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: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:18506 We present a parametric study of self-assembled photonic crystal growth as a function of radius of curvature. To do this, we used a combination of microscope slides, glass capillaries and optical fibres as substrates to grow the self-assembled films on. Microscope and SEM images, as well as broadband transmission spectra were used to characterise the crystal, and the effect the changing surface curvature had on the crystal quality. Limitations for fabricating the crystals on highly curved surfaces will be presented. 2012-04-03T20:30:23.710Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:17549 4 page(s) 2012-02-11T06:30:05.799Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:16395 We report on the development of a compact, all fibre laser source operating at 1 μm with a linearly polarized (extinction ratio > 20 dB) and very narrow linewidth (12 pm) output. The unique cavity design included a fibre Bragg grating high reflector and output coupler, inscribed via the point-by-point method directly into the active core. A single splice within the cavity between the fibre incorporating the high reflector and the output coupler permitted re-orientation of the stressors at an angle of 90 degrees to each other, which produced a single lasing polarisation. This simple technique removed the need for a more complicated and expensive polarization controller. 2011-12-21T19:31:21.148Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:16396 We have performed measurements using a purpose-built Near-field Scanning Optical Microscope and shown that waveguides written with a fs laser in the kHz regime have an asymmetry associated with the unidirectional nature of the writing beam. Further, the asymmetry becomes more pronounced with increasing pulse energy. At very high pulse energies (5-10 J) the presence of multiple guided regions was also observed, indicating that the refractive index profile of the waveguide possesses several maxima, a result which is consistent with current studies on the filamentation process that high-powered laser pulses experience in a dielectric medium. In this paper we will present these observations, their subsequent analysis and implications for photonic device fabrication using this method. 2011-12-12T03:40:13.857Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:16397 We demonstrate resonant guiding in a chalcogenide glass photonic crystal membrane associated with Fano coupling between free space and guided modes. We obtain good agreement with modeling results based on three-dimensional finite-difference time-domain simulations. 2011-12-12T03:40:12.529Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:16041 An injection-seeded, self-adaptive optical parametric oscillator cavity with a photorefractive phase-conjugate reflector generates tunable nanosecond-pulsed output. Its narrow, single-longitudinal-mode optical bandwidth is verified by high-resolution spectroscopic measurements. 2011-11-21T23:10:44.164Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15972 We taper a 90% air-fill, air core, photonic crystal fiber and observe a multitude of partial band gaps along the taper length. We simulate this geometry with the FDTD and plane wave expansion methods. 2011-11-17T16:51:52.564Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15974 We present a general scheme to trap slow-light in a photonic crystal slab and achieve high Q/V ratio with a fabrication tolerant design, well suited for low-threshold microlasers and cavity quantum electrodynamics. 2011-11-17T16:51:45.873Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15976 We design novel photonic crystal slab heterostructures, substituting the air in the holes with liquid crystal, polymer or nano-porous silica. We demonstrate numerically that such cavities can have quality factors up to Q=10⁶. 2011-11-17T16:51:37.409Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15963 We experimentally and numerically investigate femtosecond pulse propagation in high index inclusion microstructured optical fibers, which feature both, a resonant dispersion with strong wavelength dependence and a high nonlinearity. 2011-11-15T18:10:22.022Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15965 In this paper we present the first demonstration of femtosecond pulse propagation in ARROW (anti-resonant reflecting optical waveguide) type photonic crystal fibres (PCFs). These are solid core PCFs in which the cladding is composed of high rather than low index cylinders, which can be realized by drawing a high index fluid into the air holes of a commercially available microstructured fibre. 2011-11-15T18:10:16.812Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15420 We report an all-solid-state Raman laser with intracavity frequency mixing, which can be easily configured (without exchanging optics) to switch between various wavelengths in the range 532nm-606nm, with average powers of up to 2W. 2011-10-14T13:10:34.683Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:15250 We describe the operation of an all solid-state pulsed dye laser of high repetition rate (10 kHz) pumped by a diode-pumped laser. Three different active media in the form of coin-sized disks were investigated: the dye rhodamine 6G doped in a copolymer of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) [Rh6G/P(MMA:HEMA)], and the dye pyrromethene 567 (PM567) doped in copolymers of MMA with pentaerythritol triacrylate (PETA) and with pentaerythritol tetraacrylate (PETRA) [PM567/P(MMA:PETA) and PM567/P(MMA:PETRA)]. Pump radiation at 527nm was provided by a frequency-doubled diode-pumped Nd:YLF laser Q-switched at 10 kHz. Laser output was observed with an initial average power of 560 mW for Rh6G in P(MMA:HEMA), and with an initial average power of 430 mW for PM567 in P(MMA:PETRA) and 220 mW for PM567 in P(MMA:PETA). In the case of Rh6G/P(MMA:HEMA), the output decreased to about half the initial value after about 6.6 min (or about 4.0 million shots) due to dye degradation. The device constitutes a tunable, all solid-state, high repetition rate laser system possibly suitable for biomedical and dermatological applications. 2011-10-05T13:10:15.854Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:14548 38 page(s) 2011-08-17T23:00:37.194Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:14220 By using a CW mode-locked 532 nm laser to synchronously pump a crystalline Raman laser, we can generate output in the yellow-orange spectral region, suited to applications requiring low pulse energies and continuous pulse trains. We demonstrate a synchronously pumped Raman laser at 559 nm, pumped by a frequency-doubled mode-locked Nd:YVO₄ commercial laser. The generated CW mode-locked output had an overall (green-yellow) efficiency of 25.6%, and we observed a compression of the 10 ps pump pulses down to 3.2 ps at 559 nm. This compression was observed when the cavity length was slightly longer than for perfect synchronization. 2011-08-01T06:24:47.940Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:14221 In this paper, we will show results of the first quasi-cw and mode-locked output from a Ce:LiCAF laser, opening the way to a new approach to generating attosecond pulses using three mirror cavity. The 1.25 mm-long cerium crystal was synchronously pumped by a quadrupled mode-locked Nd:YAG laser. The pump was chopped to avoid thermal effects in the doubling crystals. By matching the cavity lengths of the pump and cerium laser, picosecond mode-locked operation was achieved at 290 nm. 2011-08-01T06:24:45.057Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:14244 We study waveguide writing in various transparent dielectric materials using a highly flexible chirped-pulse femtosecond oscillator (CPO) as the laser source. This unique device allows us to investigate an unprecedented parameter range up to 5.2 MHz in repetition rate, 50 fs-2 ps in pulse duration and up to 600 nJ in energy per pulse. Thus the CPO closes the gap between high energy amplifier- and high repetition oscillator-direct waveguide writing. 