Resonance-enhanced spectral funneling in Fabry-Perot resonators with a temporal boundary mirror

TL;DR

This paper demonstrates a novel method for spectral funneling of terahertz light using a Fabry-Perot resonator with a temporal boundary, achieving high efficiency through abrupt changes in mirror reflectance.

Contribution

It introduces a new approach to spectral redistribution in THz frequencies via temporal boundary manipulation in a Fabry-Perot resonator, enhancing spectral funneling efficiency.

Findings

Achieved up to 33% energy funneling efficiency into the fundamental mode.

Demonstrated spectral broadening of THz pulses due to temporal boundary effects.

Resonance enhancement facilitated by sudden Q-factor change from 4.8 to 48.

Abstract

A temporal boundary refers to a specific time at which the properties of an optical medium are abruptly changed. When light interacts with the temporal boundary, its spectral content can be redistributed due to the breaking of continuous time-translational symmetry of the medium where light resides. In this work, we use this principle to demonstrate, at terahertz (THz) frequencies, the resonance-enhanced spectral funneling of light coupled to a Fabry-Perot resonator with a temporal boundary mirror. To produce a temporal boundary effect, we abruptly increase the reflectance of a mirror constituting the Fabry-Perot resonator and, correspondingly, its quality factor in a step-like manner. The abrupt increase in the mirror reflectance leads to a trimming of the coupled THz pulse that causes the pulse to broaden in the spectral domain. Through this dynamic resonant process, the spectral contents of the input THz pulse are redistributed into the modal frequencies of the high-Q Fabry-Perot resonator formed after the temporal boundary. An energy conversion efficiency of up to 33% was recorded for funneling into the fundamental mode with a Fabry-Perot resonator exhibiting a sudden Q-factor change from 4.8 to 48. We anticipate that the proposed resonance-enhanced spectral funneling technique could be further utilized in the development of efficient mechanically tunable narrowband terahertz sources for diverse applications.