Virtual single-photon transition interrupted: time-gated optical gain and loss

TL;DR

This paper demonstrates that the temporal evolution of virtual single-photon transitions can be mapped using a second pulsed field, revealing controllable optical gain and loss, with potential applications in laser development and accessing new spectral regions.

Contribution

It introduces a novel method to map virtual single-photon transition dynamics using time-gated optical signals controlled by pulse delay.

Findings

Observation of optical gain and loss in virtual transitions

Qualitative agreement with transient absorption spectroscopy in helium

Potential for new laser schemes and spectral access

Abstract

The response of matter to an optical excitation consists essentially of absorption and emission. Traditional spectroscopy accesses the frequency-resolved and time-integrated response, while the temporal evolution stays concealed. However, we will demonstrate here that the temporal evolution of a virtual single-photon transition can be mapped out by a second pulsed electromagnetic field. The resulting optical signal shows previously unexpected optical gain and loss, which can be gated and controlled via the relative delay of the electromagnetic fields. The model presented here can be applied to any system that assumes a two-level character through near-resonant optical dipole excitation, whether they are of atomic, molecular or even solid-state nature. These theoretical observations are in excellent qualitative agreement with our transient absorption spectroscopy study in helium. The presented results can act as starting point for a new scheme for creating optical gain, which is a prerequisite for the operation of lasers. It may be possible to open the doors to spectral regions, which were difficult to access until now, e.g. in the extreme ultraviolet.