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High-harmonic generation (HHG), where a short-pulse high-power laser ionises a gas which upon recombination emits high energy radiation, is an exciting option for table-top sources of coherent X-rays and XUV light for imaging and spectroscopy. Traditionally, the pump lasers have been femtosecond Ti:Sapphire lasers. As more high-power ultrafast pump laser systems are becoming commercially available, for example fibre lasers and wavelength shifted systems based on OPAs, it is important to understand how their different operating regimes (wavelength, pulse length, peak power, repetition rate) affect HHG efficiency and flux.

The ability to image matter on the microscopic scale is of fundamental importance to many areas of research and development including pharmacology, materials science and nanotechnology. Owing to its generality, x-ray scattering is one of the most powerful tools available for structural studies. The major limitation however is the necessity of producing suitable crystalline structures – this technique relies upon many x-ray photons being scattered from a large number of molecules with identical orientations. As it is neither possible nor desirable to crystallise every molecule of interest, this has provided a huge drawback for most biotechnologies. Although improvements in both sources and detectors have had a strong impact in this area, driving down the required sample size, the need for macroscopic crystalline samples remains a fundamental bottleneck. Fortunately recent technological developments in the generation and sub-micron focusing of soft x-rays (SXRs) have provided a route for bypassing the need for a regular, crystalline structure. For the purposes of this chapter, SXRs are defined as electromagnetic radiation with wavelengths from 1 – 50 nm, which correspond to photon energies of 1.2 keV – 25 eV respectively. As their wavelengths are on a comparable scale to objects such as proteins, cells and quantum dots, SXRs are ideally suited for imaging these targets with a high spatial resolution. Furthermore water is transparent and carbon opaque to SXRs whose wavelengths lie between 2 – 4 nm, the so-called water window. This offers clear potential for the imaging of biological molecules within their native, aqueous environment, something that would be impossible using traditional x-ray crystallography experiments. Unsurprisingly there has been great interest in the production and application of SXRs across a wide range of scientific endeavours including, but not limited to, resolving electron motion (Drescher et al

This work quantifies water contamination in jet fuel (Jet A-1), using silica-based Bragg gratings. The optical sensor geometry exposes the evanescent optical field of a guided mode to enable refractometery. Quantitative analysis is made in addition to the observation of spectral features consistent with the emulsification of water droplets and Stokes’ settling. The measurements are observed for cooling and heating cycles between ranges of 22 °C and −60 °C. The maximum spectral sensitivity for water contamination was 2.4 pm/ppm-v, with a resolution of

In today's world of advancing technology, pervasive and ubiquitous systems have become more common, and have been adapted for many different areas of use. The Internet-of-Things (IoT) movement has increased in popularity, and there are now many affordable, customizable smart devices available for various purposes. These devices are commonly found in the home, but have yet to infiltrate the scientific laboratory in the same way. Some laboratories do use IoT devices to control and monitor equipment, but smart laboratories just do not exist in the same way as smart homes, until now. This article introduces the use cases for a smart integrated laboratory, and describes a prototype system, Talk2Lab, that was implemented in an experimental laser facility. Talk2Lab uses a combination of sensors, Raspberry Pis, camera feeds, and multiple interaction methods (voice, text, and visual dashboards) to facilitate laboratory communication. It was evaluated by the laboratory users for usability, and to identify potential areas of expansion. The work to date illustrates the type of systems that can be created using IoT devices. From the results of the user evaluation, we have conceptualized a future vision for Talk2Lab: a fully interconnected laboratory of the future.

Imaging using coherent extreme ultraviolet radiation from laser sources provides high-resolution images of biological samples., Microscopy with extreme ultraviolet (EUV) light can provide many advantages over optical, hard x-ray or electron-based techniques. However, traditional EUV sources and optics have large disadvantages of scale and cost. Here, we demonstrate the use of a laboratory-scale, coherent EUV source to image biological samples—mouse hippocampal neurons—providing quantitative phase and amplitude transmission information with a lateral resolution of 80 nm and an axial sensitivity of ~1 nm. A comparison with fluorescence imaging of the same samples demonstrated EUV imaging was able to identify, without the need for staining or superresolution techniques

The impact of femtosecond lasers across science and engineering has been significant. The one area which has so far proved hard to access for femtosecond lasers has been the combination of high peak power and high average power. This review seeks to highlight the issues which make high average power hard to achieve in many femtosecond systems, and looks at the routes that are now being taken to achieve the goal of high peak and high average power.

