Dual Measurements of Temporal and Spatial Coherence of Light in a Single Experimental Setup using a Modified Michelson Interferometer

TL;DR

This paper presents a modified Michelson interferometer capable of simultaneously measuring the temporal and spatial coherence of light sources, offering improved accuracy and practicality over traditional methods especially for low-coherence sources.

Contribution

The authors introduce a novel interferometric setup that combines spatial and temporal coherence measurements in a single system, addressing prior limitations and reducing systematic errors.

Findings

Enables dual measurement of spatial and temporal coherence in a single setup

Reduces systematic errors compared to standard plane mirror interferometers

Extends measurement range without sacrificing precision

Abstract

An experimental technique is developed to simultaneously measure both temporal and spatial coherences of a light source by altering a standard Michelson interferometer, which has been primarily used for measuring temporal coherence only. Instead of using simple plane mirrors, two retroreflectors and their longitudinal and lateral movements are utilized to incorporate spatial coherence measurement using this modified Michelson interferometer. In general, one uses Young double slit interferometer to measure spatial coherence. However, this modified interferometer can be used as an optical setup kept at room temperature outside a cryostat to measure spatio-temporal coherence of a light source placed at cryogenic temperatures. This avoids the added complexities of modulation of interference fringe patterns due to single slit diffraction as well. The process of mixing of spatial and temporal parts of coherences is intrinsic to existing methods for dual measurements. We addressed these issues of spatiotemporal mixing and we introduced a method of temporal filtering in spatial coherence measurements. We also developed a curve overlap method which is used to extend the range of the experimental setup during temporal coherence measurements without compromising the precision. Together, these methods provide major advantages over plane mirror based standard interferometric systems for dual measurements in avoiding systematic errors which lead to inaccuracies especially for light sources with low coherences.