Μm Beam Research Articles

Nondestructive Differentiation of Polyester Single White Fibers Using Synchrotron Radiation Microbeam X-ray Fluorescence Spectrometry with Vertical Focusing.

In this study, the nondestructive differentiation of individual white polyester clothing fibers was accomplished via synchrotron radiation microbeam X-ray fluorescence (SR-μ-XRF) analysis. SR-μ-XRF with vertical focusing is a useful nondestructive method for the analysis of a single polyester clothing fiber. Kirkpatrick-Baez (KB) mirror was used to vertically focus 20 keV X-rays for the analysis of 22 individual white polyester fibers taken from clothing commonly sold in Japan. SR-μ-XRF with a vertical focused 2 μm (V) × 300 μm (H) beam was approximately 12.8 times more sensitive than SR-XRF with an unfocused 300 μm (V) × 300 μm (H) beam for the detection of elements in single fibers. The minimum detection limits (MDLs) of the SR-μ-XRF method were 8.15 ppm for Cl and 0.06 ppm for Br. In addition to Ti in TiO2 delustering agents, Zr and Nb impurities in the delustering agents were detected in individual fibers. Sb from a polymerization catalyst and Co from a transesterification catalyst were also detected in individual fibers. Comparing the Ti Kβ /Sb Lα,β and Zr Kα /Nb Kα X-ray intensity ratios was a useful way to distinguish individual clothing fibers, and 98% of the fibers were differentiated when additional trace elements were used as discrimination indicators.

A compact electron source for the dielectric laser accelerator

In this work, we design and demonstrate a compact electron source that combines an integrated silicon nanotip photoemitter with a compact silicon-based electrostatic lens. The lens simultaneously accelerates electrons to 30 keV and focuses the resulting beam to a 0.4 μm (RMS) beam diameter with 62 pm-rad normalized emittance at a distance of 20 mm from the cathode. The compact nature of this lens provides a compelling source for dielectric laser accelerator (DLA) beamlines, ultrafast electron diffraction, or ultrafast electron microscopy. Driven by a 220 fs, 1960 nm pulsed laser beam, electron currents up to 28 electrons/pulse at 100 kHz are demonstrated. The electron bunch length is 540 ± 50 fs for photocurrents of <1 electron/pulse, increasing to 700 ± 80 fs for 28 electrons/pulse, as measured by cross correlation with a 220 fs pulsed laser beam. The maximum 5D peak brightness is measured to be 6.8 × 1013 A/(m2 rad2) at 28 electrons/pulse. These results represent a significant step toward developing practical benchtop-sized linear accelerators based on DLA technology or compact ultrafast electron microscopy and diffraction applications.

Optimization of SIMS analytical parameters for water content measurement of olivine

Secondary ion mass spectrometry (SIMS) has a wide range of applications in Earth Science research, thanks to its high precision and sensitivity, and its capacity in direct insitu micromeasurement. The technique is operated in ultra‐high vacuum (UHV) conditions, especially for the measurement of volatiles such as hydrogen, or the water content in nominally anhydrous minerals (NAMs). To minimize the water background and obtain accurate and precise water contents in NAMs (eg, olivine) critical parameters such as presputtering time, field aperture (FA), dynamic transfer on/off, and primary beam current intensity were investigated for a CAMECA IMS 1280‐HR system. When the chamber vacuum reaches approximately 2 × 10−9 mbar, we set the DTOS OFF, raster size to 50 μm and primary beam current to 5 nA, and used 2000 μm FA and 170‐second presputtering time. Consequently, an approximately 1.2 ppmw water background and 3.6 ppmw limit of detection (LOD) were yielded, from analyzing the San Carlos olivine. Meanwhile, the water content and homogeneity of a range of olivine minerals were characterized for potential use as reference materials for SIMS water content measurement. Olivine water content calibration curve was also established by comparing the Fourier transform infrared (FTIR) results with the SIMS‐measured 16O1H−/16O− ratios. Accuracy and precision of water content measurement were estimated to be better than approximately 10% in this study.