Chemical scientists’ experiences with LabTrove., Electronic Laboratory Notebooks (ELNs) are progressively replacing traditional paper books in both commercial research establishments and academic institutions. University researchers require specific features from ELNs, given the need to promote cross-institutional collaborative working, to enable the sharing of procedures and results, and to facilitate publication. The LabTrove ELN, which we use as our exemplar, was designed to be researcher-centric (i.e., not only aimed at the individual researcher's basic needs rather than to a specific institutional or subject or disciplinary agenda, but also able to be tailored because it is open source). LabTrove is being used in a heterogeneous set of academic laboratories, for a range of purposes, including analytical chemistry, X-ray studies, drug discovery and a biomaterials project. Researchers use the ELN for recording experiments, preserving data collected, and for project coordination. This perspective article describes the experiences of those researchers from several viewpoints, demonstrating how a web-based open source electronic notebook can meet the diverse needs of academic researchers.

The development of an Yb3+-fiber based chirped-pulse amplification system and the performance in the generation of extreme ultraviolet (EUV) radiation by high-harmonic generation is reported. The fiber laser produced 100 µJ, 350 fs output pulses with diffraction limited beam quality at a repetition rate of 16.7 kHz. The system used commercial single-mode, polarization maintaining fiber technology. This included a 40 µm core, easily packaged, bendable final amplifier fiber in order to enable a compact system, to reduce cost, and provide reliable and environmentally stable long term performance. The system enabled the generation of 0.4 µW of EUV at wavelengths between 27-80 nm with a peak at ~45 nm using xenon gas. The EUV flux of ~1011 photons per second for a driving field power of 1.67 W represents state-of-the-art generation efficiency for single-fiber amplifier CPA systems, corresponding to a maximum calculated energy conversion efficiency of 2.4 x 10-7 from the infra-red to the EUV. The potential for high average power operation at increased repetition rates and further suggested technical improvements are discussed. Future applications could include coherent diffractive imaging in the EUV, and high-harmonic spectroscopy.

The growing interest in the study of the extreme ultraviolet (EUV) radiation-matter interaction is feeding up the development of new technologies able to overcame some current technological limits. Adaptive optics is an established technology already widely used for wavefront correction in many applications such as astronomical telescopes, laser communications, high power laser systems, microscopy and high resolution imaging systems. Although this technology is already exploited in the EUV and X-ray range, its usage is only feasible in systems with a grazing incidence configuration. On the other hand, the development of a EUV normal incidence adaptive optics can open new interesting possibilities in many different fields ranging from free electron laser and synchrotron applications up to EUV photolithography. In this work we report the preliminary results achieved in the developing of a normal incidence EUV multilayered adaptive mirror tuned at 30.4nm. The proper functioning and potential applications of such device have been demonstrated by using a High order Harmonics Generation (HHG) source.

The design and fabrication of nanopores within three-dimensionally structured gold films with spherical microcavities of 1.2 µm diameter and 0.6 µm deep in hexagonal close-packed arrays, are described. The cavities are fabricated by electroplating gold around self-assembled arrays of polymer spheres. Following removal of the spheres, and 'lift-off' of the 3D structured gold film, some of the microcavities were milled with a Helium Ion Microscope to provide nanopores through the centre of the microcavity base right through the film. The geometry of the nanopore within the device is designed using theoretical approaches to provide the optimal electric field intensity in the very centre of the nanopore when excited with light of ~ 600 nm (in water). In this paper we report the theoretical simulations used to evaluate the optimal geometry of the nanopore within the centre/base of the gold microcavity. Although a number of various geometries and sizes of pores were considered the theoretical results provide evidence that a pore of 50nm with rounded corners will provide the greatest electrical field intensity inside the pore and the fabrication results provide a demonstrated practical approach for creation of these nanopores within these 3D gold structured films.

Journal of the Optical Society of Korea : JOSK 20(2), 245-250 (2016). doi:10.3807/JOSK.2016.20.2.245, Published by OSK, Soul

Applied physics express 9(7), 076701 (2016). doi:10.7567/APEX.9.076701, Published by ¯Oy¯o Butsuri-Gakkai, Tokyo

We present coherent diffractive imaging with broadband radiation generated from a high harmonic source around 29nm wavelength to image neuron tissue from the mouse hypothalamus to 80nm resolution over a 40nm field of view.

