Yejia Xu

Point defects in Sc 2 O 3 thin films by ion beam sputtering

We show that the concentration of oxygen interstitials trapped in Sc2O3 films by ion beam sputtering from metal targets can be controlled by modifying deposition conditions. We have identified point defects in the form of oxygen interstitials that are present in Sc2O3 films, in significantly high concentrations, i.e., ∼10(18)  cm(-3). These results show a correlation between the increase of oxygen interstitials and the increase in stress and optical absorption in the films. Sc2O3 films with the lowest stress and optical absorption loss at 1 μm wavelength were obtained when using a low oxygen partial pressure and low beam voltage.

Spatio-TEmporally REsolved Optical Laser Induced Damage (STEREO LID) technique for material characterization

A technique for measuring the ablation and laser-induced damage threshold (LIDT) by identifying the temporal onset of damage and location of initiation within the beam profile is demonstrated. This new method, dubbed Spatio-TEmporally REsolved Optical Laser Induced Damage (STEREO LID), is compared to traditional damage tests and its advantages are exemplified.

Determination of defect densities from spatiotemporally resolved optical-laser induced damage measurements.

A procedure is developed to retrieve defect densities of optical coatings and surfaces from spatiotemporally resolved optical-laser induced damage (STEREO-LID) measurements. In STEREO-LID, the temporal onset and location of nanosecond laser damage initiation is measured for each excitation event. The power of STEREO-LID relative to traditional damage tests resulting in damage probabilities is characterized with LID data from Monte Carlo simulations.

What role do defects play in the laser damage behavior of metal oxides

We have investigated the role of native point defects in the laser damage behavior of amorphous thin films of Sc2O3 deposited by ion beam sputtering. Through systematic characterization and detailed modeling we show that native defects influence the 1-on-1 laser induced damage threshold fluence of the Sc2O3. This effect, as shown by the model and confirmed by experiments, is pulse duration dependent.

Comparison of defects responsible for nanosecond laser-induced damage and ablation in common high index optical coatings

Abstract. 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.

Femtosecond to nanosecond laser damage in dielectric materials

We present a consistent model supported by experimental data of damage of dielectric films by femtosecond to nanosecond pulses. Special emphasis is given to the role of defects and transient processes in the material. New imaging and diagnostic techniques are discussed to characterize the film performance.

New developments in optical coating characterization and utilization under high power laser irradiation

We present a novel technique to characterize coating imperfections that limit the performance under pulsed laser irradiation. We also discuss the use of 1D photonic crystals based on dielectric metal oxides as nonlinear optical frequency converters.

Comparative STEREO-LID (Spatio-TEmporally REsolved Optical Laser-Induced Damage) studies of critical defect distributions in IBS, ALD, and electron-beam coated dielectric films

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.