Giant Narrowband Twin-Beam Generation along the Pump Energy Propagation

TL;DR

This paper demonstrates how to overcome walk-off effects in high-gain parametric down-conversion to enhance ultrafast twin-beam generation, enabling more efficient quantum light sources.

Contribution

It introduces a method to utilize walk-off effects constructively in high-gain PDC, improving twin-beam emission along the pump propagation direction.

Findings

Enhanced twin-beam generation along pump direction

Narrowed angular and frequency spectra of twin beams

Potential for ultrafast twin photon sources

Abstract

Walk-off effects, originating from the difference between the group and phase velocities, limit the efficiency of nonlinear optical interactions. While transverse walk-off can be eliminated by proper medium engineering, longitudinal walk-off is harder to avoid. In particular, ultrafast twin- beam generation via pulsed parametric down-conversion (PDC) and four-wave mixing (FWM) is only possible in short crystals or fibres or in double-path schemes. Here we show that in high-gain PDC, one can overcome the destructive role of both effects and even turn them into useful tools for shaping the emission. In our experiment, one of the twin beams is emitted along the pump Poynting vector or its group velocity matches that of the pump. The result is dramatically enhanced generation of both twin beams, with the simultaneous narrowing of angular and frequency spectrum. The effect will enable efficient generation of ultrafast twin photons and beams in cavities, waveguides, and whispering-gallery mode resonators.