Design and Fabrication of a Push-Pull Electrostatic Actuated Cantilever Waveguide Scanner.

The paper presents a novel fully integrated MEMS-based non-resonating operated 2D mechanical scanning system using a 1D push-pull actuator. Details of the design, fabrication and tests performed are presented. The current design utilizes an integrated electrostatic push-pull actuator and a SU-8 rib waveguide with a large core cross section (4 μm in height and 20 μm in width) in broadband single mode operation (λ = 0.4 μm to 0.65 μm). We have successfully demonstrated a 2D scanning motion using non- resonating operation with 201 Hz in vertical direction and 20 Hz in horizontal direction. This non-resonating scanner system has achieved a field of view (FOV) of 0.019 to 0.072 radians in vertical and horizontal directions, with the advantage of overcoming its frequency shift caused by fabrication uncertainties. In addition, we observed two fundamental resonances at 201 and 536 Hz in the vertical and horizontal directions with corresponding displacements of 130 and 19 μm, or 0.072 and 0.0105 radian field of view operating at a +150 V input. A gradient index (GRIN) lens is placed at the end of the waveguide to focus the diverging beam output from the waveguide and a 20 μm beam diameter is observed at the focal plane. The transmission efficiency of the waveguide is slightly low (~10%) and slight tensile residual stress can be observed at the cantilever portion of the waveguide due to inherent imperfections in the fabrication process.

Trace Element Mapping of Copper- and Zinc-Rich Black Smoker Chimneys from Brothers Volcano, Kermadec Arc, Using Synchrotron Radiation XFM and LA-ICP-MS

High-resolution trace element mapping (2 µm beam) was performed by synchrotron radiation X-ray fluorescence microscopy (SXFM) on Cu- and Zn-rich chimneys from Brothers volcano, Kermadec arc. The maps cover 84- to 136-mm2 cross sections of the inner chimney walls and document the distribution of Fe, Cu, Zn, As, Se, Sr, Pb ± Ga, Au, Bi, and U. Comparative element maps were generated by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) at a lower resolution (47 µm beam), which additionally measured Co, Ni, Mo, Ag, Cd, In, Sn, Sb, Ba, Au, Tl ± V, Te, and Bi. In two Zn-rich chimneys, Cu distribution varies from Cu-bearing sphalerite with chalcopyrite disease to distinct chalcopyrite-lined channels, implying a progression of chalcopyrite replacement of sphalerite. Conversely, the two Cu-rich chimneys have different styles of massive chalcopyrite lining their conduits. The first displays elongate chalcopyrite grains that radiate into and infill the conduit; these radial grains may be related to decreased fluid flow during sealing of the chimney at both its top and bottom. The second style involves multiple, concentric chalcopyrite laminations (0.25–1 mm) inside the conduit, which progressively narrowed the orifice as they were deposited. Fine (15–40 µm) trace element rings are revealed within and between laminations that exhibit variable contents and distributions of Co, Ni, Zn, As, Se, Mo, Ag, Cd, Sn, Te, Au, Tl, Pb, Bi, and U. The presence of U in the rings specifically indicates seawater ingress into the chimney interior despite it vigorously discharging 274°C fluids at the time of sampling. During these periodic seawater incursions, rapidly changing chemical gradients within the chimney wall induce the instantaneous precipitation of metals from the vent fluid. Thus, the trace element rings are a proxy for the secular evolution of vent fluid compositions. We compared enrichment factors of trace element rings to those of fumarole condensates studied at subaerial arc and rift volcanoes and molten S pooled atop a submarine back-arc volcano. Our enrichment factors show remarkable consistency with the other volcanoes and indicate Au, Te, Bi, Cu, Ag, and Se in Brothers’ chimneys were magmatically derived.

High-speed raster-scanning synchrotron serial microcrystallography with a high-precision piezo-scanner.

