light using a modified Michelson interferometer

Abstract

Momentum space distribution of photons coming out of any light emitting material/device provides critical information about their underlying physical origin. Conventional methods of determining such properties impose specific instrumentational difficulties for probing samples kept within a low temperature cryostat. There were past studies to measure a one-dimensional coherence function, which could then be used for extracting momentum space information, as well as reports of measurements of just a two-dimensional (2D) coherence function. However, all of those are associated with additional experimental complexities. So, here we propose a simpler, modified Michelson interferometer based optical setup that is kept at room temperature and placed outside the low temperature cryostat at a distance away from it. We initially measure the 2D coherence function of emitted light, which can then be used to directly estimate the 2D in-plane momentum space distribution by calculating its fast Fourier transform. We also discuss how this experimental method can overcome instrumentational difficulties encountered in the past. Similar instrumentations can also be extended for momentum space resolved astronomical studies and telecommunications involving distant light sources.