Three-dimensionally structured gold membrane films with nanopores of defined, periodic geometries are designed and fabricated to provide the spatially localised enhancement of electric fields by manipulation of the plasmons inside nanopores. Square nanopores of different size and orientation relative to the pyramid are considered for films in aqueous and air environments, which allow for control of the position of electric fields within the structure. Designs suitable for use with 780 nm light were created. Here, periodic pyramidal cavities produced by potassium hydroxide etching to the {111} planes of (100) silicon substrates are used as templates for creating a periodic, pyramidal structured, free-standing thin gold film. Consistent with the findings from the theoretical studies, a nano-sized hole of 50 nm square was milled through the gold film at a specific location in the cavity to provide electric field control which can subsequently used for enhancement of fluorescence or Raman scattering of molecules in the nanopore.

We report the demonstration of a scanning probe coherent diffractive imaging method (also known as ptychographic CDI) using a compact and partially coherent gas-discharge plasma source of extreme ultraviolet (EUV) radiation at a 17.3 nm wavelength. Until now, CDI has been mainly carried out with coherent, high-brightness light sources, such as third generation synchrotrons, x-ray free-electron lasers, and high harmonic generation. Here we performed ptychographic lensless imaging of an extended sample using a compact, lab-scale source. The CDI reconstructions were achieved by applying constraint relaxation to the CDI algorithm. Experimental results indicate that our method can handle the low spatial coherence and broadband nature of the EUV illumination, as well as the residual background due to visible light emitted by the gas-discharge source. The ability to conduct ptychographic imaging with lab-scale and partially coherent EUV sources is expected to significantly expand the applications of this powerful CDI method.

High-harmonic generation (HHG) offers better coherence1, shorter pulse durations2 and far greater accessibility than synchrotron sources3. These factors make HHG an increasingly important source of soft X-rays and an excellent resource in many emerging areas, for example, the time-resolved study of conformational changes in single biological molecules4. Here, we demonstrate a novel technique that enables us to reconstruct spectral information spatially across an X-ray beam. As only a single diffraction image is required per measurement, this technique is well suited to time-resolved studies. This technique is applicable to many types of X-ray source3,5,6,7 and can be adapted for different spectral regions. Here, results are obtained using a capillary high-harmonic source8, revealing detailed information that brings new insight into the physical processes occurring inside the source and enabling us to show the first measurement of radial variation of harmonic order in the emission from an HHG capillary.

Coherent diffractive imaging (CDI) and related techniques enable a new type of diffraction-limited high-resolution extreme ultraviolet (EUV) microscopy. Here, we demonstrate CDI reconstruction of a complex valued object under illumination by a compact gas-discharge EUV light source emitting at 17.3 nm (O VI spectral line). The image reconstruction method accounts for the partial spatial coherence of the radiation and allows imaging even with residual background light. These results are a first step towards laboratory-scale CDI with a gas-discharge light source for applications including mask inspection for EUV lithography, metrology and astronomy.

Coherent diffractive imaging (CDI) and related techniques enable a new type of diffraction-limited high resolution microscopy and have been widely used in the extreme ultraviolet (EUV) and X-ray communities. In this experiment, we demonstrate CDI using a compact gas-discharge EUV light source with a wavelength of 17.3 nm (oxygen VI emission). Our image reconstruction method accounts for the partial spatial coherence of the radiation using a deconvolution technique. Our results are promising for future laboratory-scale CDI applications, including mask inspection for EUV lithography and EUV metrology.

The possibilities and limitations of proximity and interference lithography under extreme ultraviolet (EUV) radiation are explored. Utilizing partially coherent EUV radiation at central wavelength of 10.9 nm from a Xe gas discharge plasma source, it is shown that proximity printing in the Fresnel diffraction regime can produce the high-resolution features even with low-resolution masks, and also yield sub-30 nm edge resolution in the resist. The scalability limit within non-paraxial case has been also studied. The effect of the diffraction behind the transmission mask is evaluated with respect to the achievable resolution. The finite-difference time-domain simulation of the diffraction patterns behind the Ni/Nb-based transmission mask is performed varying the pitch size. The results demonstrate that the method can be used to produce patterns with resolution down to 7.5 nm half-pitch with 2:1 mask demagnification utilizing achromatic Talbot effect with transverse electric (TE)-polarized light.