The Frontier Microfocus Macromolecular Crystallography (FMX) beamline at the National Synchrotron Light Source II with its 1 µm beam size and photon flux of 3 × 1012 photons s-1 at a photon energy of 12.66 keV has reached unprecedented dose rates for a structural biology beamline. The high dose rate presents a great advantage for serial microcrystallography in cutting measurement time from hours to minutes. To provide the instrumentation basis for such measurements at the full flux of the FMX beamline, a high-speed, high-precision goniometer based on a unique XYZ piezo positioner has been designed and constructed. The piezo-based goniometer is able to achieve sub-100 nm raster-scanning precision at over 10 grid-linepairs s-1 frequency for fly scans of a 200 µm-wide raster. The performance of the scanner in both laboratory and serial crystallography measurements up to the maximum frame rate of 750 Hz of the Eiger 16M's 4M region-of-interest mode has been verified in this work. This unprecedented experimental speed significantly reduces serial-crystallography data collection time at synchrotrons, allowing utilization of the full brightness of the emerging synchrotron radiation facilities.

Photothermal-induced frequency stabilization of a solid-state monolithic Nd:YVO4 laser

We report on a novel frequency stabilization method of a monolithic solid-state microchip laser. Here, a Nd:YVO4/YVO4 laser was constructed with an additional erbium and ytterbium co-doped phosphate glass (Er:Glass) incorporated into the resonator. By illuminating the Er:Glass with an intensity modulated auxiliary 1.55 µm beam controlled photothermal-induced optical path-length changes of the resonator were observed, and utilized for frequency stabilization of the main emission of the solid-state 1064 nm laser. Error signal was obtained from beating the emission with an identical, passively stabilized laser. The presented laser stabilization technique provides a relative frequency stability at the level of 4.5 × 10−12@10s, without affetcing the output power of the 1064 nm laser.

Beam Diameter Dependence of Performance in Thick-Layer and High-Power Selective Laser Melting of Ti-6Al-4V.

A 400 W high-power laser was used to fabricate 200-µm-thick Ti-6Al-4V samples to evaluate the effects of small (50 μm) and large (200 μm) beam diameter on density, microstructure and mechanical properties. A series of single-track experiments demonstrated that it was challenging for the small-beam laser to fabricate smooth and defect-free scan tracks. A larger beam diameter efficiently avoided process instability and provided a more stable and uniform melt pool. By increasing the beam diameter, the density of multilayer samples reached 99.95% of the theoretical value, which is much higher than that achieved with the small beam diameter. However, it was difficult to completely eliminate defects due to serious spatter and evaporation. Moreover, all of the generated samples had relatively coarse surfaces. For the large beam diameter of 200 µm, the optimal yield strength, ultimate tensile strength and elongation were 1150 MPa, 1200 MPa and 8.02%, respectively. In comparison, the small beam diameter of 50 µm resulted in values of 1035 MPa, 1100 MPa and 5.91%, respectively. Overall, the large-diameter laser is more suitable for high-power selective laser melting (SLM) technology, especially for thick layers.

A novel RF MEMS switch on frequency reconfigurable antenna application

This paper presents the design, analysis, simulation of a novel radio-frequency micro electromechanical system (RF MEMS) switch on the frequency reconfigurable antenna application. The switch uses coplanar waveguide transmission line for signal transmission, which designed with special mechanical structures, the size of the switch beam is 320 × 120 μm2. The design of RF MEMS switch was simulated using ANSYS. Its simulation voltage is 14 V for 1 µm beam thickness. The electromagnetic performance is optimized and computed by ANSYS EM software. The switch working bandwidth is 40 GHz, the insertion loss is 0.1 dB, return loss of 30 dB and isolation of 26 dB over 30 GHz. In the frequency band, the isolation degree more than 15 dB, and the maximum isolation is 45.3 dB. The switch is mounted on the antenna, and the frequency of the antenna can be reconstructed by using ANSYS EM simulation.

