Laser damage study of nodules in electron-beam-evaporated HfO_2/SiO_2 high reflectors

Abstract

A reactive electron beam evaporation process was used to fabricate 1.064 μm HfO2/SiO2 high reflectors. The deposition process was optimized to reduce the nodular density. Cross-sectioning of nodular defects by a focused ion-beam milling instrument showed that the nodule seeds were the residual particles on the substrate and the particulates from the silica source "splitting." After optimizing the substrate preparation procedure and the evaporation process, a low nodular density of 2.7/mm2 was achieved. The laser damage test revealed that the ejection fluences and damage growth behaviors of nodules created from deep or shallow seeds were totally different. A mechanism based on directional plasma scald was proposed to interpret observed damage growth phenomenon.

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

“…The details of our modified EBE process using oxygen radicals were given in a previous study. 22 HfO 2 /SiO 2 HR coatings with a wavelength of 1.064 mm and normal incidence angle were used in this study. The design was [air: L(LH)ˆ1 3 glass], where H is a quarter-wave HfO 2 layer, and L is a Nanosecond laser damage of nodular defects in multilayers XB Cheng et al 2 quarter-wave SiO 2 layer.…”

“…The raster scan was halted when either more than 100 nodules were ejected or catastrophic damage occurred. The laser energy originated from a specific fluence that was based on previous experience and that was gradually increased to the 'stop' fluence using increments of 5 J cm 22 . The maximum output power on the sample surface was 170 J cm 22 .…”

“…The laser energy originated from a specific fluence that was based on previous experience and that was gradually increased to the 'stop' fluence using increments of 5 J cm 22 . The maximum output power on the sample surface was 170 J cm 22 . Following the damage test, the damage morphologies of the ejected nodules were identified first under a Nomarski microscope and were then characterized using focused ion beam (FIB) technology.…”

Theoretical study of laser induced thermal damage on the narrowband filter optical thin film

“…The laser induced damage is a crucial factor in the application of optical thin film, which is related to the robustness of the whole laser system. The damage mechanisms of optical thin film have been extensively studied by researchers in theory and experiment [2][3][4][5][6] . There are two types of mechanisms in the damage of optical thin film: thermal effect and field effect, which are responsible for the high energy laser induced damage and the high power laser induced damage, respectively [2] .…”

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

“…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.)…”