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Spatio-TEmporally REsolved Optical Laser-Induced Damage, or STEREO-LID, is a novel laser damage technique which measures the actual fluence (and intensity) at which damage occurs in a single pulse. This is accomplished by measuring the initiation time during the pulse and the initiation position within the beam profile. This technique has been demonstrated in the measurement of the defect distribution of single films and surfaces. In this paper, we demonstrate the technique to characterize laser-induced damage in high reflectors by single 8.3 ns pulses at 1064 nm. The high reflectors were quarter-wave stack of HfO2/SiO2 on a fused silica substrate. Applying STEREO-LID to high reflectors required a change in geometry as the technique previously used light transmitted through the optic. Instead, the initiation time is identified by a disruption of reflection and scattered light. The initiation position is determined by imaging the backscattered laser light. The STEREO-LID results are compared to the traditional 1-on-1 damage test to show that it is superior at detecting critical fluence limiting defects.

Lawrence Livermore National Laboratory (LLNL) and Colorado State University (CSU) have co-developed a planarization process to smooth nodular defects. This process consists of individually depositing then etching tens of nanometers of SiO2 with a ratio of 2:1, respectively. Previous work shows incorporating the angular dependent ion surface etching and unidirectional deposition reduces substrate defect cross-sectional area by 90%. This work investigates the micro-structural and optical modifications of planarized SiO2 films deposited by ion beam sputtering (IBS). It is shown the planarized SiO2 thin films have ~3x increase in absorption and ~18% reduction in thin film stress as compared to control (as deposited) SiO2. Planarized SiO2 films exhibit ~13% increase in RMS surface roughness with respect to the control and super polished fused silica substrates. Laser-induced damage threshold (LIDT) results indicate the planarization process has no effect on the onset fluence but alters the shape of the probability vs fluence trace.

High reflection Ta2O5/SiO2 and HfO2/SiO2 interference coatings that incorporate top thick layers of SiO2 with superior performance are demonstrated for 1-2μm high energy lasers are demonstrated.

The laser damage behavior of high quality coatings under nanosecond pulse illumination is controlled by statistically distributed defects, whose physical nature and defect mechanisms are still largely unknown. Defect densities are often retrieved by modeling the fluence dependence of the damage probability measured by traditional damage test (TDT) methods, based on ‘damage’ or ‘no damage’ observations. STEREO-LID (Spatio-TEmporally REsolved Optical LaserInduced Damage) allows the determination of the damage fluence (and intensity) in a single test by identifying the initiation of damage both temporally and spatially. The advantages of this test method over the TDT are discussed. In particular, its ability to retrieve detailed defect distribution functions is demonstrated by comparison of results from HfO2 films prepared by ion-assisted electron beam evaporation, ion-beam sputtering, and atomic layer deposition.

Spatiotemporally resolved optical laser-induced damage is an experimental technique used to study nanosecond laser damage and initiation of ablation in dielectric metal-oxide films used for optical coatings. It measures the fluence (intensity) at the initiation of damage during a single laser pulse. The technique was applied to coatings of HfO2, Sc2O3, and Ta2O5, which were prepared by ion-beam sputtering, and HfO2 which was prepared by electron-beam evaporation. Using the data obtained, we were able to retrieve the defect density distributions of these films without a priori assumptions about their functional form.