http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:21978 Microspheres made from optical glasses such as silica and chalcogenide are used as both passive and active optical elements in micro-optics systems and devices. The homogeneity of the microspheres is crucial to their optical quality and performance in such devices and so it is essential, in optimizing such systems, that techniques with nanometer scale resolution are developed to measure the internal structure and homogeneity of such spheres. In this work an analytical protocol based on focussed ion beam milling, combined with secondary ion and secondary electron imaging, has been developed to study the internal homogeneity of glass microspheres. The results have shown that silica microspheres with diameters of three to five microns, fabricated by a sol-gel method, have internal inhomogeneities and voids that will lead to non-uniform optical properties. The FIB milling and imaging technique developed has been found to be a very useful method of studying such inhomogeneities, which have been proposed, but never previously observed, in glass microspheres. The FIB based technique has also been used on larger chalcogenide glass (Ga₂S₃:La₂S₃) microspheres (diameter of order 70 microns) but no inhomogeneities have been observed at the spatial resolution of a few microns so far achieved for these larger microspheres. This study suggests that the FIB based milling and imaging technique may have potential for quantitative use in the measurement of morphological variations in such systems as well as in the study of aging processes in micron-sized glass spheres. 2012-10-10T05:51:28.986Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20160 Certain spider webs are composed of several types of micro-optical elements made from transparent optical materials. The silks (radial and capture) are almost exclusively protein. The nearly cylindrical silks have diameters in the range 0.1 to several microns and cross-sectional morphology that is cylindrical-multi-layered,.as studied by transmission electron microscopy, The capture threads are coated with aqueous adhesive that also forms into nearly elliptical micro-lenses (adhesive droplets) mounted on the near cylindrical silks. The remaining elements of the web are the cement junctions tying the radial and the capture threads of the web together. These are irregularly shaped platelets. Progress to date on our research characterizing the optical properties and function of these transparent orb webs has been to interpret the reflection and transmission properties of the elements of the web, and the web as a whole, in natural lighting; to evaluate the optical finish of the surface of the silks and capture droplets; and to measure the principal refractive indices of radial silks using new immersion based methods developed for application to micron-sized, curved optical elements. Here we report the principal refractive indices, birefringence, dispersion and morphology of transparent spider silk subject to various chemical treatments. The morphology is measured using TEM. Insight into the physical origin of the refractive index properties will be discussed. 2012-08-29T02:10:11.849Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20157 In previous research we introduced an experimental methodology in which focused-ion-beam (FIB) sectioning, followed by secondary ion (SI) and secondary electron (SE) imaging, was used for testing the internal material homogeneity of silica and chalcogenide glass microspheres. The methodology is readily applied to micro-optics with dimensions of a few microns. The use of both SI and SE imaging of the sequentially sectioned samples was shown to allow accurate assignment of inhomogeneities, voids and other imperfections as being within the footprint of the micro-optic. On larger micro-optics FIB sectioning can become prohibitively time intensive and can require the use of too much platinum in sample preparation for evaluation of the bulk of the micro-optic. However, improved sample preparation and image analysis has enabled high magnification and high sensitivity study of the glass near the surface of chalcogenide microspheres with diameter of order 70μm. The chalcogenide glass is Ga₂S₃/La₂S₃, in a 70/30 weight percent ternary (GLS) and the microspheres had been kept in air, in normal laboratory conditions, for about two years prior to testing. Evidence of an altered layer with a width of the order of 0.1μm near the surface and then an outer porous layer at the surface was found. Lower resolution studies are then reappraised in light of the high resolution measurements. 2012-08-29T01:56:17.388Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20863 Glasses used in photonics research and industry are required to be homogeneous and stable. Our study of chalcogenide microspheres indicates that significant deterioration can take place at the surface of such micro-optics in a few years at normal environmental conditions. Chalcogenide glass (Ga₂S₃:La₂S₃, 70:30 (GLS)) microspheres of order one hundred microns in diameter have been focused ion beam (FIB) milled and imaged to show material and morphological changes at the surface. Such microspheres are used as whispering gallery mode cavities for micro-sensors, for devices in optical communications and, with rare earth doping, for micro-lasers. It is the optical quality of the glass at, and near, the surface, that is most important in these applications. With the surface corrosion shown, the Q of a whispering gallery mode resonator based on such a microsphere will reduce dramatically over time. More generally, the result may have significant implications for the production, storage, and usage of uncoated chalcogenide micro-optics. The FIB technique emerges as an additional tool for characterizing glass morphology and homogeneity. 