2011-08-01T06:24:00.351Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:14063 We present a diode-pumped Yb³⁺: YAl₃(BO₃)₃ (Yb:YAB) laser system and measured the polarized outputs of the CW and femtosecond mode-locked lasers with semiconductor saturable-absorber mirrors (SESAM) at the fundamental wavelength. For the CW output, polarization ratios were 88.1% and 87.2% . For the mode-locked system, polarization ratio reached 38.5%. 2011-07-08T12:11:46.230Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:14038 Low birefringence synthetic single-crystal diamond was used as a Raman laser medium inside a Q-switched Nd:YVO₄ laser. A maximum average output power of 375mW was achieved at a wavelength of 1240nm and a repetition rate of 6.3kHz. This equates to a conversion efficiency of 4% from the diode laser to the first Stokes component at 1240nm. Optical losses within the diamond (~1% per single pass) limited the performance and are currently the main barrier to the demonstration of an efficient CW diamond Raman laser. 2011-07-07T05:41:08.474Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13599 Many naturally occurring materials are autofluorescent, a property that can reduce the discriminative ability of fluorescence methods, sometimes to the point where they cannot be usefully applied. Shifting from the spectral to the temporal domain, it is possible to discriminate fluorophores on the basis of their fluorescence decay lifetime. Luminophores with sufficiently long lifetimes can be discriminated from short-lived autofluorescence using time-gated luminescence (TGL). This technique relies upon the application of a brief excitation pulse followed by a resolving period to permit short-lived autofluorescence to decay, after which detection is enabled to capture persistent emission. In our studies, a high-power UV LED was mounted in the filter capsule of an Olympus BX51 microscope to serve as the excitation source. The microscope was fitted with an Andor DV885 electron-multiplying CCD (EM-CCD) camera with the trigger input synchronized to UV LED operation. Giardia lamblia cysts labeled with the europium chelate BHHST were analyzed against an autofluorescent background with the TGL microscope. The EM-CCD camera captured useful TGL images in real time with a single exposure cycle. With 4x frame averaging, images acquired in TGL mode showed a 30-fold improvement in SNR compared with conventional fluorescence microscopy. 2011-06-10T10:30:45.420Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13602 The ubiquity of naturally fluorescing components (autofluorophores) encountered in most biological samples hinders the detection and identification of labeled targets through fluorescence-based techniques. Time-resolved fluorescence (TRF) is a technique by which the effects of autofluorescence are reduced by using specific fluorescent labels with long fluorescence lifetimes (compared with autofluorophores) in conjunction with time-gated detection. A time-resolved fluorescence microscope (TRFM) is described that is based on a standard epifluorescence microscope modified by the addition of a pulsed excitation source and an image-intensified time-gateable CCD camera. The choice of pulsed excitation source for TRFM has a large impact on the price and performance of the instrument. A flash lamp with rapid discharge characteristics was selected for our instrument because of the high spectral energy in the UV region and short pulse length. However, the flash output decayed with an approximate lifetime of 18 μs and the TRFM required a long-lived lanthanide chelate label to ensure that probe fluorescence was visible after decay of the flash plasma. We synthesized a recently reported fluorescent chelate (BHHCT) and conjugated it to a monoclonal antibody directed against the waterborne parasite Giardia lamblia. For a 600-nm bandpass filter set and a gate delay of 60 μs, the TRFM provided an 11.3-fold improvement in the signal-to-noise ratio (S/N) of labeled Giardia over background. A smaller gain in an SNR of 9.69-fold was achieved with a 420-nm longpass filter set; however, the final contrast ratio between labeled cyst and background was higher (11.3 versus 8.5). Despite the decay characteristics of the light pulse, flash lamps have many practical advantages compared with optical chopper wheels and modulated lasers for applications in TRFM. 2011-06-10T10:30:26.343Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13554 Intracavity nonlinear second harmonic generation from a Q-switched, diode-end-pumped Nd:YVO4 laser (1342nm) and subsequent external fourth harmonic generation in BBO have been used to demonstrate up to 20mW average power at 336nm at multi-kilohertz repetition-rates. 2011-06-09T03:10:46.384Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13471 Geoffrey Blainey has long been one of Australia's most prominent, and at times controversial historians. Apart from his usual focus on Australian history, his primary work concerning international politics has been his book 'The Causes of War', making him one of the more notable Australian contributors to issues of war and peace in the field of international relations. His theory on the causes of war is based on an implicit rational actor model of perceptions of military power. His hypothesis is: When two sides disagree on their relative strength, war is likely. When they agree, peace is likely. With case studies on the wars in Nagorno-Karabakh and Sierra Leone, this book considers whether Blainey's hypothesis on war, which was designed to analyse international wars, remains applicable to contemporary internal wars. Blainey's ambition was to come up with a general theory on why wars begin and conclude. Before claiming that his theory is truly comprehensive, and still relevant, it needs to be tested against the dominant form of warfare today; internal, or intrastate wars. 2011-06-03T05:00:46.262Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13452 5 page(s) 2011-06-02T01:00:07.806Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13441 Direct-diode pumping of Nd-based laser materials at 880 nm offers reduced thermal loading and improved system stability. In this paper we compare absorption properties of Nd:GdVO₄, Nd:YVO₄ and Nd:KGW at 808 nm and 880 nm, and we report improvements in the performance of a high-Q, high-power self-Raman laser in Nd:GdVO₄,pumped at 879 nm. 2011-05-31T09:20:07.989Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13335 CW single-longitudinal-mode output in the 1120-1140 nm range and self-frequency-doubling into the yellow spectral region has been observed in Yb:YAB, Excellent agreement between experiment and modelling of yellow output in a single-crystal solid-state-laser system is observed. 2011-05-27T04:32:23.994Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13343 This paper presents experimental and theoretical studies of time-gated discrimination of long-lived luminescence (lifetime: 1~2000μs) labelled target-organisms against non-target autofluorescence background (lifetime: <100 ns) in flow cytometry. A theoretical model of such a TGL flow cytometer is developed which takes account of flow speed, illumination and detection apertures, fluorescence label lifetime, and pulsed illumination and gated detection timing sequences. Ultraviolet LED and channel photomultiplier were found to be practical as pulsed excitation sources and gated detector for TGL flow cytometry. The prototype cytometer was constructed and optimized to operate at 6 k Hz repetition rate of TGL cycles consisting of 100 μs LED excitation and ~60 μs gated detection. The spatial counting efficiency was evaluated by enumerating 5.5 μm diameter europium microspheres resulting in a counting accuracy approaching 100%. 