In-Situ and Ex-Situ Characterization of Femtosecond Laser-Induced Ablation on As2S3 Chalcogenide Glasses and Advanced Grating Structures Fabrication

Abstract

Femtosecond laser pulse of 800 nm wavelength and 150 fs temporal width ablation of As2S3 chalcogenide glasses is investigated by pump-probing technology. At lower laser fluence (8.26 mJ/cm2), the surface temperature dropping to the melting point is fast (about 43 ps), which results in a clean hole on the surface. As the laser fluence increases, it takes a longer time for lattice temperature to cool to the melting point at high fluence (about 200 ps for 18.58 mJ/cm2, about 400 ps for 30.98 mJ/cm2). The longer time of the surface heating temperature induces the melting pool in the center, and accelerates material diffusing and gathering surrounding the crater, resulting in the peripheral rim structure and droplet-like structure around the rim. In addition, the fabricated long periodic As2S3 glasses diffraction gratings can preserve with high diffraction efficiency by laser direct writing technology.

Hierarchical Surface Structures and Large-Area Nanoscale Gratings in As2S3 and As2Se3 Films Irradiated with Femtosecond Laser Pulses

“…It can be seen that the threshold pulse energy, at which the modification of the film surface begins, is 0.36 μJ for As 2 S 3 ( F = 136 mJ/cm 2 ) and 0.05 μJ for As 2 Se 3 ( F = 34 mJ/cm 2 ), respectively. It is worth noting that for As 2 S 3 the fluence exceeds the ablation threshold, which ranges from 7.2 mJ/cm 2 to 24 mJ/cm 2 for femtosecond 800 nm laser pulses according to Refs [ 41 , 42 ]. Presumably, modification of As 2 S 3 requires higher energies of laser pulses because the As–S chemical bonds are stronger than those of As–Se (260 and 230 kJ/mol, respectively) [ 43 ].…”

Effect of Laser Pulse Width and Intensity Distribution on the Crystallographic Characteristics of GeSn Film

“…The heating is over before the electrons can transfer energy to the lattice. Therefore, the interaction of the electrons with the lattice and the heat transfer between the lattices can be ignored during the interaction of the femtosecond laser with the thin film [49]. The time for energy accumulation during fs laser processing is extremely short, and the lattice temperature can be non-equilibrium converted in the order of picoseconds.…”

“…With the shortest pulse width, the sample surface can be heated and cooled rapidly, and more Sn atoms can be incorporated into the Ge lattice. Therefore, thermal diffusion is not significant [49][50][51], and the temperature non-equilibrium transition is fast, which is more favorable for obtaining GeSn crystalline films with a higher Sn component.…”

Fs Laser Patterning of Amorphous As2S3 Thin Films

“…Amorphous As 2 S 3 has a transparency window that ranges between 0.7 µm and 10 µm [25], a bandgap of 2.4 eV [26], and a refractive index of 2.5 [27]. When irradiated with bandgap or intense sub-bandgap light, the surface morphology of As 2 S 3 thin films changes due to photoexpansion [28], photoevaporation/photodepression [29], or ablation [30] processes. Moreover, the presence of gold in gold\amorphous chalcogenide heterostructures can influence the optical and structural properties, but also the volume changes of the material [31].…”