Two-dimensional WSe2 flakes under high power optical excitation

Kirill A Brekhov,Sergey D Lavrov,Nikita A Ilyin,Andrey V Kudryavtsev

doi:10.3897/j.moem.7.3.74274

Abstract

Quasi-2D layers of transition metal dichalcogenides are promising candidates for creating saturable absorbers for pulsed lasers. However, the peculiarities of intense electromagnetic radiation’s influence on such structures have not been thoroughly studied. This paper explores the dynamics of photoexcited carriers in WSe2 flakes through experimental studies. These studies found that WSe2 flakes significantly change their optical properties under the influence of a high-power optical pump, allowed estimating the thermalization time of these structures (about 2 ps), and found that full relaxation takes more than 10 ps. The concentration of carriers in the semiconductor surface layer was estimated to be about 1028 m–3. It was found that standard description models of the optical response based on exciton resonances and absorption by free carriers could not adequately describe the experiments’ results. Thus, for an accurate description of the optical response, it was necessary to consider the effects associated with Coulomb screening that are caused by the high concentration of photo-excited carriers of the optical pumping densities used in this experiment.

Highlights

After their discovery, transition metal dichalcogenides (TMD) became highly promising 2D materials for nanoelectronics devices
The explosive interest in such structures is primarily due to their unique properties, including the presence of a direct nonzero bandgap, real two-dimensionality, chemical and thermal stability, and flexibility. The possibility of these materials’ application in various fields of nano- and optoelectronics, from logic devices [1, 2] and memory cells [3, 4] to biosensors [5] and gas sensors [6], has been demonstrated. Another promising application of these materials is the creation of saturable absorbers working both in the visible [7, 8] and infrared optical ranges [9]
We present our results of photo-induced optical properties’ changes in WSe2 flakes under ultra-short and high-power optical pulses

Summary

Introduction

Transition metal dichalcogenides (TMD) became highly promising 2D materials for nanoelectronics devices. The explosive interest in such structures is primarily due to their unique properties, including the presence of a direct nonzero bandgap, real two-dimensionality, chemical and thermal stability, and flexibility The possibility of these materials’ application in various fields of nano- and optoelectronics, from logic devices [1, 2] and memory cells [3, 4] to biosensors [5] and gas sensors [6], has been demonstrated. The possibility of applying these materials as filters is related to their very high nonlinear optical absorption [10] Such saturable absorbers can be used both in mode-locking and in Q-switching [11,12,13] methods. We present our results of photo-induced optical properties’ changes in WSe2 flakes under ultra-short and high-power optical pulses

Materials and methods

Results and discussion

Conclusions