Rudolf August Herbert Heinecke

1.064-μm laser damage studies of silicon oxy-nitride narrow band reflectors

In a paper presented at the 1992 Boulder Damage Symposium, we discussed the role of electric field effects, defect type, surface roughness, film thickness and coating absorption on the laser damage thresholds of sinusoidally modulated, plasma deposited, silicon oxy-nitride narrow band reflectors. We concluded that the damage threshold, which was essentially constant at 2 J/cm2 at the test wavelength of 0.532 micrometers , was defect dominated. A sizeable fraction of the damage events occurred at a particular type of defect--a hemispherical hillock feature typically 5 micrometers in diameter as identified by SEM and interferometric surface profiling. We postulated that this defect initiated damage because of either a microlensing effect or an enhanced electric field effect. We have since measured the laser damage thresholds of all these samples at 1.064 micrometers , and found significant variations in the damage thresholds, which were a factor of three higher on average than those at 0.532 micrometers . The microlens model presented can explain damage thresholds up to a factor of four higher at the longer wavelength, and predicts a minimum nodule height for increased damage susceptibility. The minimum nodule height is dependent on the wavelength and the coating average index. The wavelength scaling of the fluence enhancement and the minimum nodule height imply that nodule initiated damage will become an even more serious problem as the wavelength approaches the UV.

TfI8: Pulsed plasma deposition of lead lanthanum zirconate titanate(PLZT) and lead lanthanum titanate(PLT)

Abstract Thin films of ferroelectric lanthanum-modified lead zirconate titanate (PLZT) and lanthanum-modified lead titanate (PLT) have been prepared using a novel high-powered pulsed plasma deposition technique. This method uses a microwave-induced intense discharge in a low pressure gas containing organometallic precursors of each of the required metal atoms, together with carbon dioxide and argon. In the discharge, the precursors dissociate to produce atoms which then recombine on the substrate to form the oxide film. Results are presented on the composition and crystal form of the films as the deposition conditions are varied. By careful control of deposition temperature, it is shown that a microcrystalline perovskite phase may be grown on a wide variety of substrate materials.

Plasma etching and deposition as a method of polishing CVD diamond

As grown, CVD diamond windows have low infra-red absorption, but are highly scattering in transmission due to the presence of crystalline facets on the material surface. Conventionally, these facets are removed by mechanical polishing techniques which are slow, not easily adapted to complex shapes, and which can lead to mechanical damage and loss of strength. In this work, an attempt has been made to use a patented plasma etching and deposition method to polish CVD diamond window material optically flat. Low pressure radio frequency (rf) discharges of a variety of plasma etchant gases (Ar, H2 CCl4, SF6, CO2) have been used to etch the diamond surface. Etch rates of 2000 angstroms/minute can be obtained using carefully optimized etch chemistries. It has been shown that plasma etching the diamond window under conditions which give a high self-induced dc bias causes preferential sputtering of the edges of microcrystallites and hence polishes the diamond surface flat. Certain plasma chemistries, notably those involving chlorine, have also been found to flatten the surface by preferentially removing the crystalline facets. By plasma depositing silicon oxide on the window material it is possible to planarize the surface prior to a plasma etch stage and then plasma etch away the silicon oxide and diamond in a subsequent etch stage so smoothing the diamond surface. The affect of these polishing methods on a variety of CVD diamond films is discussed and the limitations of the technique addressed.

Laser damage studies of silicon oxy-nitride narrowband reflectors

A series of sinusoidally modulated, plasma deposited, silicon oxy-nitride, narrow band reflectors have been examined with a view to understanding the relative roles of electric field effects, defect type, surface roughness, thickness, and coating absorption on the laser damage threshold. The damage threshold measurements were made at 0.532 micrometers with a range of spot sizes, a pulse length of 15 ns (full width at half maximum intensity), and each site was tested with 100 shots at a 10 Hz repetition rate. The damage threshold was essentially constant at around 2 J/cm2 for all the samples, and was defect dominated. Three types of topological defects were discovered using a WYKO three dimensional surface profiler, and one of the defect types was responsible for a large fraction of the damage events. It is postulated that this 5 micrometers hemispherical defect may behave either as a microlens which enhances the peak fluence that the underlying coating is subjected to, or as a center for enhanced electric field effects.