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The spontaneous formation of self-assembled and/or self-organized patterns is a fundamental and technologically significant topic. This process is achieved via a phenomenon called dewetting, should it be thermally induced, or caused by laser exposure. Although dewetting seems to be a well-known phenomenon for metallic and polymeric thin films, no proper investigation regarding glassy thin films seems to have been done. Thus, in the present study we try to elaborate on the process of thermal dewetting applied to glassy thin films of the system Agx(As20S80)100−x.

The effect of the melt stirring rate on the radial distributions of Cu, Sb, and Mg impurities in proustite single crystals grown by the Stockbarger method using accelerated crucible rotation and on the optical quality of the crystals is studied in a broad range of Taylor numbers: from 1.9 × 105 to 7.12 × 107. The radial impurity distributions, measured by electron probe x-ray microanalysis, show random oscillations. The accelerated crucible rotation technique makes it possible to reduce the impurity content of proustite and grow optically superior crystals.

The effect of Si content on the optical quality of proustite single crystals grown by the Stockbarger method using accelerated crucible rotation was studied. The rate of melt stirring was varied in the range corresponding to Taylor numbers from 1.9 × 105 to 7.26 × 107. It was shown that the Si content of the crystals could rise in different stages of the preparation process. Si contents above 5 × 10–3 wt % impaired the optical perfection of proustite crystals, independent of the rate of melt stirring.

We report here refined values of the transformation enthalpy for xanthoconite to proustite (54.81 kJ/mol) and pyrostilpnite to pyrargyrite (40.32 kJ/mol). Additionally, the enthalpy for the transformation of trechmannite to smithite (5.82 kJ/mol) has been determined. The refinement was possible by taking into account a previously unknown dependence of electrochemical signals on the amount of substance undergoing the reduction process.

The electrochemical reduction of xanthoconite, proustite, pyrostilpnite, and pyrargyrite was studied by abrasive stripping voltammetry, a technique which is based upon a preliminary mechanical transfer of trace amounts of the mineral onto the surface of a paraffin impregnated graphite electrode. Because the electrochemical reduction proceeds near to reversibility and is very similar for each pair of minerals, the peak potentials in differential pulse voltammetry can be used to calculate the standard enthalpy of phase transformation of xanthoconite to proustite and of pyrostilpnite to pyrargyrite: ΔT H (xanth → proust) O = 35.46 ± 14.15 kJ/mol and ΔT H (pyrostilp → pyrarg) O = 38.85 ± 6.60 kJ/mol. These values are not accessible otherwise until now.

Pulsed laser damage thresholds have been measured for proustite (Ag3 As S3) as the wavelengths 0.694, 1.065, 1.32 and 10.6 μm. The damage thresholds have been found to vary with both the wavelength and duration of the irradiating pulse. At 1.065 μm damage thresholds are 0.38 J/cm2 for pulses of duration 50 ns a value of 7 MW/cm2 is appropriate. The results suggest that damage is initiated by absorbing inclusions approximately 0.6 μm in diameter embedded within the crystals. These inclusions are heated by an incident pulse to cause catastrophic damage of both the surface and interior of an irradiated sample. A model has been developed to enable a study of the thermal behaviour of inclusions irradiated by laser pulses with Gaussian time-dependence to be made.

The conversion is considered of infra-red radiation into visible in a proustite crystal with the pump and signal waves perpendicular to each other. The angular and spectral parameters as well as the efficiency of such interactions are determined.

The low-frequency unclamped electro-optic coefficients of proustite have been measured at an optical wavelength of 0.6328μm. The results show thatr22 is comparable to that of lithium niobate,r13 andr33 are considerably lower. The maximum theoretical value is calculated at 10.8×10−12 m/V about three times the largest measured coefficient value.

An equation of quadratic form is derived relating the phase mismatchΔk=¦ksum −kpump −kslgnl ¦ in an optical sum-frequency generation process to the angle ψ between the pump and signal wave vectors. For a special value ofkpump a solution ofΔk=0 exists having degenerate roots and consequently a single value of ψ. Because of this it is possible to choose a non-collinear phasematching situation for an optical up-converter which tolerates a much larger signal beam divergence than if a collinear-beam interaction were chosen. The case of up-conversion of 10.6μm radiation to the visible, using ruby-laser pumped proustite was chosen as an example for experimental study. Under tangential phase-matching conditions an angular acceptance angle of the infra-red beam of 300 mrad was achieved for a crystal 0.45 cm long.

There is at present great interest in crystals which are suitable for efficient mixing at optical frequencies. Such a crystal should be acentric, have a wide transmission band, have a large non-linear coefficient and permit phase matching. Proustite possesses such properties [1], and this paper summarises the information that has been obtained to date at R R E on these properties and their use in “up-converting” 10μm radiation to the visible, on the available optical quality, on the electro-optic effect, and on electrical conduction in the crystal; some general observations on the type of damage caused to proustite by laser beams are given.

THE compounds silver orthothioarsenite, Ag3AsS3, and silver orthothioantimonite, Ag3SbS3, occur in nature as small imperfect crystals and have been given the mineral names proustite and pyrargyrite, respectively. Harker1 determined their structures and assigned them to the space group R3c. They are non-centrosymmetric uniaxial crystals with a large refractive index, large negative birefringence (n0–ne>0.2) and transmission over a wide spectral range (0.6–13 µm). They also exhibit semiconducting, photoconducting and piezoelectric properties.