2012-08-10T12:11:16.241Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:19313 Refractive-index measurements of spider silks using image-contrast immersion methods are presented, with a precision twenty times greater than has previously been attained. Dispersion and birefringence measurements of the spider silks are also realised. 2012-05-23T21:35:28.831Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:19388 A variety of dynamical outputs can be generated with an optically injected solid state laser by varying the intensity of the injection from the master into the slave laser, and/or the frequency detuning between the master and slave lasers. The system is capable of generating regular laser pulses with constant amplitude and robust period, as well as irregular pulses with chaotically varying amplitude. We propose that a mapping of the variation in interpulse duration of an optically injected solid state laser is a useful tool to facilitate identification of different dynamical regions within the parameter space. 2012-05-23T21:30:26.277Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:19267 Focussed ion beam milling, combined with secondary ion and secondary electron imaging, is used to evaluate internal imperfections in glass microspheres. Flaws on the nano-scale and micro-scale are exposed. Glass aging can also be characterised. 2012-05-23T00:20:54.792Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:18761 AFM (Atomic Force Microscopy) and OSP (Optical Surface Profiling) have been applied to measure the surfaces of spider silks – both radials and capture silks- at the nano- and micro-scale. 2012-04-20T05:42:16.944Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:18762 Relaxation Oscillation Frequency (ROF) as a function of current is a key parameter of quantum well lasers. Here we apply a new technique to study the ROF at high injection currents where ROFs are very heavily damped. 2012-04-20T05:42:08.053Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:14880 An optically injected solid state laser (OISSL) system is known to generate complex nonlinear dynamics within the parameter space of varying the injection strength of the master laser and the frequency detuning between the master and slave lasers. Here we show that within these complex nonlinear dynamics, a system which can be operated as a source of laser pulses with a pulse repetition frequency (prf) that can be continuously varied by a single control, is embedded. Generation of pulse repetition frequencies ranging from 200 kHz up to 4 MHz is shown to be achievable for an optically injected Nd:YVO4 solid state laser system from analysis of prior experimental and simulation results. Generalizing this to other optically injected solid state laser systems, the upper bound on the repetition frequency is of order the relaxation oscillation frequency for the lasers. The system is discussed in the context of prf versatile laser systems more generally. Proposals are made for the next generation of OISSLs that will increase understanding of the variable pulse repetition frequency operation, and determine its practical limitations. Such variable prf laser systems; both low powered, and, higher powered systems achieved using one or more optical power amplifier stages; have many potential applications from interrogating resonance behaviors in microscale structures, through sensing and diagnostics, to laser processing. 2011-11-09T03:17:49.612Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15862 A technique for measuring the refractive index of micron sized fibers using a series of immersion index matching oils, and image contrast measurements is proposed and demonstrated. It has been applied to radial silks of the orb web weaving spider Plebs eburnus. These have widths of ∼1-2 microns. Values about 1.5500 are obtained, with birefringence values between 0.0000 and 0.0133 for individual silks. An uncertainty in the range ± 5 × 10 -4 to ± 2 × 10-3 is achieved for these challenging samples. This accuracy is about a twenty times improvement on previously reported measurements for spider silks using other techniques. The technique is used to obtain measurements of the refractive index of spider silks as a function of wavelength, for the first time. An Abbe number for the radial silks of Plebs eburnus of ∼32 is found. 2011-11-09T03:11:52.756Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12307 Atomic force microscopy (AFM) study is used to measure the surface topology and roughness of radial and capture spider silks on the micro- and nanoscale. This is done for silks of the orb weaver spider Argiope keyserlingi. Capture silk has a surface roughness that is five times less than that for radial silk. The capture silk has an equivalent flatness of λ/100 (5–6 nm deep surface features) as an optical surface. This is equivalent to a very highly polished optical surface. AFM does show the number of silk fibers that make up a silk thread but geometric distortion occurs during sample preparation. This prevented AFM from accurately measuring the silk topology on the microscale in this study. 