With the aim of improving imaging using table-top extreme ultraviolet sources, we demonstrate coherent diffraction imaging (CDI) with relative bandwidth of 20%. The coherence properties of the illumination probe are identified using the same imaging setup. The presented methods allows for the use of fewer monochromating optics, obtaining higher flux at the sample and thus reach higher resolution or shorter exposure time. This is important in the case of ptychography when a large number of diffraction patterns need to be collected. Our microscopy setup was tested on a reconstruction of an extended sample to show the quality of the reconstruction. We show that high harmonic generation based EUV tabletop microscope can provide reconstruction of samples with a large field of view and high resolution without additional prior knowledge about the sample or illumination

Fractional Talbot effect leads to the possibility to implement patterning of structures with smaller periods than the master mask. This is particularly attractive when using short wavelength illumination in the extreme ultraviolet because of attainable resolution in the sub-100-nm range. In this Letter, we demonstrate the Talbot lithography with the fractional Talbot effect under coherent illumination generated with a capillary discharge Ne-like Ar extreme ultraviolet laser. Various spatial frequency multiplications up to 5x are achieved using a parent grating. This technique allows a fabrication of nanostructures with high-resolution patterns, which is of high interest in many applications such as the manufacturing of plasmonic surfaces and photonic devices.

pH sensors were developed by covalently attaching para-Methyl Red and (4-carboxyphenyl)-Bromophenol Blue onto macroporous glass beads. The beads were integrated into a readily fabricated sensor assembly coupled to a fibre optic spectrometer. The sensor was shown to be durable and had a rapid response time compared to other fibre optic sensor devices and electrochemical pH meters.

Transparent oxyfluoride glass-ceramic materials are of significant interest for the production of new optoelectronic devices. In this paper we report measurements of the detailed spectroscopy of rare earth dopants in both an oxyfluoride transparent glass ceramic and its glass precursor. We show that several spectroscopically different sites exist for the rare earth even in the glass precursor material, where a significant amount of the rare earth is already coordinated with fluorine. In the glass-ceramic material, these glassy fluorine-coordinated sites are replaced with crystalline sites, but a significant fraction of the rare earth ions are still within the glass phase. The fraction of rare earth ion that is incorporated into the crystalline phase is estimated from the rare earth spectroscopy, and the role of the rare earth coordination in the precursor glass is discussed.

Fluorescence microscopy is a powerful technique for analyzing beads with very low loadings of fluorophores; however, the method is flawed when looking at more highly loaded beads as a result of severe problems with absorption. To probe distributions at higher loading levels, Raman spectroscopy avoids many of these issues. These studies show that there is a uniform distribution of reactive sites throughout the beads but that the spatial distribution of reacted sites depends on the polymer type, with a fine balance between reaction and diffusion rate.

Coherent diffractive imaging (CDI) has become a standard method on a variety of synchrotron beam lines. The high brilliance short wavelength radiation from these sources can be used to reconstruct attenuation and relative phase of a sample with nanometre resolution via CDI methods. However, the interaction between the sample and high energy ionising radiation can cause degradation to sample structure. We demonstrate, using a laboratory based high harmonic generation (HHG) based extreme ultraviolet (EUV) source, imaging a sample of hippocampal neurons using the ptychography method. The significant increase in contrast of the sample in the EUV light allows identification of damage induced from exposure to 7.3 keV photons, without causing any damage to the sample itself.Report of talk given at 13th International X-Ray Microscopy Conference (XRM), Diamond Light Source, Oxford, UK, 15-19 Aug 2017

Detection of DNA sequences is pivotal to many modern molecular diagnostic methods, but the ability to directly detect DNA sequences, without the need for signal amplification (such as by applying a polymerase chain reactions) is highly desirable. Here we investigate the potential for gold inverted pyramidal structures (also known as Klarite®) for DNA detection, as these simple chips containing the structured surface on a face could offer an improved format for DNA based diagnostic methods. Our strategy included optimization of the fabrication protocols to achieve flat gold surfaces within the inverted pyramidal surface and then a subsequent assessment of these substrates for direct DNA detection by Raman microscopy. These studies demonstrate for the first time the potential of these gold structured planar substrates for DNA analysis applications.

