The effect of an electric field on the thermomechanical damage of nodular defects in dielectric multilayer coatings irradiated by nanosecond laser pulses

Abstract

Thermomechanical damage of nodules in dielectric multilayer coatings that are irradiated by nanosecond laser pulses has been interpreted with respect to mechanical properties and electric-field enhancement. However, the effect of electric-field enhancement in nodular damage, especially the influence of electric-field distributions, has never been directly demonstrated through experimental results, which prevents the achievement of a clear understanding of the damage process of nodular defects. Here, a systematic and comparative study was designed to reveal how electric-field distributions affect the damage behavior of nodules. To obtain reliable results, two series of artificial nodules with different geometries and film absorption characteristics were prepared from monodisperse silica microspheres. After establishing simplified geometrical models of the nodules, the electric-field enhancement was simulated using a three-dimensional finite-difference time-domain code. Then, the damage morphologies of the artificial nodules were directly compared with the simulated electric-field intensity profiles. For both series of nodules, the damage morphologies reproduced our simulated electric-field intensity distributions very well. These results indicated that the electric-field distribution was actually a bridge that connected the nodular mechanical properties to the final thermomechanical damage. Understanding of the damage mechanism of nodules was deepened by obtaining data on the influence of electric-field distributions on the damage behavior of nodules.

Laser-induced damage of intrinsic and extrinsic defects by picosecond pulses on multilayer dielectric coatings for petawatt-class lasers

“…PE defects change slightly but remain stable up to 50 to 100 shots at fluences at or below 5 J∕cm 2 ; similar changes were observed during raster scanning (with 1 to 2 higher fluence shots), see Fig. 5(b) for Type I damage (most probably similar to a gentle nodular ejection, as observed for the case of subgrowth threshold, ns-pulse damage of artificial nodular defects 29,30 ). ii.…”

Nanosecond laser-induced damage of nodular defects in dielectric multilayer mirrors [Invited]

“…Our previous works investigated the effect of the electric field on the thermomechanical damage of artificial nodules in the HR coatings irradiated by a 1064 nm nanosecond pulsed laser [7,8]. To obtain reliable laser damage testing results, two series of artificial nodules with different geometries and film absorption characteristics were prepared from monodisperse SiO 2 microspheres.…”

Comprehensive studies of IR to UV light intensification by nodular defects in HfO2/SiO2multilayer mirrors

“…6,9,23 Within this study two parameters nodular defects have been chosen for detailed examination under applied laser radiation. Firstly, light intensification is known to increase with inclusion diameter.…”

“…Multiple studies have been performed on properties of the nodular defects, 2, 7-14 their growth mechanism 8,[15][16][17][18][19] and interaction with applied laser radiation. 5,6,12,[20][21][22][23] Light intensification by nodules has been shown to be sensitive to various defect characteristics (such as size, geometry, depth, etc.) as well as laser irradiation conditions (wavelength, polarization, angle of incidence, etc.)…”

“…as well as laser irradiation conditions (wavelength, polarization, angle of incidence, etc.) 5,6,12,[20][21][22][23] Up to now most of the parametric studies were carried out for the infrared (IR) spectral range. There is still a lack of knowledge on wavelength dependence of light intensification.…”