Optimal photon-pair single mode coupling in narrow-band spontaneous parametric down-conversion with arbitrary pump profile

TL;DR

This paper presents a flexible theoretical framework for optimizing single-mode photon-pair sources in narrow-band spontaneous parametric down-conversion, focusing on performance metrics like brightness and efficiency, validated by experimental results.

Contribution

It introduces a general, assumption-minimized theory for optimizing photon-pair coupling in SPDC sources, adaptable to various experimental configurations.

Findings

Optimized configurations improve brightness and efficiency.

Theoretical predictions match experimental optimization results.

Guidelines for experimental setup design are provided.

Abstract

A theoretical study of the performance of single-mode coupled spontaneous parametric downconversion sources is proposed, which only requires very few assumptions of practical interest : narrow-bandwidth and quasi-degenerate collinear generation. Other assumptions like pump beam spatial and temporal envelopes, target single-mode profile and size, and non-linear susceptibility distribution, are only taken into account in the final step of the computation, thus making the theory general and flexible. Figures of merit for performance include absolute collected brightness, pair collection efficiency and heralding ratio. The optimization of these values is investigated through functions that only depend on dimensionless parameters, allowing for deducing from the results the best experimental configuration for a whole range of design choices (e.g. crystal length, pump power). A particular application of the theory is validated by an experimental optimization obtained under compatible assumptions. A comparison with other works and proposals for numerically implementing the theory in its most generality are also provided.