The application of petawatt lasers to scientific and technological problems is advancing rapidly. The usefulness of these applications will depend on being able to produce petawatt pulses at much higher repetition rates than is presently possible. The International Coherent Amplification Network (ICAN) consortium seeks to design high repetition rate petawatt lasers using large scale coherent beam combination of femtosecond pulse amplifiers built from optical fibres. This combination of technologies has the potential to overcome many of the hurdles to high energy, high average power pulsed lasers, opening up applications and meeting societal challenges.

We examine the spatiotemporal compression of energetic femtosecond laser pulses within short gas-filled fibers. The study is undertaken using an advanced nonlinear pulse propagation model based on a multimode generalized nonlinear Schrödinger equation that has been modified to include plasma effects. Plasma defocusing and linear propagation effects are shown to be the dominant processes within a highly dynamical mechanism that enables 100-fs pulses to be compressed into the few-cycle regime after

We present a novel technique for estimating the radius of curvature from a single exposure of EUV light from a high harmonic source diffracted by a grating of square apertures.

We report the experimental measurements for etch rates of the +z and -z faces of single crystal lithium niobate immersed in HF and HNO3 acid mixtures of varying ratios. We find that pure HF produces an etch rate that is a factor of 2 higher than the rate obtained for the more frequently used mixture of HF/HNO3 in a 1 : 2 ratio. We further observe that the quality of etching is improved for either pure HF or HF/HNO3 in a 1 : 4 ratio, again by comparison with use of a 1 : 2 ratio. These results lead to a discussion of the etch chemistry involved, and an explanation for the observed high degree of differential etching between the +z and -z crystal faces.

Scanning confocal Raman spectroscopy was used to study the distribution of reactive sites within a resin bead used for solid-phase synthesis. The distribution of NH2 groups in aminomethylated polystyrene resin (APS) was determined by doping with varying amounts of 4-cyanobenzoic acid. The extent of loading was determined by both elemental analysis and ninhydrin assays. The spatial distribution of the coupled 4-cyanobenzamide within the bead was determined to an in-plane resolution of 1 microm and depth resolution of about 4 microm, using the strong Raman CN stretching vibrational transition at 2230 cm(-1). Dry and swollen beads were studied and the distribution was found to be essentially uniform throughout the bead in all cases.

The production of competitive fibre amplifiers in the 1.3µm region requires both good quantum efficiency in the lasing ion and the capability to produce low-loss fibers. Alkali metal halide substituted gallium lanthanum sulphide (GLS) doped with Pr3+ may provide a route to both. We describe measurements of the optical spectroscopy and radiative quantum efficiency (RQE) of Pr3+ emission at 1.3µm from the 1G4 - 3H5 transition in GLS glass containing CsCl, CsI and RbCl. The results indicate that CsCl-containing GLS glasses. which have better thermal and glass-forming properties than pure GLS, can show quantum efficiencies of up to ~80% of that of pure GLS and thus are good candidates for 1.3µm fiber amplifiers.

The intense few-cycle driving fields used to produce isolated attosecond pulses via high harmonic generation (HHG) [1] are typically delivered from conventional hollow fiber compressors. However, it has been suggested that individual attosecond pulses may be realized in low-pressure regions at the output of self-compressed filaments [2]. We follow a similar approach in an alternative geometry and present modelling of an elegant source of isolated attosecond pulses driven by a 40 fs near infrared (NIR) laser field. Here, ionization-induced self-compression and HHG happen in-situ within a short (40 mm) gas-filled fiber, and single 350 as pulses at a central wavelength of 13.5 nm are predicted at its exit.

