The thick-crystal regime in photon pair sources

TL;DR

This paper investigates the thick-crystal regime in photon pair sources, demonstrating high collection efficiency and brightness with a single Barium Borate crystal, and analyzing how crystal length and mode affect performance.

Contribution

It provides comprehensive measurement data and insights into how the effective interaction length and crystal parameters influence photon pair source efficiency.

Findings

Achieved 89% collection efficiency with a single crystal.

Longer crystals with increased walk-off do not reduce efficiency.

Collection mode dominates the effective interaction length.

Abstract

We present comprehensive measurement data on the pump and collection beam parameters necessary to achieve high collection efficiency ($89.0 \pm 1.7 \%$) together with high brightness when a single $\beta$-Barium Borate crystal is operated in the thick-crystal regime and pumped with a narrow linewidth laser source. Spectral analysis of the collinear, non-degenerate photons suggest that the effective interaction length within the crystal is dominated by the collection beam mode and the use of longer crystals with increased spatial walk-off does not necessarily lead to a reduced collection efficiency. This result is an important consideration for optical designers who seek to develop practical photon pair sources.