2011-05-27T04:31:53.752Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13359 Effective sensing with photonic crystal cavities requires optimization of modal quality factor and field overlap. For several unrelated cavities, we find the quality factor dominates, so that dielectric modes are strongly favored over air modes. 2011-05-27T04:31:06.710Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12367 This paper report a CW, frequency doubled, Nd:GdV04 self-Raman laser producing 2.51 W of CW yellow emission with a 12.2 % overall optical (diode-to-yellow) conversion efficiency. This high level of output power is a result of a laser design which minimises thermal loading of the laser crystal, minimises resonator loss at the fundamental and first Stokes wavelength and maximises the collection efficiency of the yellow light generated in the doubling crystal. 2011-05-25T22:12:23.975Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12731 A new compact configuration of a printed CPW-fed semicircular slot antenna with a CPW-to-CPW step transition is presented. Its bandwidth is enhanced for ultra-wideband (UWB) operation by combining linear and stepped CPW-to-CPW transitions along the feed line. Its measured 10 dB return loss bandwidth is 3.1–13.8 GHz (126%). This, together with its nearly constant measured gain of 3.5 dBi ± 1 dB from 3 to 10 GHz, makes it suitable for UWB applications. Details of the proposed antenna are described, and both theoretical and experimental results are presented. 2011-05-25T22:03:25.293Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12744 We summarize our recent research in Raman lasers based on undoped single crystal diamond. Highly efficient visible external cavity lasers operating in nanosecond and picosecond regimes are reported. 2011-05-25T22:02:52.063Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12760 An ultra-wideband printed monopole antenna, improved by attaching a short two-plate horn to its surface, is reported in this paper. The short horn, which has a slant length of 45 mm and a total physical height of 46.9 mm, significantly increases the gain of the printed monopole antenna at lower frequencies where the gain of the monopole is otherwise low, giving an almost flat gain over a 114 % bandwidth. The new antenna has a measured gain in the range of 4.8 dBi ± 0.7 dB from 3 GHz to 12 GHz. Due to its compact configuration, ease of fabrication, high gain, broad azimuth pattern and minimal ringing of a radiated pulse, it is suitable for UWB applications. 2011-05-25T22:02:20.362Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12767 Zinc oxide (ZnO-nano) and titanium dioxide nanoparticles (20 to 30 nm) are widely used in several topical skin care products, such as sunscreens. However, relatively few studies have addressed the subdermal absorption of these nanoparticles in vivo. We report on investigation of the distribution of topically applied ZnO in excised and in vivo human skin, using multiphoton microscopy (MPM) imaging with a combination of scanning electron microscopy (SEM) and an energy-dispersive x-ray (EDX) technique to determine the level of penetration of nanoparticles into the sub-dermal layers of the skin. The good visualization of ZnO in skin achieved appeared to result from two factors. First, the ZnO principal photoluminescence at 385 nm is in the “quiet” spectral band of skin autofluorescence dominated by the endogenous skin fluorophores, i.e., NAD[P]H and FAD. Second, the two-photon action cross section of ZnO-nano [σZnO(TPEF) ∼ 0.26 GM; diameter, 18 nm] is high: ∼ 500-fold of that inferred from its bulk third-order nonlinear susceptibility [Im χZnO⁽³⁾], and is favorably compared to that of NAD[P]H and FAD. The overall outcome from MPM, SEM, and EDX studies was that, in humans in vivo, ZnO nanoparticles stayed in the stratum corneum (SC) and accumulated into skin folds and/or hair follicle roots of human skin. Given the lack of penetration of these nanoparticles past the SC and that the outermost layers of SC have a good turnover rate, these data suggest that the form of ZnO-nano studied here is unlikely to result in safety concerns. 2011-05-25T22:02:05.310Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12811 A miniature fiber optic spectrometer enclosed within a semipermeable (dialysis) membrane is proposed for in vivo interstitial sensing applications. The semipermeable membrane acts as a molecular filter, allowing only small molecules to pass through to the sampling volume. This filtering, in principle, should enable continuous in vivo drug sensing, removing the necessity for complex microdialysis systems. We use a biological phantom to examine the reliable detection of a fluorescence signal from small dye molecules in the presence of large fluorophores and scatterers. We find that spectral artefacts arising from scatterers and large fluorophores are substantially suppressed, simplifying the spectral analysis. In addition, the measured sampling rate of 157 s is superior to existing in vivo tissue assaying techniques such as microdialysis, which can take tens of minutes. 2011-05-25T22:00:11.484Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12817 We present a numerical model that explains the pulse compression dynamics occurring in synchronously-pumped Raman oscillators based on transient Stimulated Raman Scattering equations. Excellent agreement is found between our theoretical results and the experimental data. 2011-05-25T21:59:52.081Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12891 The authors have investigated a frequency-doubled passively-Q-switched self-Raman laser formed by a composite Nd:YVO₄/YVO₄ and a saturable absorber Cr:YAG, for the first time. The system is a promising candidate for a compact, cost-efficient pulsed or CW yellow laser source. In future, use of 885 nm diode pumping to reduce thermal lensing may enable further power scaling of the system. 2011-05-25T21:56:56.076Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12912 Femtosecond laser micromachining is a laser processing technology with proven potential for the fabrication of a wide range of photonic devices. In the context of developing integrated components for microfluidics, a key issue is the machining of high aspect ratio micro and nano-channels, and the use of diffraction-free Bessel beams for this purpose has attracted much attention. However, although Bessel beams possess several attractive characteristics for this purpose, we show here that their practical use for high aspect ratio micromachining requires a careful selection of focussing and pump laser parameters. We report results of a systematic study of Bessel beam micromachining of structures of diameter < 5 mum in fused silica, and we describe conditions under which high quality and high aspect ratio structures can be reproducibly obtained. Within the parameter regimes identified here, Bessel beams present quantitative advantages when compared to diffractive Gaussian beams, especially for the drilling of channels of sub-10 mum diameter. Outside this parameter regime, there is little benefit in the Bessel beam approach. 2011-05-25T21:56:07.209Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12943 Crystalline solid-state Raman lasers offer practical and efficient frequency conversion from existing (pulsed) solid-state laser sources which, in combination with SFG, provides for wavelength selection from near-ir to visible and uv at multiwatt average powers. 