This paper presents a novel technique for characterising wavefront curvature and M2, by utilising a non-redundant array (NRA) of apertures to define the plane of investigation through an experimental extreme ultraviolet (EUV) focus. Appropriately sampled, far-field EUV scattering from this NRA is captured on a CCD as the NRA is scanned along the beam axis through the focus. By taking the inverse Fourier transform (IFT), it is possible obtain the spatial autocorrelation functions, via the Wiener-Khinchin theorem, of the exit wave field. By observing the position of the first-order peaks in the autocorrelation as a function of grid translation, both the real and imaginary parts of the complex beam parameter can be determined and the M2 calculated, yielding full characterisation of the embedded Gaussian. Since the periodicity of the grid is known, the planar pixel resolution can be calculated, also allowing the translations movement to be confirmed due to the change in angular acceptance of the fixed CCD. This makes the technique self-calibrating. A high impact, easy to use, cross field technique for full profiling of the embedded Gaussian of probe beams using a non-redundant array of apertures is presented. The technique is experimentally verified in the highly absorbing EUV spectral regime, and is expected to play a significant role in other regimes, where experimental issues prevent the use of existing techniques.

Multimodal nonlinear propagation dominates the evolution of intense laser pulses propagating in high-pressure gas-filled capillaries used for high harmonic generation. A fully multimodal nonlinear propagation model is used to predict pulse evolution along such a capillary, and the length and pressure distribution are optimized to produce the shortest pulses at the capillary output. This optimization is shown theoretically to result in self-compression of the pulse from $\ensuremath{\sim}$53 to $\ensuremath{\sim}$7 fs, and is shown experimentally to increase the flux of high harmonic radiation from the capillary by an order of magnitude over comparable capillary and gas jet designs.

We report on a series of ytterbium - erbium codoped aluminophosphosilicate fibres fabricated by the MCVD and solution doping technique where the concentration of aluminium is gradually increased in the region [Al] < [P]. We observe from deflection measurements that with increasing aluminium content the refractive index decreases and the phase separation increases. Laser slope efficiencies decrease when the aluminium concentration approaches the phosphorus concentration and the trend is seen to be correlated with the reduction in energy transfer rate when the aluminium concentration is increased. Raman spectra show the reduction of the highest phonon energy peak when the aluminium content is increased. The erbium 4 I (13/2) to 4 I (15/2) transition fluorescence spectrum and the lifetime of the erbium 4S(3/2) level show little change from the pure phosphosilicate host for the whole range of aluminium concentrations tested. The results are explained in term of formation of AlPO4 structural units.

Laser illumination of optical fibres can modify the refractive index of germano-silicate fibres and introduce optical non-linearity. New luminescence data not only confirm that the laser treatments are wavelength specific, but also the defect structures are altered. Low temperature thermoluminescence of fibres, previously illuminated at 476 nm, gives a glow peak of

This paper details measurements of 1.0 µm 3H4 to 1G4 absorption and site selective studies of the 1.3µm 1G4 to 3H5 fluorescence of Pr3+-doped gallium lanthanum sulphide (GLS) glasses containing oxide impurities. This oxide produces a second, preferentially-occupied site for the Pr3+ within the GLS, which increases the inhomogeneity of the spectral lines, and decreases the lifetime and the quantum efficiency of the 1G4 level.

A stable and self-starting femtosecond breathing-pulse Yb-fiber oscillator is reported, mode-locked using the non-linear polarization evolution mechanism. A bifurcation between two distinct modes of operation is demonstrated experimentally, producing pulses with a single central wavelength in one state, or following adjustment of the intracavity waveplates, the emission of pulses with three distinct central wavelengths. The maximum bandwidth was 72 nm at the -10 dB level, and the pulses were compressible externally to 70 fs with energies of 0.75 nJ. The multiwavelength pulses reported here are significantly shorter than the picosecond pulses previously observed from similar mode-locked multiwavelength sources. Vector simulations based on the nonlinear Schrodinger equation show that the multiwavelength behavior is produced by overdriving the nonlinear polarization evolution-based saturable absorber at the peak of the pulse, leading to transmission of the two wings of the strongly chirped pulse. This new insight shows clearly that the three pulses output in the multiwavelength state are coherent. The agreement between simulation and experimental data shows nonlinear polarization evolution-based mode-locked fiber lasers are a suitable platform for studying the nonlinear dynamics underlying the bifurcation of the output. (C) 2016 Optical Society of America

The fabrication of a highly efficient Nd3+-doped single-mode fiber laser operating at 1.06km is described. The Nd3+ is introduced by doping Nd2O3 into a multicomponent (flint) lead-silicate glass host, Schott commercial optical glass FV. A fabrication technique for doping rare-earth evenly into commercial optical glasses is demonstrated. Spectroscopic properties relevant to laser operation in the Nd3+-doped lead-silicate glass fibers were measured and the influence of Pb2+ ions on the spectral properties was analyzed. Owing to the long lifetime and large absorption and emission cross-sections of Nd3+ in this lead-silicate glass host, a high-performance Nd3+-doped lead-silicate fibre laser device operating at 1.06µm has been successfully demonstrated.

