Angular-spectrum-dependent interference

TL;DR

This paper introduces a novel optical interference phenomenon using photons with structured frequency-angular spectra, resulting in fringes that vary more rapidly with optical path difference, potentially enhancing interferometry sensitivity.

Contribution

The study experimentally validates a new interference effect involving structured photon spectra, expanding understanding and potential applications in high-sensitivity interferometry.

Findings

Interference fringes vary more rapidly with OPD for structured spectra.

Equivalent wavelength of 29.38 nm demonstrates enhanced resolution.

Phenomenon validated experimentally with nonlinear crystal source.

Abstract

Optical interference is not only a fundamental phenomenon that has enabled new theories of light to be derived but it has also been used in interferometry for the measurement of small displacements, refractive index changes and surface irregularities. In a two-beam interferometer, variations in the interference fringes are used as a diagnostic for anything that causes the optical path difference (OPD) to change; therefore, for a specified OPD, greater variation in the fringes indicates better measurement sensitivity. Here, we introduce and experimentally validate an interesting optical interference phenomenon that uses photons with a structured frequency-angular spectrum, which are generated from a spontaneous parametric down-conversion process in a nonlinear crystal. This interference phenomenon is manifested as interference fringes that vary much more rapidly with increasing OPD than the corresponding fringes for equal-inclination interference; the phenomenon is parameterised using an equivalent wavelength, which under our experimental conditions is 29.38 nm or about 1/27 of the real wavelength. This phenomenon not only enriches the knowledge with regard to optical interference but also offers promise for applications in interferometry.