A large area diamond-based beam tagging hodoscope for ion therapy monitoring

The MoniDiam project is part of the French national collaboration CLaRyS (Contrôle en Ligne de l’hAdronthérapie par RaYonnements Secondaires) for on-line monitoring of hadron therapy. It relies on the imaging of nuclear reaction products that is related to the ion range. The goal here is to provide large area beam detectors with a high detection efficiency for carbon or proton beams giving time and position measurement at 100 MHz count rates (beam tagging hodoscope). High radiation hardness and intrinsic electronic properties make diamonds reliable and very fast detectors with a good signal to noise ratio. Commercial Chemical Vapor Deposited (CVD) poly-crystalline, heteroepitaxial and monocrystalline diamonds were studied. Their applicability as a particle detector was investigated using α and β radioactive sources, 95 MeV/u carbon ion beams at GANIL and 8.5 keV X-ray photon bunches from ESRF. This facility offers the unique capability of providing a focused (~1 μm) beam in bunches of 100 ps duration, with an almost uniform energy deposition in the irradiated detector volume, therefore mimicking the interaction of single ions. A signal rise time resolution ranging from 20 to 90 ps rms and an energy resolution of 7 to 9% were measured using diamonds with aluminum disk shaped surface metallization. This enabled us to conclude that polycrystalline CVD diamond detectors are good candidates for our beam tagging hodoscope development. Recently, double-side stripped metallized diamonds were tested using the XBIC (X Rays Beam Induced Current) set-up of the ID21 beamline at ESRF which permits us to evaluate the capability of diamond to be used as position sensitive detector. The final detector will consist in a mosaic arrangement of double-side stripped diamond sensors read out by a dedicated fast-integrated electronics of several hundreds of channels.

Metallurgical and tribological investigation of micro-scale fibre laser-based surface hardening

This work presents a comprehensive analysis of the mechanical, metallurgical and tribological responses of the various micro-scale laser hardened patterns of EN-8 steel at different process conditions. A 100 W continuous wave fibre laser with ~200-900 µm beam diameter was used for micro-scale hardening. EBSD was used to investigate the micro-structure and the hardness values were measured using micro hardness tester (Shimadzu-HMV). Additionally, to measure the tribological response, four different hardened patterns were analysed using the 'pin on disk setup' (DUCOM wear and friction monitor TR-20LE). The preliminary results revealed improved surface hardness values with increase in percentage overlap due to the formation of martensite. Furthermore, it was observed that the average wear rate of hardened specimen decreases by ~91% as compared to the unhardened specimen. The results revealed an inverse relationship between friction force and percent-hardened area, with minimum friction force obtained for a fully hardened pattern.

Experimental optimisation of the X-ray energy in microbeam radiation therapy

Microbeam radiation therapy has demonstrated superior normal tissue sparing properties compared to broadbeam radiation fields. The ratio of the microbeam peak dose to the valley dose (PVDR), which is dependent on the X-ray energy/spectrum and geometry, should be maximised for an optimal therapeutic ratio. Simulation studies in the literature report the optimal energy for MRT based on the PVDR. However, most of these studies have considered different microbeam geometries to that at the Imaging and Medical Beamline (50 μm beam width with a spacing of 400 μm). We present the first fully experimental investigation of the energy dependence of PVDR and microbeam penumbra. Using monochromatic X-ray energies in the range 40–120 keV the PVDR was shown to increase with increasing energy up to 100 keV before plateauing. PVDRs measured for pink beams were consistently higher than those for monochromatic energies similar or equivalent to the average energy of the spectrum. The highest PVDR was found for a pink beam average energy of 124 keV. Conversely, the microbeam penumbra decreased with increasing energy before plateauing for energies above 90 keV. The effect of bone on the PVDR was investigated at energies 60, 95 and 120 keV. At depths greater than 20 mm beyond the bone/water interface there was almost no effect on the PVDR. In conclusion, the optimal energy range for MRT at IMBL is 90–120 keV, however when considering the IMBL flux at different energies, a spectrum with 95 keV weighted average energy was found to be the best compromise.

