Ultrafast damage dynamics and ablation mechanism of GaSe induced by femtosecond laser irradiation

Abstract

With the development of high-power infrared lasers and optical devices based on GaSe, more attention has been paid to its optical damage under laser irradiation. Understanding the interactions at the surface of GaSe during femtosecond laser irradiation is essential for its applications as infrared nonlinear optical and optoelectronic devices. Here, ultrafast damage dynamic process and ablation mechanism of GaSe under femtosecond laser irradiation are studied. Two types of damage/ablation mechanisms are proposed according to two distinct types of damaged morphologies and damaged products, and further confirmed by ultrafast pump–probe spectroscopy. At lower fluences, the laser-induced damage of GaSe can be attributed to the formation of new products by chemical bonds broken and phase transitions, changing the stoichiometry and spectra while barely destroy surface morphologies. At higher fluences, surface plasma is formed with massive hot free electrons in the conduction band from the multi-photon ionization and avalanche ionization. The plasma heats the surface and forms shock wave, which removes the surface layer by vaporization, causing a damage pit on the surface. Our results gain insight into damage dynamics of GaSe under laser irradiation, which can help to have a deeper comprehension of the laser-materials interaction.