2011-05-25T21:54:57.381Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12952 1 page(s) 2011-05-25T21:54:34.676Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13002 We report increased wavelength options from Raman lasers for Raman media having two Raman modes of similar gain coefficient. For an external-cavity potassium gadolinium tungstate Raman laser pumped at 532nm, we show that two sets of Stokes orders are generated simultaneously by appropriate orientation of the Raman crystal, and also wavelengths that correspond to sums of the two Raman modes. Up to 14 visible Stokes lines were observed in the wavelength range 555-675nm. The increase in Stokes wavelengths also enables a much greater selection of wavelengths to be accessed via intracavity nonlinear sum frequency and difference frequency mixing. For example, we demonstrate 30 output wavelength options for a wavelength-selectable 271-321nm Raman laser with intracavity sum frequency mixing in BBO. We also present a theoretical analysis that enables prediction of wavelength options for dual Raman mode systems. 2011-05-25T21:51:55.906Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13008 We report on an integrated photonic transmitter of up to 100 MHz repetition rate, which emits pulses centered at 850 nm with arbitrary amplitude and polarization. The source is suitable for free space quantum key distribution applications. The whole transmitter, with the optical and electronic components integrated, has reduced size and power consumption. In addition, the optoelectronic components forming the transmitter can be space-qualified, making it suitable for satellite and future space missions. 2011-05-25T21:51:47.551Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13032 The cell nucleus is the dominant optical scatterer in the cell. Neoplastic cells are characterized by cell nucleus polymorphism and polychromism-i.e., the nuclei exhibits an increase in the distribution of both size and refractive index. The relative size parameter, and its distribution, is proportional to the product of the nucleus size and its relative refractive index and is a useful discriminant between normal and abnormal (cancerous) cells. We demonstrate a recently introduced holographic technique, digital Fourier microscopy (DFM), to provide a sensitive measure of this relative size parameter. Fourier holograms were recorded and optical scatter of individual scatterers were extracted and modeled with Mie theory to determine the relative size parameter. The relative size parameter of individual melanocyte cell nuclei were found to be 16.5 +/- 0.2, which gives a cell nucleus refractive index of 1.38 +/- 0.01 and is in good agreement with previously reported data. The relative size parameters of individual malignant melanocyte cell nuclei are expected to be greater than 16.5. 2011-05-25T21:50:56.977Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13034 We report on a new experimental technique suitable for measurement of light-activated processes, such as fluorophore transport. The usefulness of this technique is derived from its capacity to decouple the imaging and activation processes, allowing fluorescent imaging of fluorophore transport at a convenient activation wavelength. We demonstrate the efficiency of this new technique in determination of the action spectrum of the light mediated transport of rhodamine 123 into the parasitic protozoan Giardia duodenalis. 2011-05-25T21:50:48.408Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13033 We apply the Finite-Difference Time-Domain algorithm to the problem of calculating modal loss in microstructured optical fibers. We use periodic boundary conditions in the longitudinal direction to isolate a mode that decays through transverse perfectly-matched layerboundaries. The loss coefficient is extracted by a direct monitoring of the energy enclosed in the simulation domain. Predictions of the method are compared to results from beam propagation and multipole approaches, and finally the tool is applied to fibers containing elliptical air holes. 2011-05-25T21:50:48.396Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13043 UV LED native luminescence in visible wavelengths was observed to slowly decay. These luminescence properties were investigated providing fundamental understandings in time-resolved fluorescence spectroscopy excited by LEDs instead of nitrogen lasers or xenon flash lamps. 2011-05-25T21:50:32.553Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13048 Efficient intracavity frequency doubling of a q-switched, diode-pumped Nd:YVO₄ laser operating at 1342nm with pulse rates between 40 and 350kHz using type I critically phase matched LBO has been demonstrated. Maximum 671nm output power of 1.7W was obtained at 100kHz, with a diode to red conversion efficiency of 12%. 2011-05-25T21:50:25.071Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13104 A compact antenna with an improved gain is proposed for ultra-wideband (UWB) systems. A semicircular slot antenna fed by a CPW to CPW transition at the edges of semicircles is employed as the base UWB radiator and a short, two-plate, TEM-like horn is mounted on the surface to enhance the gain over the entire UWB bandwidth. Theoretical and experimental investigations have been conducted to verify the effectiveness of a two-plate short horn as a means for gain enhancement. Experimental results indicate a wide impedance bandwidth from 2.86 to 11.6 GHz and an approximately 3 dB gain enhancement across the band. 2011-05-25T21:48:00.468Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13106 We report a small-scale (10 cm-long) diode-pumped, Q-switched Nd:YVO₄ laser with intracavity (barium nitrate) Raman and (LBO) second-harmonic frequency conversion, generating >100 mW at the 1197 nm first Stokes and 5 mW at the 598 nm frequency-doubled wavelengths for a 1.6 W diode pump. 2011-05-25T21:47:56.700Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13112 Efficient self-stimulated Raman output from a laser diode transversely-pumped Nd³⁺:KGd(WO₄)₂ laser is presented. The maximum Raman output energy of 340 μJ was obtained at 1.18 μm. The corresponding optical efficiency from diode output to the Raman output was estimated to be 2.7%. Yellow output was also generated by intra-cavity second harmonic generation. Up to >90 μJ was obtained. 2011-05-25T21:47:44.556Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13116 Efficient frequency extension of a diode-side-pumped, Q-switched 1064 nm Nd:YAG laser generating ∼5 W at 5 kHz has been demonstrated by way of intracavity SRS in crystalline Ba(NO₃)₂ (1197 nm), KGd(WO₄)₂ (1158 nm and/or 1177 nm), LiIO₃ (1156 nm) and PbWO₄ (1170 nm). 2011-05-25T21:47:36.504Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13120 The allocation of 3.1 GHz to 10.6 GHz spectrum by FCC for ultra-wideband (UWB) communication has motivated the development of UWB antennas, suitable for several applications such as: high data rate terminals (fixed or movable) for multimedia, low data rate system like sensor networks, home entertainment, WLAN, video distribution within cars etc. The sectoral semi-directional antenna with high gain over the ultra wideband has been proposed to improve the system performance by increasing the signal-to- noise ratio and reducing the bit error rate [1]-[2]. 2011-05-25T21:47:31.773Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13118 The polycrystalline material preparation and single crystal growth of Er: Yb: YCa4O(BO3)3(Er: Yb: YCOB) were studied, and the Er: Yb: YCOB single crystals with high optical quality were grown by CZ method successfully. The absorption spectrum and the fluorescence spectrum of Er: Yb:YCOB were measured, and its energy levels and pumping principle were analyzed . The laser experiment of Er: Yb: YCOB crystal pumped by laser diode was performed, and 1.55μm laser output of 110mW was obtained, slope efficiency being 18.9% . 