Frequency-selective time-resolved phonon spectroscopy using fluorescence line narrowing

Abstract

We report on a new method, based on fluorescence line narrowing, for studying nonequilibrium acoustic phonons in a frequency-selective way. High-resolution phonon detection is achieved by exciting ruby directly into a homogeneous packet of the E ( 2E) metastable state, and analyzing the enhanced R 2 luminescence following absorption of phonons in the transition from E ( 2E) to 2 A ( 2E). In the present experiment, a flat spectrum phonons is injected with heat pulses of 100 ns duration. The phonon spectrum observed initially exhibits a dip, reflecting the absorption of resonant phonons. Following the heat pulse, the phonons escape with a rate increasing with the distance from resonance. The experiments suggest conversion of ballistic phonons as well as of bottlenecked phonons in the wings into resonant ones.