2011-03-24T13:20:48.381Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:4198 In earlier work we characterised single-pulse laser cleaning of medium-density (areal coverage 10–20%) alumina particles from glass surfaces with three different lasers. The method of measuring particle-removal efficiency involves optical microscopy imaging (digital) and subsequent image analysis of the area covered by, and/or the number of, particles before and after the single-pulse laser cleaning treatment. The sample-preparation technique used leads to both single particles and agglomerates on the surface. The issues of depth of focus in the imaging and grey-scale thresholding in the image analysis of such samples, with a range of particle and agglomerate sizes, has been systematically investigated. A protocol for optimum imaging and illumination of such samples is described herein. It has been developed based on the results of a systematic investigation of the effect of the image focal plane position relative to the surface also described herein. The image analysis to quantify the particles on the surface involves a judgement of the best threshold grey-scale level in the image to define the boundary between particles and background substrate. A quantitative appraisal of the impact on the laser cleaning efficiency results of a threshold grey-scale level that is set too high or too low, and how these results compare with those obtained for the "best-judgement" threshold grey-scale level, has been completed. 2011-02-03T04:06:13.727Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11417 We have investigated the scaling of peak vacuum ultraviolet output power from homogeneous Xe dielectric barrier discharges excited by short voltage pulses. Increasing the Xe fill pressure above 1 bar provides an increased output pulse energy, a shortened pulse duration and increases in the peak output power of two to three orders of magnitude. High peak power pulses of up to 6 W cm⁻² are generated with a high efficiency for pulse rates up to 50 kHz. We show that the temporal pulse characteristics are in good agreement with results from detailed computer modelling of the discharge kinetics. 2011-01-21T03:20:29.294Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:1503 Chaos data analysis has been performed on the chaotic output power time series data from a synchronized transmitter–receiver pair of semiconductor lasers. The system uses an asymmetric, bidirectional coupling configuration between the master (transmitter), which is a laser diode with optical feedback, and a standalone slave semiconductor laser. The correlation dimension of the chaotic time series has a minimum value of 4, which was obtained from high-bandwidth measurements. The correlation dimensions for both the master and the synchronized slave are identical when the cross-correlation coefficient of the synchronized chaos is above 0.9. These results establish correlation dimension analysis as an effective tool for the determination of the quality of wideband chaos synchronization. 2011-01-17T06:13:27.885Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:8650 Nonlinear lasers are excellent systems from which to obtain high signal-to-noise experimental data of nonlinear dynamical variables to be used to develop and demonstrate robust nonlinear dynamics analysis techniques. Here we investigate the dynamical complexity of such a system: an optically injected Nd:YVO4 solid state laser. We show that a map of the correlation dimension as a function of the injection strength and frequency detuning, extracted from the laser output power time-series data, is an excellent mirror of the dynamics map generated from a theoretical model of the system. An automated computational protocol has been designed and implemented to achieve this. The correlation dimension map is also contrasted with prior research that mapped the peak intensity of the output power as an experimentally accessible measurand reflecting the dynamical state of the system [Valling et al., Phys. Rev. A 72, 033810 (2005)]. 2011-01-17T05:01:22.157Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:9177 The electrical and optical characteristics of a dielectric barrier discharge (DBD) based neon excimer lamp generating output in the extreme ultraviolet (EUV) spectral range (λ=84nm) have been investigated experimentally. We report a detailed comparison of lamp performance for both pulsed and sinusoidal voltage excitation waveforms, using otherwise identical operating conditions. The results show that pulsed voltage excitation yields a ~50% increase in the overall electrical to EUV conversion efficiency compared with sinusoidal waveforms, when operating in the pressure range 500–900 mbar. Pulsed operation allows greater control of parameters associated with the temporal evolution of the EUV pulse shapes (risetime, instantaneous peak power). The Ne DBD based source is also found to be highly monochromatic with respect to its spectral output from the second continuum band at λ ~ 84 nm (5 nm FWHM). This continuum band dominates the spectral emission over the wavelength range 30–550 nm. Lamp performance; as measured by the overall EUV output energy, electrical to EUV conversion efficiency and spectral purity at λ ~ 84 nm; improves with increasing gas pressure up to p = 900 mbar. 