2011-05-25T21:47:29.570Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13121 Microstrip antennas are highly suitable structures for modern communication systems due to their inherent properties like low cost, small size, light weight, easy integration with host surface [1-2]. However their narrow bandwidth and low gain becomes main constraint in their practical applications. In recent times, extensive work for the improvement of bandwidth and gain has been reported [3-4]. The circularly polarized patch antennas are found useful in different communication systems and several circularly polarized patch geometries with improved performance may be seen in available literature on antennas [5-6]. In this communication, a novel antenna design is proposed to achieve circular polarization with much improved impedance bandwidth. 2011-05-25T21:47:24.123Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13122 A coplanar wave guide (CPW) fed semicircular slot antenna (SSA) with step impedance transformer is presented. Omni-directional radiation pattern in whole band with theoretical gain of 3 dBi with variation of plusmn0.5 dB is achieved. It has shown that this design of SSA gives experimental bandwidth of 10.7 GHz for VSWR < 2. Present results show suitability of structure for UWB communication. 2011-05-25T21:47:21.170Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13128 Multi-kilohertz operation at 1497nm and 1528nm has been demonstrated with an Nd:YVO4 laser on the 1342nm transition using intracavity Stimulated Raman Scattering in KGd(WO4)2. Average powers at 1497nm and 1528nm were 200mW and 100mW respectively. 2011-05-25T21:47:07.836Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13155 A constant-gain printed circular monopole antenna (PCMA) is presented that operates from 4 to 12 GHz. The gain of the PCMA is enhanced with the use of surface-wave excited, proximity-coupled (SW-PC), conductor-backed, twin-slot radiators. A significant improvement in 2 and 3 dB peak gain bandwidth in the XY plane (θ = 90°) is achieved, and the peak measured gain of the antenna is nearly constant (5.5 dBi ± 1.5 dB) from 3 to 10 GHz. It has a very broad radiation pattern in the azimuth plane and a typical figure of eight pattern in the elevation plane. The antenna is also compact, robust, and easy to fabricate. 2011-05-25T21:45:49.660Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13203 3 page(s) 2011-05-25T21:43:54.969Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13215 A short linear cavity erbium fiber laser is adapted to become a Q-switched laser by using a new and simple loss switching technique. The technique utilizes the inherent flexibility of optical fiber to rapidly drive the fiber end in and out of alignment with a cavity mirror, creating the conditions necessary for Q-switching. We investigate the effectiveness of different Q-switch configurations and analyze the Q-switch opening time of each configuration. 2011-05-25T21:43:33.995Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13251 There is still significant speculation regarding the nature of femtosecond laser induced index change in bulk glasses with colour centre formation and densification the main candidates. In the work presented here, we fabricated waveguide Bragg gratings in doped and undoped phosphate glasses and use these as a diagnostic for monitoring subtle changes in the induced refractive index during photo- and thermal annealing experiments. Reductions in grating strengths during such experiments were attributed to the annihilation of colour centres. 2011-05-25T21:42:01.326Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13278 A capillary fluorometer was constructed using a 2 mW, 365 nm ultraviolet (UV) light emitting diode (LED) as the excitation source and a new-generation high-gain (3×10⁸) channel photomultiplier tube. The use of a LED permitted rapid pulsing of the excitation source so that the instrument could be employed for time-resolved fluorescence (TRF) applications. A detection limit of ~2×10⁸ molecules of BHHT (4,4’-bis (1",1",1",2",2",3",3"-heptafluoro-4",6"-hexanedion-6"yl)-o-tephenyl)-Eu (III) were resolved within a 1.25 nanoliter volume at a S/N ratio of 3:1. Ultimate sensitivity of the system was compromised due to visible luminescence emitted by the UV LED, centred around 550 nm extending to > 700 nm and 2nd-order exponentially decaying with lifetimes of 40 μs and 490 μs. 2011-05-25T21:40:55.734Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:13283 Ultra-wideband (UWB) technology has been considered for the physical layer in recently proposed IEEE 802.15 standard (TG6) for wireless body area networks. Wireless links covered by this standard will operate in UWB unlicensed band with antennas on implanted devices having small form factors. Except for those installed on-body and on external receivers, the antenna will be operating in-body, surrounded by body tissue. Body tissues have high dielectric constants and are highly dissipative. Once implanted beneath multiple layers of tissue, the device, which is expected to be consuming very low power, experience heavy losses in its transmission and reception path. Therefore, it is essential that antenna losses, both mismatch and resistive, are minimised. In this paper we will demonstrate a method to minimize antenna mismatch losses by loading the antenna with insulating material. 2011-05-25T21:40:36.152Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12414 We report the generation of multi-watt continuous-wave (CW) yellow laser emission from an intracavity diode-pumped Nd:GdVO₄ /BaWO₄ Raman laser utilising a high-Q resonator (for fundamental and first-Stokes wavelengths) and intracavity frequency-doubling in LBO. CW output power of 2.9 W is achieved with a high overall diode-to-yellow conversion efficiency of 11% and with good beam quality (M²~2.5). 2011-04-05T02:50:32.729Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12373 Dielectric rod antennas have advantages as elements of focal plane arrays for imaging applications at terahertz frequencies. As well as good directivity and moderate bandwidth they are readily integrated with diode detectors. To demonstrate these attributes we describe the fabrication of a prototype antenna by laser ablation. Theoretical and measured results are presented for a dielectric rod antenna operating at 600 GHz. 2011-04-01T04:40:41.325Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12341 We study decoherence of the external degree of freedom of a tracer particle moving in a one dimensional dilute Boltzmann gas. We find that phase averaging is the dominant decoherence effect, rather than information exchange between tracer and gas particles. While a coherent superposition of two wave packets with different mean positions quickly turns into a mixed state, it is demonstrated that such superpositions of different momenta are robust to phase averaging, until the two wave packets acquire a different position due to the different velocity of each wave packet. 2011-03-28T16:00:07.123Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12318 WS-BPEL is for specifying business process behaviour based on Web services. Business processes can be very long and encounter expected or unexpected exceptions. Compensations, or dealing with faults, can be a long, complex and imperfect process. In this paper, the FCT-Handlers of WS-BPEL are analysed to show the features that might be modified to be suitable for the real business processes in 3rd party logistics applications. 