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Results of a study of laser induced damage of ion beam sputtered single layers and capped single layers of Sc2O3, HfO2 and Ta2O5 in a controlled atmosphere and in an ultra-high vacuum (UHV) show the choice of material is paramount to achieving the best performance.

We demonstrate that transparent magnesium aluminate spinel ceramic possesses excellent thermo-optical properties, a record low absorption loss of 6 ppm/cm, and superior ruggedness which position it as a prime candidate for an exit window aperture for high energy laser systems, especially in hostile environments. We also demonstrate lasing with an efficiency of about 45% in transparent Yb3+:Y2O3 ceramic made by hot pressing high purity submicron co-precipitated powder. This paves the way forward for high power solid state lasers exploiting hosts with higher thermal conductivity than YAG.

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.

We show that the concentration of oxygen defects trapped in Sc2O3 films by ion beam sputtering can be controlled by modifying deposition conditions. These defects play a role in the optical and structural properties of the thin film metal-oxides.

We have investigated the ion beam sputtering (IBS) of Y2O3 as an alternative to HfO2 for high index layers in interference coatings for high power lasers. We present results on structural and optical properties of Y2O3 deposited from an oxide target. The IBS Y2O3 films are amorphous with a surface roughness of

We have investigated the role of native point defects in the laser damage behavior of amorphous thin films of Sc 2 O 3 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 Sc 2 O 3 . This effect, as shown by the model and confirmed by experiments, is pulse duration dependent.

Small variations of oxygen partial pressure during the ion beam sputtering of metal oxides strongly influence the optical properties, causing an increase in the absorption loss and a decrease in laser damage fluence.

Scandium oxide is an attractive candidate for the engineering of interference coatings, although not widely explored. This paper describes the ion beam sputtering of Sc 2 O 3 . It is shown that the structural properties of the material are affected by the deposition conditions. Laser damage in different regimes of pulsewidths is investigated. These results show that the 1-on-1 laser damage fluence, in both the thermal and deterministic regimes, varies with deposition conditions but this is not the case for S-on-1, indicating that laser-induced defects are important.

Scandium oxide films were deposited using reactive dual ion beam puttering. At 1 micron, the refractive index of the films is 1.95 and the absorption loss is 18.5 ppm. X-ray photoelectron spectroscopy showed oxygen defects.

We discuss the physical and optical properties of Sc 2 0 3 single layers deposited by the dual ion beam sputtering technique at oxygen partial pressures ranging from 1.7 x 10 -5 to 5.1 × 10- 5 Torr. The films are amorphous with crystallite size ~10 nm and have surface roughness RMS values of 1.2 ± 0.3 nm. The refractive index at 1 μm is 1.95. Absorption loss is shown to be sensitive to the oxygen partial pressure during growth. Multiple-pulse damage experiments suggest that the scandia film deposited at the higher oxygen partial pressure accumulates laser-induced trap defects more slowly than the scandia film deposited in a lower oxygen partial pressure atmosphere.

Post-annealing of HfO2and SiO2thin films affects the absorption loss at 1 ?m, and the subpicosecond laser breakdown. These effects are explained by modifications in the density of intrinsic defects and photo-induced defects respectively.

We present a complete systematic study on the effect of assist beam energy on SiO 2 /HfO 2 quarter wave stacks deposited by dual ion beam sputter (DIBS) deposition. Increasing assist beam energy results in lower surface roughness and reduced micro-crystallinity. The coatings also show reduced mechanical stress. The improvements in the structural properties are accompanied by a reduction in the absorption loss and an increase in the laser resistance to damage at 1 μm.

In this work we use electron spin resonance (ESR) spectroscopy to investigate defects in dual ion beam sputtered HfO 2 and SiO 2 films. "As-grown" SiO 2 films exhibit an ESR feature consistent with an E' center associated with an oxygen vacancy previously reported. A similar feature with axial symmetry is seen in HfO 2 films. The defect giving rise to the HfO 2 ESR feature is distributed throughout the film. In addition, post process annealing of HfO 2 and SiO 2 films greatly reduces these defects.

Loss, stress and surface roughness in ion-beam deposition of HfO2/SiO2interference coatings are assessed for different growth conditions to understand how to improve the performance of these coatings for high power laser applications.

We investigate the variations that occur with changes in the number of layers and with the use of the assist beam main and assist beam energy on the morphology of HfO 2 /SiO 2 quarter wave stacks deposited by dual ion beam sputtering. We show how the addition of sequential HfO 2 /SiO 2 bilayers, up to eight, affects the surface roughness and micro-crystallinity of the top HfO 2 layer. We also show that use of the assist source significantly smooths the surface while simultaneously reducing microcrystallinity. The HfO 2 /SiO 2 structures are very robust and can withstand fluences in excess of 3 J/cm 2 generated by 1ps pulses from a chirped amplified Ti:Sapphire laser.

The influence of process conditions on loss, refractive index, and laser induced damage threshold of HfO2/SiO2thin films grown by ion beam assisted sputtering is investigated to realize films with losses less than 20 ppm.

HfO 2 /SiO 2 and ZrO 2 /SiO 2 high reflectors at 1.064 microns were deposited by pulsed reactive DC magnetron sputtering. These dielectric thin film high reflectors were deposited with and without the use of an electron source. The electron source greatly decreased arcing of the magnetrons during the deposition process resulting in thin films with fewer defects. The high reflectors were laser damage tested at 1.064 microns. The optical properties of the thin film coatings were characterized prior to laser damage testing. Optical characterization techniques included angle resolved scatter (BRDF), total integrated scatter (TIS), and adiabatic calorimetry. The dependence of the laser damage threshold and optical properties on deposition conditions is reported.

Optical fields propagation through the Earth's turbulent atmosphere are subject to time varying phase distortions. These phase distortions place severe limitations on electro- optical systems, such as imaging, tracking and vibrometry sensors. The generation of artificial beacons by laser backscatter (guide stars) for wavefront sensing may not be acceptable and natural beacons for wavefront sensing may not be available. Diversity techniques, however, allow passive wavefront measurement of the aberrated wavefront. This paper reports a phase diversity method based upon the transport- of-intensity equation for recovering phase from irradiance measurements. Digitized intensity data over a rectangular array of data is expanded into Zernike polynomials and a matrix method used to solve the transport-of-intensity equation. The phase diversity technique is evaluated in the pupil as well as the focal plane. Simulation and experimental data is provided.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.