Micromachined microbeams made from porous silicon for dynamic and static mode sensing

Abstract Through a controlled variation of the applied current during porous silicon formation, newly developed processes enable previously unattainable structural integrity of all-mesoporous silicon microelectromechanical systems (MEMS) structures. Such structures are desirable for applications such as sensing where the large surface area and low Young’s modulus of the high porosity layer enable ultra-high sensitivity detection of adsorbed species. In this work, micromachined all-mesoporous silicon microbeams were released, allowing both the dynamic and static sensing modes to be studied using such porous structures. Resonant frequencies (50–250 kHz) of released doubly clamped porous silicon microbeams were measured, allowing mechanical properties to be extracted. Static mode sensing of vapour at the 1100 ppm level was also performed, with the released porous silicon cantilevers showing a significant 6.5 μm (3.7% of a 175 μm beam length) and repeatable deflection after exposure.

Low Efficiency Upconversion Nanoparticles for High-Resolution Coalignment of Near-Infrared and Visible Light Paths on a Light Microscope.

The combination of near-infrared (NIR) and visible wavelengths in light microscopy for biological studies is increasingly common. For example, many fields of biology are developing the use of NIR for optogenetics, in which an NIR laser induces a change in gene expression and/or protein function. One major technical barrier in working with both NIR and visible light on an optical microscope is obtaining their precise coalignment at the imaging plane position. Photon upconverting particles (UCPs) can bridge this gap as they are excited by NIR light but emit in the visible range via an anti-Stokes luminescence mechanism. Here, two different UCPs have been identified, high-efficiency micro540-UCPs and lower efficiency nano545-UCPs, that respond to NIR light and emit visible light with high photostability even at very high NIR power densities (>25 000 Suns). Both of these UCPs can be rapidly and reversibly excited by visible and NIR light and emit light at visible wavelengths detectable with standard emission settings used for Green Fluorescent Protein (GFP), a commonly used genetically encoded fluorophore. However, the high efficiency micro540-UCPs were suboptimal for NIR and visible light coalignment, due to their larger size and spatial broadening from particle-to-particle energy transfer consistent with a long-lived excited state and saturated power dependence. In contrast, the lower efficiency nano-UCPs were superior for precise coalignment of the NIR beam with the visible light path (∼2 μm versus ∼8 μm beam broadening, respectively) consistent with limited particle-to-particle energy transfer, superlinear power dependence for emission, and much smaller particle size. Furthermore, the nano-UCPs were superior to a traditional two-camera method for NIR and visible light path alignment in an in vivo Infrared-Laser-Evoked Gene Operator (IR-LEGO) optogenetics assay in the budding yeast Saccharomyces cerevisiae. In summary, nano-UCPs are powerful new tools for coaligning NIR and visible light paths on a light microscope.

Fractional laser-assisted drug uptake: Impact of time-related topical application to achieve enhanced delivery.