2011-03-24T22:00:11.966Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12317 In lossless periodic media, the concept of group velocity is fundamental to the study of propagation dynamics. When spatially averaged, the group velocity is numerically equivalent to energy velocity, defined as the ratio of energy flux to energy density of modal fields. However, in lossy media, energy velocity diverges from group velocity. Here, we define a modal field velocity which remains equal to the complex modal group velocity in homogeneous and periodic media. The definition extends to the more general situation of modal fields that exhibit spatial or temporal decay due to lossy elements or Bragg reflection effects. Our simple expression relies on a generalization of the concepts of energy flux and density. Numerical examples, such as a two-dimensional square array of silver rods in vacuum, are provided to confirm the result. Examples demonstrate how the dispersion relation of the periodic structure, the properties of its modes, and their group velocities change markedly in lossy media. 2011-03-24T13:20:14.463Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12298 A simplified, cost-effective millimeter-wave radio-over-fiber system is proposed by heterodyning two independent low-cost light-sources and RF homodyning at the receiver that suppresses phase-noise effects. Proposed system avoids phase/frequency locking, high-speed modulators and local oscillators/mixers in CO and BSs. 2011-03-23T08:20:25.127Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12284 22 page(s) 2011-03-23T02:00:25.833Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12288 In this paper, a solid-state UV Raman laser pumped at by a Q-switched 532 nm laser that utilizes intracavity sum-frequency mixing to generate more than 20 wavelengths in range 266-321nm, is reported. The Raman laser consisted of a KGd(WO4)2 Raman crystal and beta-barium borate (BBO) crystal positioned in a resonator. The input coupler is highly transmissive at 532 nm and highly reflective for the first three Stokes orders. The second harmonic or sum frequencies of the intracavity Stokes and fundamental fields were coupled from the resonator using a UV reflecting dichroic mirror placed between the BBO crystal and the Raman crystal. We conclude that the intracavity Raman laser provides a wavelength versatile source of UV at wavelengths spanning and neighbouring the UV-B (285-315nm). 2011-03-23T02:00:20.630Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12051 Fibre Bragg gratings inscribed with the point-by-point method using a Ti-sapphire femtosecond laser operating at 800 nm are shown to display strong increasing attenuation towards shorter wavelengths with a large and spectrally sharp recovery observed below 400 nm. The origin of this loss is shown to be Mie scattering, and the sharp recovery in the transmission results from wavelength dependent scattering within the numerical aperture of the core. The permanent losses from these Type II gratings have implications for high temperature sensors and fibre lasers. 2011-03-03T08:20:56.439Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12052 A femtosecond laser with a 1 kHz repetition rate and two different polarization states was used to fabricate low-loss waveguides in fused silica. Investigations of chemically-mechanically polished waveguide regions using near-field scanning optical microscopy revealed the presence of modifications outside the glass regions directly exposed to a circularly polarized writing laser. These waveguides also exhibited refractive index contrast up to twice as large as that of waveguides written with linearly polarized radiation. The observed differences in refractive index were shown by Raman spectroscopy to correlate to an increased concentration of 3-member silicon-oxygen ring structures. We propose that the observed differences in material properties are due to the polarization dependence of photo-ionization rates in fused silica. 2011-03-03T08:20:41.842Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12053 We report the fabrication and performance of the first C-band directly written monolithic waveguide laser (WGL). The WGL device was created in an erbium- and ytterbium-doped phosphate glass host and consisted of an optical waveguide that included a distributed feedback Bragg grating structure. The femtosecond laser direct-write technique was used to create both the waveguide and the waveguide-Bragg grating simultaneously and in a single processing step. The waveguide laser was optically pumped at approximately 980 nm and lased at 1537 nm with a bandwidth of less than 4 pm. 2011-03-03T08:20:37.909Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12048 A femtosecond-laser-written monolithic waveguide laser (WGL) oscillator based on a distributed-feedback architecture and fabricated in ytterbium-doped phosphate glass is reported. The device lased at 1033 nm with an output power of 102 mW and a bandwidth of less than 2 pm when bidirectionally pumped at 976 nm. The WGL device was stable and operated for 50 h without degradation. This demonstration of a high-performance WGL opens the possibility for creating a variety of narrow-linewidth laser designs in bulk glasses. 2011-03-03T02:50:49.620Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12047 We report photonic quantum circuits created using an ultrafast laser processing technique that is rapid, requires no lithographic mask and can be used to create three-dimensional networks of waveguide devices. We have characterized directional couplers—the key functional elements of photonic quantum circuits—and found that they perform as well as lithographically produced waveguide devices. We further demonstrate high-performance interferometers and an important multi-photon quantum interference phenomenon for the first time in integrated optics. This direct-write approach will enable the rapid development of sophisticated quantum optical circuits and their scaling into three-dimensions. 2011-03-03T02:50:43.990Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12050 Fiber Bragg gratings inscribed with a femtosecond laser using the point-by-point (PbP) technique have polarization dependent grating strength (PDGS) and exhibit birefringence. In this paper we quantify the dependence of these two properties on the ellipticity, position in the core and size of the micro-voids at the center of each refractive index modulation. We demonstrate that the effective modal index for type II gratings written with a femtosecond laser using the PbP method must be lower than that of the pristine fiber, and for the first time associate an axis with a polarization such that the long axis of the elliptically-shaped index modulations corresponds to the slow axis of the gratings. We exploit the PDGS of two gratings used as frequency-selective feedback elements as well as appropriate coiling, to realize a linearly-polarized fiber laser with a low birefringence fiber cavity. We show that the polarization-dependent grating strength is a function of the writing pulse energy and that only gratings optimized for this property will linearly polarize the fiber laser. The fiber lasers have high extinction ratios (>30 dB) for fiber lengths of up to 10 m and very stable polarized output powers (<0.5% amplitude fluctuations) in the range of 20-65 mW at 1540 nm. This method of polarization discrimination allows the realization of highly robust and simplified linearly polarized fiber lasers. 2011-03-03T02:50:14.260Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12015 We study the relaxation oscillations in a continuous-wave intracavity Raman laser both theoretically and experimentally. Analytic expressions for the relaxation oscillation frequency are derived from the rate-equations and are validated by experiments. We show that some important experimental parameters such as the effective Raman gain coefficient and intracavity Stokes loss can be determined simply by measuring the relaxation oscillation frequency versus pump power. 