Investigation of Second- and Third-Harmonic Generation in Few-Layer Gallium Selenide by Multiphoton Microscopy

TLDR

Gallium selenide is a layered semiconductor and a well‑known nonlinear optical crystal, and the discovery of graphene has spurred extensive research into two‑dimensional materials. The study reports on the nonlinear optical properties of few‑layer GaSe using multiphoton microscopy. Multiphoton microscopy was employed to probe the second‑ and third‑harmonic generation of few‑layer GaSe flakes. Both second‑ and third‑harmonic generation were observed, and unexpectedly a peak at 390 nm—attributable to fourth‑harmonic or sum‑frequency generation—was detected in thin GaSe flakes.

Abstract

Abstract Gallium selenide (GaSe) is a layered semiconductor and a well-known nonlinear optical crystal. The discovery of graphene has created a new vast research field focusing on two-dimensional materials. We report on the nonlinear optical properties of few-layer GaSe using multiphoton microscopy. Both second- and third-harmonic generation from few-layer GaSe flakes were observed. Unexpectedly, even the peak at the wavelength of 390 nm, corresponding to the fourth-harmonic generation or the sum frequency generation from third-harmonic generation and pump light, was detected during the spectral measurements in thin GaSe flakes.