2010-08-11T10:30:22.437Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:8821 The soft turn-on of semiconductor lasers leads to uncertainty in defining and measuring the laser threshold injection current, I th. Previously, practical calculation algorithms have been developed to achieve high-accuracy measurement of a clearly defined and reproducible quantity which is called I th. We demonstrate a new and higher accuracy measurement of I th using the dependency of the relaxation oscillation frequency on injection current, as compared to the existing standardized approaches. Further, if it is accepted that relaxation oscillations do not occur below laser threshold, this may be regarded as a more fundamentally based definition and measurement method to determine the laser threshold injection current in a semiconductor laser. The method may also be applicable to other types of lasers. 2010-07-01T18:50:25.577Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:1661 The 'clean' surface of silica glass is usually covered with a quasi-layer of hydroxyl groups. These groups are significant as their concentration on a surface affects surface adhesion and chemical reactivity. Removal of hydroxyl groups from the surface by a UV pulsed laser treatment has been demonstrated to be an alternative technique to the dehydroxylation of glass by the traditional oven heat treatment. Silica so treated has improved resistance to particulate adhesion. Dehydroxylation using this UV laser treatment has key advantages of being: a much faster process; largely limited to heating the surface not the bulk of the silica; and which allows selective spatial patterning of the dehydroxylation of the silica surface. This work outlines a technique developed to allow systematic, quantitative measurements of the dehydroxylation of UV fused silica. The removal of hydroxyl groups using laser irradiation is shown to be a thermal process. 2010-01-27T23:13:44.770Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:1662 An overview of the literature on laser cleaning experiments is provided in a tabulated form. The details of a large cross-section of experimental studies on the removal of particles and contaminants from various material surfaces by pulsed laser cleaning is provided and discussed. The tables aim to provide a useful, clear and quick comparison of the numerous different sets of experimental parameters used in laser cleaning studies, and to enable a better understanding of the removal of particulates from surfaces. 2010-01-27T23:13:43.595Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:1663 Laser Cleaning II is the second of a series of books reporting research on the use of lasers for cleaning material surfaces and related micro-scale and nano-scale laser processing. It follows Laser Cleaning, edited by Boris Luk’yanchuk, published in 2002. The primary focus is on contaminant particle removal, nano-scale sized particles in particular, which represents a major cleaning challenge in industrial contexts and poses a broad range of research questions. The contributions provide stimulating answers to these questions, spanning the essential areas: the fundamental theoretical and experimental physics of light/particle/interface interactions, invention and development of laser cleaning techniques and diagnostics, simulations for important material and process systems, and laser cleaning and processing applications. Laser cleaning for art and cultural heritage conservation is a related, mature field of research which is also treated. 2010-01-27T23:13:43.275Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:1727 Short pulsed, high peak power VUV output has been obtained from pulsed voltage excitation of high pressure dielectric barrier discharges (DBD). Output with these characteristics has demonstrated advantage over longer pulse DBD VUV sources for several materials processing and surface modification applications. Results using a Xₑ₂* DBD source at 172 nm for removing optical mountants from optical surfaces, for removing hydrocabon contamination from optical and polymer surfaces, and dehydroxylation of fused silica are presented. Guidelines. 2010-01-27T23:13:04.560Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:1728 Laser cleaning of 5.0μm diameter silica spheres from silica surfaces was investigated. It was found that for three different slide preparation methods that the particles did not adhere strongly to the silica surface. Experimental laser cleaning particle removal thresholds were 4 orders of magnitude less than that predicted by theoretical modelling based on thermal expansion and Van der Waals force. This is supported both by the present study which found that silica spheres did not adhere strongly to silica slides for three different preparation methods and by previous atomic force microscope (AFM) and surface force apparatus (SFA) studies which showed the existence of a short range repulsive force between silica spheres and silica substrates. The second explanation is that the spheres have a greater effective absorption coefficient than that of bulk silica. This was supported by the fact that at high fluences small hillocks of silica remained after irradiation indicating that temperatures in excess of 1900 K had been achieved. Both factors taken together can account for the discrepancy between theoretical predictions and experimental results in the present study. 