Ablative fractional laser (AFXL) is acknowledged to increase uptake of topically applied agents in skin. AFXL channels gradually close over time, which may impair this capability. The time frame for applying a drug after AFXL exposure remains to be established. The aim of this study, was to investigate the importance of time-related topical application after AFXL exposure and to relate resultant uptake in skin with AFXL channel morphology and skin integrity. Buttock skin of healthy volunteers (n = 11) was exposed to 10,600 nm fractional CO2 laser using 5% density, 120 μm beam diameter, 15 mJ pulse energy. Sodium fluorescein (NaF) a small, hydrophilic molecule (370 MW, log P = -1.52) was applied under standardized conditions at specific time points after laser exposure (0, 2, 5, 10, 30, 60, 90 minute, 6, 24, and 48 hours). Fluorescence photography collected fluorescence images up to 180 minute after NaF application. Optical coherence tomography (OCT) assessed AFXL channel dimensions and transepidermal water loss (TEWL) estimated loss of skin integrity. Fluorescence intensities (FI) were significantly elevated when NaF was applied up to 6 hours after laser exposure compared to non-laser-processed skin (median FI 1947 arbitrary units [interquartile range 1,246-3,560] versus 1,004 [350-1,538], P < 0.02). The highest FI occurred when NaF was applied within 30 minute after laser exposure and similar FI were reached for applications at 0, 2, 5, 10, and 30 minute after AFXL exposure (0 minute: 3,866 [3,526-4,575], 30 minute: 3,775 AU [3,070-4,484], P > 0.1). NaF application later than 30 minute after AFXL exposure resulted in gradually decreasing FI, becoming similar to intact skin when applied at 24-48 hours after AFXL exposure (P > 0.2). OCT images demonstrated that AFXL channels closed over time (100% [100-100%] open up to 30 minute, 75% [4-86%] at 6 hours and 3% [0-15%] at 24-48 hours after AFXL exposure). TEWL measurements proved loss of skin integrity up to 6 hours after AFXL exposure, while integrity was similar in laser-exposed and non-laser-exposed skin at 24-48 hours. The time frame to maintain enhanced drug delivery sustained for several hours after AFXL exposure, corresponding to channel morphology and loss of skin integrity. Lasers Surg. Med. 49:348-354, 2017. © 2016 Wiley Periodicals, Inc.

Laser induced photochemical reaction for establishment of quantitative median nerve injury model in rats

Objective To establish laser induced photochemical quantitative median nerve injury model in rats and validate the feasibility of this model. Methods Sixteen Sprague-Dawley rats were randomly divided into 4 groups based on the duration of laser irradiation to their median nerves: control group, 10 s group, 20 s group and 40 s group. A 5 mm segment of the right median nerves at the proximal upper arm was exposed 5 minutes after Etythrosine injection (32.5 mg/kg) via the tail vein. The exposed nerve was uniformly irradiated by a laser with 532 nm wavelength, 170 mW intensity and 200 μm beam diameter. Behavior of the rats, including grasping ability and foot licking, were observed daily in the first week and weekly for 5 more weeks after the injury. Two weeks after the injury, median nerve samples distal to the laser irradiation site were harvested from 2 rats of each group for toluidine blue staining to observe the histological changes. Results All the rats survived the procedure and various behaviors were observed. Limitation of grasping ability and frequent licking of the foot on the injury side were observed in rats of all three experimental groups from day 1 to day 7. This observation was most remarkable in rats of the 40 s group. These behaviors were not seen in rats of the control group. From 2 to 4 weeks, the functional status continued to decline. From 5 to 6 weeks, rats in the 10 s and 20 s groups started to show recovery of grasping activity, whereas in the 40 s group one rat had partial grasping activity while the other one had no obvious activity. Histological examination of nerve samples 2 weeks after laser irradiation showed demyelination changes of the myelinated fibers, being most pronounced in the 40 s group while no changes in the control group. Conclusion After photo initiator injection, laser irradiation with different doses can cause varying degrees of nerve injury that involves motor, sensory and sympathetic functions of the nerve. Photo-chemically induced partial injury of a single nerve in rats has relatively high success rate and reproducibility. The extent of injury can be modulated quantitatively. Key words: Photochemistry; Models, animal; Median nerve; Quantitative injury

Electro-optic beam deflection based on a lithium niobate waveguide with microstructured serrated electrodes.

We report on electro-optic beam deflection using an annealed proton exchange waveguide in lithium niobate (LN) with microstructured serrated array electrodes. Due to the electro-optic effect of the LN material, the experimental results show that the beam deflection and modulation of the LN waveguide can be realized with relatively low voltages. The total length of the serrated prism array electrodes structure is ∼5 mm. With 20 V applied to the electrodes of 50, 100, and 150 μm wide waveguides, ∼1.28, ∼0.96, and ∼0.64 μm beam deflections were obtained, respectively, which are in accordance with theoretical simulation. This configuration can be potentially applied in optical beam scanning, high-speed switches, and optical beam smoothing technology.

