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Planar laser induced fluorescence (PLIF) imaging can potentially assess ion distributions and coupling in the context of super-Alfvenic ablation plasma expansions into magnetized background plasmas. In this feasibility study, we consider the application of PLIF to rapidly expanding carbon plasmas generated via energetic laser ablation of graphite. By utilizing hydrodynamic and collisional-radiative simulations, we identify schemes accessible to commercially available tunable lasers for the C I atom, the C II ion, and the C V ion. We then estimate the signal-to-noise ratios yielded by the schemes under reasonable experimental configurations.

The values of the laser induced surface damage thresholds for samples of silicon, fused quartz and soda lime glass at both 0.248pm (UV) and 10.6pm (IR) are presented. Experiments are then described where laser damage is induced using crossed UV-IR beams, with varying time delays imposed between the arrivals of the two laser pulses at the sample surface. The results of these crossed beam experiments are then discussed. Order of magnitude reductions in the IR damage thresholds of silicon and glass are observed when the beams are crossed, no such reduction is observed for quartz. Further, only in the case of glass samples is a reduction in the UV damage threshold seen when the beams are crossed. The reduction in IR threshold on silicon has been seen with delays between the laser pulses of up to 100ns. The reduction in IR threshold for glass was seen for delays up to 1.2ms. These results lead to a discussion of the role of so-called seed electrons in the damage process and the mechanisms operative at the different wavelengths.

The construction and performance of a system for the spatial characterization of a CO2 pulsed laser beam is described. Using thermally quenched fluorescence a direct imaging technique has been developed for single shot CO2 laser pulse beam profiling. A CCD video camera and framestore interfaced to a PC computer are used to image the spatial intensity distribution produced by a CO2 pulse incident upon a temperature dependent luminescent screen. The resolution is similar to much more expensive pyroelectric detector array techniques with all the advantages of two dimensional beam processing.

The authors present results which show the topography of the laser-induced periodic surface structures formed upon samples of germanium, which had been irradiated at a wavelength of 248 nm, and fused quartz irradiated at 10.6 mu m. Surface profiles are obtained from phaseshifting interferometry measurements. A slight modification to a theory which models the development of the surface contour during resolidification of a molten surface can be successfully employed to explain their observations upon germanium. To explain the profiles obtained on fused quartz they suggest that plasma oscillations at the surface may be involved.

The values of the laser-induced surface damage thresholds for samples of silicon, fused quartz and soda lime glass at both 0.248 mu m (UV) and 10.6 mu m (IR) are presented. Experiments are then described where laser damage is induced using crossed UV-IR beams, with varying time delays imposed between the arrivals of the two laser pulses at the sample surface. Order of magnitude reductions in the IR damage thresholds of silicon and glass are observed when the beams are crossed, no such reduction is observed for quartz. Further, only in the case of glass samples is a reduction in the UV damage threshold seen when the beams are crossed. The reduction in IR threshold on silicon has been seen with delays between the laser pulses of up to 100 ns. The reduction in IR threshold for glass was seen for delays up to 1.2 ms. These results lead to a discussion of the influence of 'seeding electrons' on the development of laser-induced damage as well as to determine whether the damage mechanisms are similar at each wavelength.

An imaging technique has been developed that, for the first time in a single non-damaging laser pulse, allows enough information about the surface under test to be obtained to enable accurate predictions to be made as to the spatial locations of the first damage sites. The technique is based upon using high resolution schlieren imaging to monitor the deflection of a pulsed probe (dye) laser beam incident on the test surface a few hundred nanoseconds after the surface has been heated by a non-damaging pulse from the main (KrF excimer) laser. It is found for all samples tested (metals semiconductors, dielectrics) that the areas of greatest probe beam deflection are the first ones to damage. Furthermore it is found, in multiple shot experiments, that to a good approximation the order in which areas damage is proportional to the amount of probe beam deflection.

The properties of various glasses used as ultra-violet to visible image converters are investigated. A system is described, based on a glass fluorescer, which writes the beam profile of a single shot KrF laser directly into computer memory and hence permits many powerful image processing routines.

The authors report the results of a study into the formation of periodic damage patterns on nominally smooth Ge surfaces using s-polarised laser light from a KrF excimer laser working at 249 nm. Dependent upon the incident fluence and to a lesser extent the angle of incidence, two types of pattern are found. At low fluences, patterns orientated parallel to the polarisation are found, whilst at higher fluences anomalous patterns that are neither parallel nor perpendicular to the polarisation are observed. By invoking a new formation mechanism for the anomalous patterns, both types of pattern are shown to be consistent with a previously developed theory.

The construction and performance of a system for the spatial characterisation of a CO2 pulsed laser beam is described. A CCD video camera and framestore interfaced to a personal computer are used to image the spatial intensity distribution produced by a CO2 pulse incident upon a temperature-dependent luminescent screen.

The authors present a simple demonstration of the so-called 'breath test' (i.e. the deliberate fogging of a surface with the intention of showing areas of non-uniformity) on laser-irradiated colloidal silica coatings. An explanation of the observed effects is made, based on modifications to the coating structure induced by the laser irradiation.

We report the results of an investigation into the formation mechanism of laser-induced ripple structures based on obtaining direct images of a surface while the transient heating induced by a KrF excimer laser is still present. These images reveal transient but well-defined periodic heating patterns which, if enough subsequent excimer pulses are incident on the surface, become permanently induced ripple structures. It is evident from these transient images that the surface heating is confined to the induced structures, thus strongly supporting the idea that at low fluences the ripples are formed by localizing surface melting.