Externally triggered coherent two-photon emission from hydrogen molecules

TL;DR

This paper demonstrates a significant enhancement of two-photon emission from excited hydrogen molecules triggered by externally injected mid-infrared pulses, allowing better control and understanding of the emission mechanism.

Contribution

It introduces the use of external mid-infrared pulses to control two-photon emission, achieving a much higher enhancement factor than previous internally triggered methods.

Findings

Emission spectrum depends on trigger pulse energy and timing

Number of emitted photons reaches 6×10^11 per pulse

Enhancement factor exceeds 10^18, three orders of magnitude higher than previous results

Abstract

We report coherent enhancement of two-photon emission from the excited vibrational state of molecular hydrogen triggered by irradiating mid-infrared pulses externally. We previously observed the two-photon emission triggered by the internally generated fourth Stokes photons. By injecting independent mid-infrared pulses externally, it is possible to control experimental parameters and investigate the mechanism in more detail. In this article, we describe the two-photon emission using the external trigger pulses. Its spectrum and dependence on the energy and timing of the trigger pulse are presented along with numerical simulations based on the Maxwell-Bloch equations. The measured number of emitted photons is 6 10^11 photons/pulse and the resulting enhancement factor from the spontaneous emission is more than 10^18. This value is three orders of magnitude higher than that of the previous experiment. External control of emission process is expected to be essential for observation of weaker process of radiative emission of neutrino pair.