Optical switching and bistability in a four-level atomic systems

TL;DR

This paper investigates how coherent control of nonlinear absorption in four-level atomic systems can enable optical switching and bistability, with potential applications in optical information processing.

Contribution

It demonstrates how control fields can modulate absorption and bistability in four-level atomic systems, introducing new methods for optical switching and nonlinear absorption control.

Findings

Large absorption peaks enable optical switching.

Control fields can modify the threshold of optical bistability.

Achieved saturable and reverse saturable absorption using simple atomic systems.

Abstract

We explore the coherent control of nonlinear absorption of intense laser fields in four-level atomic systems. For instance, in a four-level ladder system, a coupling field creates electromagnetically induced transparency (EIT) with Aulter-Townes doublet for the probe field while the control field is absent. A large absorption peak appears at resonance as the control field is switched on. We show how such a large absorption leads to optical switching. Further, this large absorption gets diminished and a transparency window appears due to the saturation effects as the strength of the probe field is increased. We further demonstrate that the threshold of the optical bistability can be modified by suitable choices of the coupling and the control fields. In a four-level Y-type configuration, the effect of the control field on saturable absorption (SA) and reverse saturable absorption (RSA) is highlighted in the context of nonlinear absorption of the probe field. We achieve RSA and SA in a simple atomic system just by applying a control field.