2010-01-27T23:13:04.554Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:1763 A direct means for determining the optimum frequency modulation frequency for enhanced frequency-shifted feedback laser ranging is reported. 2010-01-27T23:12:39.387Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:2088 48 page(s) 2010-01-27T23:08:20.898Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:3216 The effect of micro-particle shape on the laser – irradiation-field forward transmitted in a particle-on-a-surface system, and the resulting differences in processing, are reported. 2010-01-27T22:55:34.883Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:3223 Developments in measurement equipment bandwidth and memory have allowed standard chaotic time series analysis of the multi-GHz output power fluctuations of a semiconductor laser operating chaotically. An investigation into the effect of noise shows the degradation of this analysis at low signal-to-noise ratios. 2010-01-27T22:55:29.205Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:3645 The output state of a broad-area diode (BAD) laser with phase conjugate feedback (PCF) from Rh:BaTiO₃ crystal is compared to the same diode laser with conventional optical feedback from a plane mirror. A number of distinct output states, including low frequency fluctuations, are observed for each feedback type. Stable single spectral mode output is achieved with phase conjugate feedback above an injection current dependent critical level (~20%). Conventional optical feedback from a plane mirror does not induce single-mode output at any feedback level. 2010-01-27T22:50:44.319Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:3730 The frequency of relaxation oscillations in a heavily damped quantum well laser, as a function of injection current, have been measured with an accuracy as good as 0.3% using a new method involving averaging of many, real-time, individual, relaxation oscillation events. This accuracy represents at least a six fold improvement compared to that obtained by the standard RF spectral analysis method applied to the same system. This accuracy enables critical comparison of experimental results with standard theory and suggests systematic variation of the experimental values from expected theory. This motivates further developments in the theory of relaxation oscillations in quantum well semiconductor lasers. 2010-01-27T22:49:46.071Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:3732 Irradiating silica microspheres, on a silica or glass surface, with single, high-energy, laser pulses from a KrF excimer laser, has generated a wealth of different micron and sub-micron, topological patterns in the substrate. Optical surface profilometry has been used as the experimental technique to study the patterns formed. Comparison of the experimental results with theoretical results from sophisticated models developed by Lukyanchuk and co-workers, and Arnold and co-workers is presented. 2010-01-27T22:49:44.763Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:3777 A broadband multi-mode output with optical frequency bandwidth of several THz has been obtained by a method of modulating a two-section semiconductor laser (TSL). The comb-of-modes output can be systematically varied in bandwidth and opens up a new range of applications for TSLs. 2010-01-27T22:49:12.875Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:3776 An overview is given of recent achievements of the Materials Processing Branch of the Short Wavelengths and Interactions with Materials (SWIM) program at Macquarie University. This research focuses on using shortpulsed UV lasers and other novel W sources to clean small particles (including sub-micron particles) and hydrocarbons 6om optical, optoelectronic and photonic materials. 2010-01-27T22:49:12.836Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:3778 Further advances have been made in the development and understanding of an ultraviolet (UV) laser treatment of fused silica glass. Hydroxyl groups present on the surface can be removed by the treatment. The surface hydroxyl groups affect the surface adhesion and performance of silica in catalysis, chromatography, photonics and microelectronics. This work shows that dehydroxylation via laser irradiation is a thermal process. An analysis technique using mass spectrometry has been developed to elucidate and avoid the effect of hydrocarbon contamination, allowing systematic measurements of dehydroxylation to be performed. 2010-01-27T22:49:11.197Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:4153 A calculation is performed of the quantum noise penalty which is incurred due to nearest-neighbour inter-element coupling in laser diode arrays. The use of suitable assumptions allows the derivation of a simple closed-form expression which allows quantification of the noise penalty as a function of the strength of the inter-element coupling. The opportunity for fabricating optimised low-noise optical pumps based on laser diode arrays is identified. 2010-01-27T22:44:44.641Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5219 A fluence advantage was achieved in dry/damp laser cleaning by reduction of the laser beam dimensions. 0.1 μgrm Al₂O₃ particles were removed from glass slides using a KrF excimer laser (248 nm). As the width of the rectangular beam was reduced, a decrease in the threshold fluence required for particle removal was observed. Modelling based on the simplified thermal–mechanical response of the substrate and particle to the laser pulse does not describe the experimental results presented here. The case of dynamic expansion must be further considered, but it is believed that other mechanisms are involved in a full explanation. 