Optically unstable phase from ion-ion interactions in an erbium doped crystal

TL;DR

This paper reports the discovery of an optically unstable phase in an erbium-doped crystal caused by ion-ion interactions, leading to dynamic light instability under strong laser illumination, modeled with a many-body Bloch-equation framework.

Contribution

It introduces the observation of optical instability in erbium ions due to ion-ion interactions and develops a Bloch-equation model including excitation-induced frequency shifts.

Findings

Dynamic instability observed in transmitted light

Transient net gain with double pass through the sample

Ion-ion interactions cause the instability

Abstract

We demonstrate an optical unstable phase for a laser driven erbium ion ensemble. The transmitted light through an erbium-doped yttrium orthosillicate crystal becomes dynamically unstable when illuminated by a strong continuous-wave laser. Transient net gain was recorded if the light passes the sample twice. The experimental results are understood in the framework of a many-body system interacting with a classical field, where the ion-ion interaction becomes significant as a result of the high erbium concentration. A Bloch-equation model that includes the excitation-induced frequency-shift is introduced to discuss the conditions of the instabilities.