2011-03-02T07:11:54.012Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12019 We report the generation of 5.3 W cw laser emission at 559 nm by sum-frequency mixing of the fundamental and first-Stokes fields generated within an Nd:GdVO₄ self-Raman laser. A high overall diode-to-visible conversion efficiency of 21% is demonstrated. We discuss the balance that must be maintained between the two nonlinear processes of Raman generation and sum-frequency mixing in order to obtain maximum emission at 559 nm. 2011-03-02T07:11:39.269Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12021 We report a continuous-wave Nd:GdVO₄ self-Raman laser generating wavelength-selectable output in the green-yellow spectral region. The laser combines stimulated Raman scattering (SRS) with intracavity second harmonic and sum-frequency generation (SHG/SFG) to enable “on-demand” operation at any one of three wavelengths, 532 nm, 559 nm and 586 nm, each with output power greater than 3.5 W. Using experimental and numerical modelling results, we show how the highly-interactive, simultaneous non-linear processes of SRS and SHG/SFG may be balanced to achieve stable, selectable multi-wavelength visible operation. 2011-03-02T07:11:26.812Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12001 All-fiber lasers offer increased robustness and simplicity over other fiber laser systems. Current active Q-switching techniques for all-fiber lasers rely on electro-mechanical transducers to strain-tune an intra-cavity fiber-Bragg grating, which adds complexity and can lead to vibrational sensitivity. An all-optical technique for achieving active Q-switched operation is a more elegant approach and would maintain the inherent robustness and simplicity of an all-fiber laser system. In this work, we studied the optical tuning of a fiber-Bragg grating by resonant optical pumping and optimized it for application to active systems. We incorporated an optically-tunable fiber-Bragg grating into a fiber laser and demonstrated active Q-switching at 35 kHz with this all-optical, all-fiber laser system. We highlight the potential to operate at >300 kHz with the current embodiment. To our knowledge, this is the first demonstration of an optically-driven active Q-switch in a fiber laser. Further potential to operate at MHz frequencies is discussed. 2011-03-01T04:30:49.632Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12002 We study the optical properties of a two-axis galvanometric optical scanner constituted by a pair of rotating planar mirrors, focusing our attention on the transformation induced on the polarization state of the input beam. We obtain the matrix that defines the transformation of the propagation direction of the beam and the Jones matrix that defines the transformation of the polarization state. Both matrices are expressed in terms of the rotation angles of two mirrors. Finally, we calculate the parameters of the general rotation in the Poincaré sphere that describes the change in the polarization state for each mutual orientation of the mirrors. 2011-03-01T04:30:41.614Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11120 In this paper we analyze some important characteristics of the spatial Wigner function of entangled photon pairs. We show that the Wigner description of quantum states that live in the infinite-dimensional space-momentum degree of freedom proves to be particularly useful. We propose an experimental configuration that can be used to retrieve the Wigner function of paired photons entangled in the spatial degree of freedom. In particular, it allows the full characterization of the paired photons emitted from a spontaneous parametric down-conversion source. 2011-02-18T15:30:40.227Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11880 To model the light-guiding properties of a hexagonal array of dielectric cylinders, we have numerically solved Maxwell's equations with the finite-difference time-domain technique. The sizes and refractive indices of the cylinders are representative of those of the outer segments of the cone photoreceptors in the human central retina. In the array, light propagates predominantly as a “slow” mode, with a noticeable contribution of a “fast” mode, with the optical field localized in the intra- and inter-cylinder spaces, respectively. Interference between these modes leads to substantial (up to approximately 60%) axial oscillations in optical power within the cylinders. Our numerical model offered approximate dependence of the optical intensity distribution within the cylinders on their radii and separations. 2011-02-18T15:30:28.714Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11879 An external-cavity diamond Raman laser generating up to 2.0 W at 1240 nm from 3: 3 W of 1064 nm pump power is investigated as a function of pump polarization direction. The maximum conversion efficiency was 61%, and the slope efficiency of 84% closely approaches the quantum limit of 85.8%. The lowest threshold for Raman lasing is achieved for pump polarization parallel to the < 111 > axis, which we show is consistent with theory. 2011-02-18T15:30:27.879Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11881 We describe and experimentally demonstrate a novel (to our knowledge) surface profiling technique, for which we propose the term closed-loop optical coherence topography. This technique is a scanning beam, servo-locked variation of low-coherence interferometry. It allows for the sub-wavelength-resolution tracking of a weakly scattering macroscopic-scale surface, with the surface profile being directly output by the controlling electronics. The absence of significant real-time computational overhead makes the technique well suited to high-speed tracking. The use of a micrometer-scale coherence gate efficiently suppresses signals arising from structures not associated with the surface. These features make the technique particularly well suited to real-time surface profiling of in vivo, macroscopic biological surfaces, 2011-02-18T15:30:14.482Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11870 We report the generation of microwave signals by mixing a tunable semiconductor laser with a short-cavity dualwavelength distributed Bragg reflector (DBR) fiber laser. The DBR laser generated two continuous-wave longitudinal modes separated by 25GHz. 2011-02-17T10:40:30.463Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11869 Microstructured polymer optical fibre was fabricated in which bubbles were randomly distributed in the fibre cladding. The bubbles partly guided and partly scattered light propagating in the fibre core. 2011-02-17T10:40:19.661Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11674 A 10-kHz pulse-repetition-frequency dye-laser master-oscillator power amplifier, end-pumped by a copper vapour laser (CVL), is reported. This laser was based on recently available, lightweight and compact CVL and dye laser components. Dye laser tunability was achieved from 592 to 622 nm and, when the oscillator was etalon line-narrowed, up to 1.5 W of single-etalon-mode output was obtained from the amplifier at the 608-nm peak tuning wavelength. By frequency doubling this amplified output in a BBO crystal we obtained up to 225 mW of 5-GHz 308-nm output, which is suitable for the performance of tropospheric hydroxyl radical concentration measurements. 2011-02-07T09:50:51.636Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11599 Two-mirror beam shaping of a 94% fill-factor laser diode bar was investigated. We show that optimal output for the purposes of end pumping was achieved by configuring the beam shaper to reformat the single row of 60 emitters into an array containing several emitters in each row. A 15×4 output configuration was used to end pump a Yb:S-FAP laser. A nearly on-axis multipass pumping system was developed to demonstrate how the asymmetry of the beam-shaped pump source can be exploited. 