2010-01-27T22:32:56.476Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5520 We report a detailed experimental and modeling study of efficiency for dielectric barrier discharge excited lamp containing mixtures of xenon and iodine. A survey of performance as functions of pressure, iodine partial pressure and excitation parameters indicates that the maximum efficiency of conversion from electrical output to UV (253nm) is in the range 1-2% in contrast to previous reports of efficiency > 20% [eg. Zhang and Boyd, J. Appl. Phys 84, 1174 (1998)]. The results are in good agreement with a 1-D rate-equation model of the discharge kinetics, which suggests that direct quenching of the upper states of the Xel* (B-X) transition (253nm) by I₂ limits the output efficiency. 2010-01-27T22:29:47.744Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5879 Waxes and thermopolymers are commonly used to mount optical and photonic materials prior to polishing and singularization. After demounting, residual wax/thermopolymer can adhere to the component surface, frequently in the form of particles. Dry, ultraviolet-pulsed laser cleaning has been demonstrated to effectively remove paraffin wax particles, prepared on a glass surface using a wax aerosol technique. This method produces dome-shaped particles. Experimental evidence suggests the dome-shaped particles are vaporized by the absorption of the energy from the laser pulse. A theoretical model based on vaporization has been developed and this leads to predictions of the critical fluence for single laser pulse removal of dome-shaped particles which is in good agreement with that experimentally measured (220 mJ/cm²). The model also gives insight into the geometries and relative thermal properties of the "particles" and surface, which are important in determining whether removal by vaporization is a viable process 2010-01-27T22:25:12.177Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5880 Silica and microscope slides that had been pretreated with a variety of wet chemical, ultrasonic and laser irradiation surface preparation methods were contaminated with alumina particles of around 3 µm. The samples were prepared and processed without delay so as to avoid capillary condensation in a high humidity environment and thus ensuring that the process is dry laser cleaning. They were then irradiated with a pulse of 248 nm radiation from a KrF excimer laser, over a range of fluences. The laser cleaning results show that, in this case, the surface preparation method appears to have little effect on the laser cleaning efficiency. They also demonstrate that the threshold fluence for particle removal of silica is approximately eight times higher than that for microscope slides, when so prepared. In contrast, application of Arnold et al.'s thermal expansion model of laser cleaning in the quasistatic limit to this material system predicts that the threshold fluence for silica will be about 15 times greater than that for glass. One possible explanation for this discrepancy may be that the particle's absorptivity (0.16) is inaccurate. A value of 0.35 gives good agreement between theory and experiment. 2010-01-27T22:25:12.132Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:6533 Prior research in the field of laser cleaning has suggested that shorter pulses are preferable to achieve low laser cleaning threshold fluences. These predictions were based mainly on exponential pulse shapes In the present work the three-dimensional model of laser cleaning developed by Boris Luk'yanchuk (B. S Luk'yanchuk et al., Appl Phys A, 77,2,209) which accounts for near-field focussing, has been used to calculate the laser cleaning threshold fluence for three different pulse shapes These were rectangular, sinusoidal and exponential For each pulse shape, the threshold fluence was determined as a function of pulse width (1- 200 ns) and height (1-15 GW/cm²). It was found that the threshold fluence is strongly dependent on the laser pulse shape, particularly for pulses greater than 100 ns in width. The threshold fluence of the rectangular pulse oscillated with a period equal to that of the period of oscillation of the particle on the substrate. In contrast, for both the exponential and sinusoidal pulses, the threshold fluence increases monotonically with pulse length. 2010-01-27T22:16:40.180Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:6534 Optical surface profilometry is a technique that has advantages over other profilometry techniques (stylus profilometry, AFM) of being non-contact and being able to profile comparatively large areas in a single "z-scan". Thus, it is employed in monitoring surface quality and measuring surface form in high technology manufacturing processes and quality assurance, as well as being applied as a diagnostic in research and development contexts. Its application to optical materials has been limited due to issues relating to the low reflectance of the surfaces. A feasibility study for profiling laser induced optical damage and "loose" microscopic sized pieces of optical material (particles introduced by design) on optical substrates is reported. Progress on profiling these difficult samples has been achieved. 2010-01-27T22:16:38.947Z ]]>