Bulk Saturable absorption in Topological Insulator thin Films

TL;DR

This paper investigates the nonlinear optical absorption of Bi2Se3 topological insulator thin films, revealing enhanced saturable absorption primarily originating from bulk states through specific experimental design.

Contribution

It demonstrates significantly improved saturable absorption in TI thin films and clarifies that the bulk states are responsible for this property, unlike previous inconclusive results.

Findings

Saturable intensity improved by an order of magnitude

Bulk states are the main source of saturable absorption

Experimental design distinguishes surface vs. bulk contributions

Abstract

We present nonlinear optical absorption properties of pulsed laser deposited thin films of topological insulator (TI), Bi2Se3 on quartz substrate, using open aperture Z - scan technique. The saturable intensity of as-deposited thin films has been found remarkably improved by an order of magnitude compared to the values reported earlier in the literature. Past results from the literature are inconclusive in establishing whether the saturable absorption is coming from surface states or the bulk. Specifically designed experiments with magnetically doped TI samples allow us to attribute the saturable absorption characteristic of TI to the bulk states. Detailed experimental procedures and possible explanation of observed results have been discussed.