Advancements and best practices for analysis and correlation of tephra and cryptotephra in ice

Geochemical analysis of fine grained (<20 μm) tephra found in ice cores is inherently difficult, due to the typically low number and small size of available particles. Ice core tephra samples require specialized sample preparation techniques to maximize the amount of information that can be gained from these logistically limited samples that may provide important chronology to an ice record, as well as linking glacial, marine and terrestrial sediments. We have developed a flexible workflow for preparation of tephra and cryptotephra samples to allow accurate and robust geochemical fingerprinting, which is fundamental to tephrochronology. The samples can be prepared so that secondary electron imagery can be obtained for morphological characterization of the samples to ensure that the sample is tephra-bearing and then the sample can be further prepared for quantitative electron microprobe analysis using wavelength dispersive techniques (EMP-WDS), scanning electron microscopy with energy dispersive spectrometry (SEM-EDS), laser ablation inductively coupled mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS). Some samples may be too small for typical instrumentation conditions to be used (i.e. 20 μm beam on the EMP) to analyze for geochemistry and we present other techniques that can be employed to obtain accurate, although less precise, geochemistry. Methods include analyzing unpolished tephra shards less than 5 μm in diameter with a 1 μm beam on an SEM; using the “broad beam overlap” EMP method on irregular particles less than 20 μm in diameter, and analyzing microlitic shards as well as aphyric shards using EMP to increase the number of analyzed shards in low abundance tephra layers. The methods presented are flexible enough to be employed in other geological environments (terrestrial, marine and glacial) which will help maximize and integrate multiple environments into the overall tephra framework.

Oversolubility in the microvicinity of solid–solution interfaces

Water-solid interactions at the macroscopic level (beyond tens of nanometers) are often viewed as the coexistence of two bulk phases with a sharp interface in many areas spanning from biology to (geo)chemistry and various technological fields (membranes, microfluidics, coatings, etc.). Here we present experimental evidence indicating that such a view may be a significant oversimplification. High-resolution infrared and Raman experiments were performed in a 60 × 20 μm(2) quartz cavity, synthetically created and initially filled with demineralized water. The IR mapping (3 × 3 μm(2) beam size) performed using the SOLEIL synchrotron radiation source displays two important features: (i) the presence of a dangling free-OH component, a signature of hydrophobic inner walls; (ii) a shift of the OH-stretching band which essentially makes the 3200 cm(-1) sub-band predominate over the usual main component at around 3400 cm(-1). Raman maps confirmed these signatures (though less marked than IR's) and afforded a refined spatial distribution of this interfacial signal. This spatial resolution, statistically treated, results in a puzzling image of a 1-3 μm thick marked-liquid layer along the entire liquid-solid interface. The common view is then challenged by this strong evidence that a μm-thick layer analogous to an interphase forms at the solid-liquid interface. The thermodynamic counterpart of the vibrational shifts amounts to around +1 kJ mol(-1) at the interface with a rapidly decreasing signature towards the cavity centre, meaning that vicinal water may form a reactive layer, of micrometer thickness, expected to have an elevated melting point, a depressed boiling temperature, and enhanced solvent properties.

Frequency characteristics of far-detuned parametric four-wave mixing in Rb.

We have investigated the frequency characteristics of the coherent 420 nm beam generated via parametric four-wave mixing (FWM). A single, high-power 778 nm laser is directed through a high-density rubidium cell with a detuning of 1 THz from the intermediate state, generating fields at 420 nm and 5.23 μm through FWM. The frequency of the 420 nm light has been found to shift as the excitation laser is tuned. The measured frequency shift ratio of 1.87±0.04 corresponds with the selection of a different velocity class at each excitation frequency, implying that the 5.23 μm beam frequency is correspondingly shifted. The 420 nm light has been tuned over a range of 1 GHz. This parametric FWM process has potential application as a tunable photon source at novel wavelengths.