Resonant excitation Yb3+ at 974 nm (10267 /cm) in codoped Yb3+-Tb3+ silica based fibres has lead to luminescence clearly being visible from the Tb3+ 5D4 level (20661 /cm). Through time resolved fluorescence measurements we have been able to directly assign the process responsible for the fluorescence to cooperative sensitisation of the Tb3+ 5D4 level by two excited Yb3+ ions. Energy transfer times for the cooperative process have been directly measured, enabling the effects of glass structure on the cooperative process to be explored. Numerical simulations based on the experimental findings have been conducted, enabling both the mechanism for the luminescence to be confirmed and the properties associated with the luminescence to be interpreted.

We present a simple phase-matching model that takes into account the full spatiotemporal nature of capillary high-harmonic generation. Spectra predicted from the model are compared to experimental results for a number of gases and are shown to reproduce the spectral envelope of experimentally generated harmonics. The model demonstrates that an ionization-induced phase mismatch is limiting the energy of the generated harmonics in current capillary high-harmonic generation experiments. The success of this model shows that phase-matching processes play a dominant role in determining the emission from capillary high-harmonic generation.

Multimode simulations predict dramatic ionization-induced self-compression of high energy ultrashort pulses within short gas filled capillaries. The mechanism observed allows for the temporal compression of 53 fs pulses into the few-cycle regime.

Coherent anti-Stokes Raman scattering (CARS) microscopy is applied for the first time for the evaluation of the protein secondary structure of polyglutamine (polyQ) aggregates in vivo. Our approach demonstrates the potential for translating information about protein structure that has been obtained in vitro by X-ray diffraction into a microscopy technique that allows the same protein structure to be detected in vivo. For these studies, fibres of polyQ containing peptides (D2Q15K2) were assembled in vitro and examined by electron microscopy and X-ray diffraction methods; the fibril structure was shown to be cross β-sheet. The same polyQ fibres were evaluated by Raman spectroscopy and this further confirmed the β-sheet structure, but indicated that the structure is highly rigid, as indicated by the strong Amide I signal at 1659 cm-1. CARS spectra were simulated using the Raman spectrum taking into account potential non-resonant contributions, providing evidence that the Amide I signal remains strong, but slightly shifted to lower wavenumbers. Combined CARS (1657 cm-1) and multi-photon fluorescence microscopy of chimeric fusions of yellow fluorescent protein (YFP) with polyQ (Q40) expressed in the body wall muscle cells of Caenorhabditis elegans nematodes (1 day old adult hermaphrodites) revealed diffuse and foci patterns of Q40-YFP that were both fluorescent and exhibited stronger CARS (1657 cm-1) signals than in surrounding tissues at the resonance for the cross β-sheet polyQ in vitro.

We describe the properties of tantalum-doped silica fibers which have been doped with thulium and produced by a normal solution doping technique. In silica fibers, non-radiative decay almost quenches luminescence from several of the Tm levels, notably the 3F4 level at 800 nm, and the 1H4 level at 2µm. The properties of these levels are a sensitive test of multiphonon decay rates in the host. We observe fluorescence decay components from these levels in Tm-doped tantalosilicate fibers which are significantly longer than those observed in Tm-doped germanosilicate or aluminosilicate fibers. This is interpreted as the formation of a low-vibrational-energy microenvironment around the rare earth.

The homogeneous line width of the1D2-3H4 electronic transition of Pr3+ in ZBLAN and gallium-lanthanum-sulphide (GLS) glass has been determined at 1.9 K by means of hole burning. In ZBLAN the holes show a variation in burning efficiency dependent on probe wavelength. Site-selective fluorescence results are presented to explain this effect

Evidence is presented that erbium will occupy one of two sites in phospho-aluminosilicate glass dependent on the Al : P ratio. Although high energy P=O vibrational modes are created we suggest these are localised and only couple to one type of Er site. Decay rates and Er-Yb amplifier performance are then critically determined by the Al : P ratio.