Chromatic interferometry with small frequency differences

TL;DR

This paper introduces a novel two-crystal method for chromatic interferometry that enables interference measurements with photons having frequency differences outside traditional passbands, demonstrated experimentally with a 200 GHz difference.

Contribution

The paper presents a new two-crystal technique for color erasure, expanding chromatic interferometry to wider frequency differences beyond existing crystal passbands.

Findings

Successful experimental demonstration with 1064.4 nm and 1063.6 nm sources

Interference observed with a 200 GHz frequency difference

Broadens applicability of chromatic interferometry techniques

Abstract

By developing a `two-crystal' method for color erasure, we can broaden the scope of chromatic interferometry to include optical photons whose frequency difference falls outside of the 400 nm to 4500 nm wavelength range, which is the passband of a PPLN crystal. We demonstrate this possibility experimentally, by observing interference patterns between sources at 1064.4 nm and 1063.6 nm, corresponding to a frequency difference of about 200 GHz.