A great deal of interest has been shown in the potential of rugate designs for the realization of dielectric mirrors with enhanced resistance to laser induced damage. Some of the benefits are arguably a result of the fact that the mirrors are essentially composed of inhomogeneous materials, with the effective refractive index continuously varying between the two limits defined by the particular design selected. A study has been carried out of the potential of three different processes for the fabrication of mirrors using a 40 period silicon oxynitride mirror design for 532nm, with design goals of R equals 99.9 percent and bandwidth close to 10 percent. The study has compared reactive magnetron sputtering, ion assisted deposition and microwave plasma CVD. Conventional quarter wave stacks were also produced for use at the same wavelength, with the same number of periods to act as a reference. Laser damage thresholds were measured using a Q-switched YAG laser at both the resonance band of the stack and off-resonance at 1064nm. The results highlight the role of mirror design, process characteristics and film morphology.

It has been shown that an all solid-state porous silicon electroluminescent device with an efficiency greater than 0.1% can be fabricated (A. Loni et al., Electron. Lett., 31 (15) (1995) 1288–1289). However, one important factor limiting the practical application of this device is the stability of the electroluminescence. With the support of optical, electrical and chemographical investigations, we report on the factors which might affect the stability of the device, such as operating environment, choice of contact materials, localised electrical breakdown, contact diffusion and the surface passivation of the porous silicon. For devices fabricated with semi-transparent gold contacts, it is shown that the gold is permeable to air and device degradation correlates with oxidation of the porous silicon when operated in air. Devices fabricated with less permeable indium tin oxide contacts are shown to be significantly more stable in air. The degradation of devices with indium tin oxide contacts does not correlate with oxidation, diffusion of contact material or localised electrical breakdown. However, the degradation is accompanied by the loss of surface hydride passivation from the porous silicon.

There has been a growing interest in new laser systems for use at mid-IR wavelengths, driven by requirements for a number of diverse applications. Developments in mid-IR coating technology are following three major thrusts. In the first, the potential of ion-assisted process is being exploited and the technology is already becoming well established in the optical coating industry. In the second, the benefits of using gas-phase precursors are being explored, driven by the potential of avoiding the generation of second phase inclusion in the coatings with associated reduction in laser damage threshold.Research is also addressing the use of nanocomposite materials with an engineered microstructure to produce coatings with dielectric properties of choice. This paper presents a review of progress in some of these areas with special emphasis on the comparison of the properties of materials at DF laser wavelengths. Evidence is presented which suggests that laser damage thresholds at 3.8 micrometers are determined by residual hydroxyl-related absorption in the films. Ion- assisted processes do not necessarily provide the best way forward for the highest damage thresholds.