PT-symmetric laser-absorber

TL;DR

This paper demonstrates that a parity-time symmetric optical medium can function simultaneously as a laser and a coherent perfect absorber, creating a device that can emit or fully absorb coherent waves depending on the conditions.

Contribution

It introduces the concept of a PT-symmetric CPA-laser, showing that such a device can act as both a laser oscillator and a perfect absorber under certain conditions.

Findings

PT-symmetric media can serve as both lasers and perfect absorbers

The device's behavior depends on the amplitude and phase of incoming waves

Theoretical analysis of amplification and absorption below lasing threshold

Abstract

In a recent work, Y.D. Chong et al. [Phys. Rev. Lett. {\bf 105}, 053901 (2010)] proposed the idea of a coherent perfect absorber (CPA) as the time-reversed counterpart of a laser, in which a purely incoming radiation pattern is completely absorbed by a lossy medium. The optical medium that realizes CPA is obtained by reversing the gain with absorption, and thus it generally differs from the lasing medium. Here it is shown that a laser with an optical medium that satisfies the parity-time $(\mathcal{PT})$ symmetry condition $\epsilon(-\mathbf{r})=\epsilon^*(\mathbf{r})$ for the dielectric constant behaves simultaneously as a laser oscillator (i.e. it can emit outgoing coherent waves) and as a CPA (i.e. it can fully absorb incoming coherent waves with appropriate amplitudes and phases). Such a device can be thus referred to as a $\mathcal{PT}$-symmetric CPA-laser. The general amplification/absorption features of the $\mathcal{PT}$ CPA-laser below lasing threshold driven by two fields are determined.