2011-02-03T08:21:42.865Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11601 We report a parametric anti-Stokes Raman laser using potassium gadolinium tungstate, generating output chiefly at the first anti-Stokes at 508 nm. The compact 4.5 cm long device is pumped by a Q-switched 532 nm laser and uses an off-axis Stokes resonator to provide non-collinear phase matching between the pump and the generated Stokes and anti-Stokes fields. Anti-Stokes output energies up 0.27 mJ were obtained at a conversion efficiency from the pump of 0.46%. Second- and third-order anti-Stokes lines at 486 nm and 465 nm were also observed. 2011-02-03T08:21:14.992Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11602 We have developed a technique for the temporal characterisation of weak deep-ultraviolet (DUV) ultrashort laser pulses by combining asynchronous optical sampling with difference-frequency mixing. The intensity profile of picosecond DUV pulses, with peak powers as low as 2.5 W, have been measured accurately with a resolution of 50 fs. The method can be extended to complete amplitude and phase characterisation of few femtosecond laser pulses at DUV wavelengths. 2011-02-03T08:21:03.354Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11603 We report mode-locked operation of a synchronously pumped Ce:LiCAF oscillator. The laser operated in the deep UV with output radiation centered at 291 nm and a pulse duration of 6 ps. The maximum output power measured was 52 mW, with 13% slope efficiency. The Ce:LiCAF crystal has a gain bandwidth capable of supporting few-femtosecond pulses, and so our results demonstrate the potential to form a new class of ultrafast lasers operating directly at deep UV wavelengths. 2011-02-03T08:20:54.468Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11604 A novel method is presented for determining the volume of molten material ejected from a substrate as a result of visible pulsed-laser ablation. A 100-μm-wide pulsed-laser light sheet (τ ~ 5 ns, λ = 532 nm) was used in conjunction with a CCD camera to provide high-speed cross-sectional images of single-pulse ablation of aluminum with a visible nanosecond laser source. Computational analysis of the two-dimensional gray-scale images was used to determine the total volume of material ejected from the substrate in the form of molten droplets. Ablation with dual-wavelength (511- and 578-nm) pulses of 30-ns duration was characterized under various fluence conditions (0–25 J cm⁻²), allowing a quantitative threshold for explosive melt ejection in aluminum to be established at ~10 J cm⁻². The temporal evolution of the ejected material showed that, for an incident fluence of ~40 J cm⁻², molten-droplet ejection commenced at ~400 ns and ceased after ~2 μs. 2011-02-03T08:20:39.920Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11440 Picosecond pulse generation by active mode locking and subsequent regenerative amplification in a Nd:vanadate laser crystal has been realized in one and the same cavity using the all-in-one laser concept. An active prelasing stabilization loop has been implemented acting on the mode locker, allowing stable operation up to repetition rates as high as 3 kHz. Sub-30-ps pulses with an energy of 800 μJ have been achieved, constituting the highest peak power and the highest average output power ever demonstrated by means of the all-in-one approach. The combination of compact design, high peak and average power along with a near-diffraction-limited beam profile makes this source a promising tool for precision micromachining applications. 2011-01-22T04:30:13.977Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11439 We experimentally and numerically investigate femtosecond pulse propagation in a microstructured optical fiber consisting of a silica core surrounded by air holes which are filled with a high index fluid. Such fibers have discrete transmission bands which exhibit strong dispersion arising from the scattering resonances of the high index cylinders. We focus on nonlinear propagation near the zero dispersion point of one of these transmission bands. As expected from theory, we observe propagation of a red-shifted soliton which radiates dispersive waves. Using frequency resolved optical gating, we measure the pulse evolution in the time and frequency domains as a function of both fiber length and input power. Experimental data are compared with numerical simulations. 2011-01-22T04:30:04.568Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11365 We describe a dual-core microstructured optical fiber designed for refractive index sensing of fluids. We show that by using the exponential dependence of intercore coupling on analyte refractive index, both large range and high sensitivity can be achieved in the one device. We also show that selective filling of the microstructure with analyte can increase the device sensitivity by approximately 1 order of magnitude. 2011-01-19T04:30:28.564Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11366 We present a fiber laser with a switchable state of linearly polarized output realized by inscribing point-by-point fiber Bragg gratings directly into the active core of a polarization-maintaining fiber. The compact all-fiber system exhibited a very narrow laser linewidth of ~13.5 pm (3.5 GHz), at a maximum continuous-wave output power of 188 mW. The optical signal-to-noise ratio was greater then 62 dB for both lasing polarizations. The robust system exhibited excellent long-term wavelength and laser linewidth stability. 2011-01-19T04:30:17.099Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:11367 We report the demonstration of compact fluidic fibre lasers based on capillary tubes and photonic crystal fibres, featuring single channel and multiple laterally integrated fluidic lasers respectively. Their preparation was based on capillary action and lasing occurred without the need for external mirrors or lithographically defined microstructures. The fibre lasers were found to be tunable by varying the chromophore density in the liquid core and a functional wavelength selectivity mechanism inherent in both types of lasers provided a long free spectral range that does not correspond to the length of the fibres. The enhanced mode spacing is attributed to a Vernier resonant effect. 2011-01-19T04:30:15.582Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:9300 The diffractive properties of gold films with a periodic lattice of sub-micron voids beneath the surface are investigated. It has been shown that nanoporous metal surfaces exhibit frequency-selective non-dispersive diffraction enhanced by Mie plasmons in nanovoids, which leads to absolute angular tolerance of the diffracted beam intensity that can be useful for a variety of applications covering angle-tolerant optical filters, deflectors, absorbers, and beam splitters. Diffraction spectra are measured and calculated to support these conclusions, showing good qualitative agreement. 2011-01-18T01:21:30.702Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:9301 We study the optical plasmonic properties of metal surfaces which have a periodic lattice of voids buried immediately beneath their flat upper surface. Light reflection spectra calculated in the framework of a self-consistent electromagnetic multiple-scattering layer-KKR approach exhibit two types of plasmon resonances originating from the excitation of different plasmon modes: surface plasmon-polaritons propagating on the planar surface of metal and Mie plasmons localized in the buried voids. Coupling between these two types of plasma oscillation leads to an enhancement of the surface plasmon-polariton resonances even for close-packed void lattices. Our theoretical model quantitatively agrees with experimental results, demonstrating that planar surfaces can exhibit strong plasmonic field enhancements. 2011-01-18T01:21:30.507Z ]]>