Nanosecond laser pulse induced concentric surface structures on SiO_2 layer

Abstract

Abstract:We report the periodic concentric surface structures on SiO 2 layer induced by a single shot nanosecond laser pulse at 1.06 μm. The fringe period of the structures ranges from 7.0 μm to 26.8 μm, depending on the laser fluence and the distance from central defect precursor. The size and depth of the damage sites increase almost linearly with the laser fluence from 19.6 J/cm 2 to 61 J/cm 2 . Plasma flash was clearly observed during the damage process. We attribute the formation mechanism of the structures to the interference between the reflected laser radiations at the air/shock-front and the shock-front/film interfaces.

Comparison of the damage features of the silica films prepared by the sol-gel and e-beam deposition methods

“…The laser-induced concentric surface structures are observed on the surface of both the EBD and sol-gel silica single layer in the OM images. The concentric morphologies in EDB SiO 2 films have been reported in our previous work [12]. Now we find the similar morphologies in SiO 2 sol-gel coatings.…”

“…Figure 8 The SEM morphology of the damage pit on the sol-gel silica coating is shown in Figure 9. Unlike the explosive boiling phenomenon [12] on the surface of the EBD silica coating, the observed concentric rings are related with the mechanical interaction. The top part in the figure is a complete damage morphology.…”

“…Silica coating is widely used as an antireflective optical component in the high power laser systems owning to its high laser-induced damage threshold (LIDT) and excellent optical and thermomechanical properties [8][9][10].Various surface morphologies, such as periodic ripples, concentric rings [11,12], porous nanoparticles and microbumps [13], were found to be related with the different energy coupling mechanisms that dependent on the specific nature and structure of the material during the femtosecond or nanosecond laser ablation. Concentric rings of the porous silica coating induced by the nanosecond laser were observed in the previous publications [14,15], which were similar to those on the surface of the coatings deposited by the physical vapor deposition method [11,12,16]. Electron beam deposition and sol-gel are two general methods to prepare silica films [8].…”

Origin of the plasma scalds in dielectric coatings induced by 1ω laser

“…4 The occurrence of plasma scalds has been widely recognized as the typical damage morphology of 1x pulse in air and has continued to attract many researchers in recent years. [8][9][10][11][12] However, the fundamental physical mechanism by which laser-coating interaction leads to the plasma scalds on the capping layer is still obscure. The aim of this work is to reveal the origin of the plasma scalds in dielectric coatings induced by a 1x laser.…”

Beam modulation caused by the plasma scalds in the multilayer dielectric films

“…Knowledge of the beam modulation caused by the plasma scalds is particularly important in estimating the tolerant dimension of the plasma scalds during the laser conditioning and arrangement of the downstream optical components. Based on the previous characterization about the plasma scalds [18,19], a mixed overcoat layer model is newly proposed to analyze the near-field phase modulation (NFPM) in this Letter. With the NFPM, we calculate and discuss the far-field intensity modulation (FFIM) using the scalar diffraction theory [20].…”