Femtosecond laser irradiation on Nd:YAG crystal: Surface ablation and high-spatial-frequency nanograting

Abstract

In this work, we systematically study the surface modifications of femtosecond (fs) laser irradiated Nd: YAG crystal in stationary focusing case (i.e., the beam focused on the target in the steady focusing geometry) or dynamic scanning case (i.e., focused fs-laser beam scanning over the target material). Micro-sized structures (e.g. micro-craters or lines) are experimentally produced in a large scale of parameters in terms of pulse energy as well as (effective) pulse number. Surface ablation of Nd:YAG surface under both processing cases are investigated, involving the morphological evolution, parameter dependence, the ablation threshold fluences and the incubation factors. Meanwhile, under specific irradiation conditions, periodic surface structures with high-spatial-frequency (<k/2) can be generated. The obtained period is as short as 157 nm in this work. Investigations on the evolution of nanograting formation and fluence dependence of period are performed. The experimental results obtained under different cases and the comparison between them reveal that incubation effect plays an important role not only in the ablation of Nd:YAG surface but also in the processes of nanograting formation.

Tuning the period of femtosecond laser induced surface structures in steel: From angled incidence to quill writing

“…When a material surface is exposed to laser light under certain conditions in terms of pulse number, pulse duration, fluence, and light polarization, it is possible to fabricate self-organized surface structures, known as Laser Induced Periodic Surface Structures (LIPSS) [7]. LIPSS can be fabricated in metals [8][9][10][11][12], semiconductors [13][14][15], dielectrics [16][17][18][19], which has generated an enormous interest in the scientific community due in order to unravel the underlying mechanisms, as well as in industry because of the countless applications that are foreseen for these structures. Amongst the variety of different structure types that can be fabricated, the most common ones are the so-called ripples (parallel lines with a period near the laser wavelength usually perpendicular to its polarization), grooves (parallel lines with supra-wavelength period orientated parallel to the polarization), and spikes (disordered supra-wavelength cone-like structures).…”

Plastic deformation as nature of femtosecond laser writing in YAG crystal

“…Stripes were perpendicular to the track, but again parallel to [100]. The regular structure has a common nature neither with the laser induced periodic surface structure (LIPSS) observed in YAG 50 , nor with volume nano-gratings observed in fused silica 12 . These statements are supported by experimental facts: (1) orientation of the stripes follows crystallographic axes and is not related to polarization; (2) the structure is not formed under high overlap of laser pulses.…”

Femtosecond laser-inscribed optical waveguides in dielectric crystals: a concise review and recent advances

“…61,62 As a result, the femtosecond laser modification of the dielectrics is very localized, which enables "cold" micromachining of materials. The femtosecond laser modification may bring out some effects in dielectrics, such as refractive index changes, 33 stress, 63 birefringence, 64 nanogratings, 65,66 voids, 67,68 and thermal melting. 69 To promote permanent refractive index changes in the focal volumes, which are the base for waveguides, the pulse intensity has to be carefully controlled to avoid breakdown.…”