Raman spectroscopy with an integrated arrayed-waveguide grating

An integrated arrayed-waveguide grating fabricated in silicon-oxynitride technology is applied to Raman spectroscopy. After its validation by reproducing the well-known spectrum of cyclohexane, polarized Raman spectra are measured of extracted human teeth containing localized initial carious lesions. Excellent agreement is obtained between the spectra of healthy and carious tooth enamel measured with our integrated device and spectra recorded using a conventional Raman spectrometer. Our results represent a step toward the realization of compact, hand-held, integrated spectrometers, e.g. for the detection of dental caries at an early stage.     

Laurane-derived sesquiterpenes from the marine red alga Laurencia tristicha (Rhodomelaceae)

Two new stereoisomers of laurane-derived brominated sesquiterpenes, 4-bromolaur-11-en-1,10alpha-diol (1) and 4-bromolaur-11-en-1,10beta-diol (2), one new natural product, laur-11-en-1,10alpha-diol (3), together with 11 known compounds (4-14) were isolated and identified from the organic extract of the marine red alga Laurencia tristicha. Their structures and relative stereochemistry were established by analysis of mass and NMR spectroscopic techniques.     

Precision of Raman depolarization and optical attenuation measurements of sound tooth enamel

The demineralization of enamel that is associated with early caries formation affects the optical properties of the enamel. Polarized Raman spectroscopy and optical coherence tomography have been used to detect these changes and potentially offer a means to detect and monitor early caries development. The total optical attenuation coefficient as measured by optical coherence tomography and the polarization anisotropy of the Raman peak arising from the symmetric ν₁ vibration of at approximately 959 cm⁻¹ have been demonstrated as being sensitive markers of early caries. This ex vivo study on extracted human teeth demonstrates that these measurements can be made with reasonable precision with concomitantly good repeatability and reproducibility in sound enamel. Such reliability is crucial for these techniques to have a practical clinical value.     

Fiber-optics implementation of the Deutsch-Jozsa and Bernstein-Vazirani quantum algorithms with three qubits

We report on a fiber-optics implementation of the Deutsch-Jozsa and Bernstein-Vazirani quantum algorithms for 8-point functions. The measured visibility of the 8-path interferometer is about 97.5%. Potential applications of our setup to quantum communication or cryptographic protocols using several qubits are discussed.     

Experimental error filtration for quantum communication over highly noisy channels

Error filtration is a method for encoding the quantum state of a single particle into a higher dimensional Hilbert space in such a way that it becomes less sensitive to noise. We have realized a fiber optics demonstration of this method and illustrated its potentialities by carrying out the optical part of a quantum key distribution scheme over a line whose phase noise is too high for a standard implementation of BB84 to be secure. By filtering out the noise, a bit error rate of 15.3% +/- 0.1%, which is beyond the security limit, can be reduced to 10.6% +/- 0.1%, thereby guaranteeing the cryptographic security.     

Interactions of particles and microbubbles with turbulence

Dilute, dispersed two-phase flows arise in many contexts ranging from solid particles or droplets in gas flows to bubbles in liquids. Many of the flows of interest are turbulent, which presents a complex problem to analyze or to determine the dominant physical processes contributing to the observed phenomena. Advances in experimental techniques have made it possible to measure directly turbulent and particle velocity fluctuations in dilute systems. This has provided a counterpart to advances in computational and analytical models and a basis on which to test these models. Three specific areas are considered: the fluctuating forces on an individual particle in an unsteady flow, the response of a solid particle to a turbulent air flow, and the corresponding response of a small bubble in turbulent liquid flows. Results from direct numerical simulations are presented for each of these, including the nonuniform distribution of particles generated by local instantaneous features of the flow. The issue of turbulence modulation at low to moderate void fractions is discussed.     

Excitations from a Bose-Einstein condensate of magnons in coupled spin ladders

The weakly coupled quasi-one-dimensional spin ladder compound (CH3)2CHNH3CuCl3 is studied by neutron scattering in magnetic fields exceeding the critical field of Bose-Einstein condensation of magnons. Commensurate long-range order and the associated Goldstone mode are detected and found to be similar to those in reference to spin-dimer materials. However, for the upper two massive magnon branches, the observed behavior is totally different, culminating in a drastic collapse of excitation bandwidth beyond the transition point.     

Excitations in a four-leg antiferromagnetic Heisenberg spin tube

Inelastic neutron scattering is used to investigate magnetic excitations in the quasi-one-dimensional quantum spin-liquid system Cu(2)Cl(4).D(8)C(4)SO(2). Contrary to previously conjectured models that relied on bond-alternating nearest-neighbor interactions in the spin chains, the dominant interactions are actually next-nearest-neighbor in-chain antiferromagnetic couplings. The appropriate Heisenberg Hamiltonian is equivalent to that of a S=1/2 4-leg spin-tube with almost perfect one dimensionality and no bond alternation. A partial geometric frustration of rung interactions induces a small incommensurability of short-range spin correlations.     

Pigment identification in artwork using graphite furnace atomic absorption spectrometry

The use of a sampling technique is described for the identification of metals from inorganic pigments in paint. The sampling technique involves gently contacting a cotton swab with the painted surface to physically remove a minute quantity (∼1-2 μg) of pigment. The amount of material removed from the painted surface is invisible to the unaided eye and does not cause any visible effect to the painted surface. The cotton swab was then placed in a 1.5 ml polystyrene beaker containing HNO₃ to extract pigment metals prior to analysis using graphite furnace atomic absorption spectrometry (GFAAS). GFAAS is well suited for identifying pigment metals since it requires small samples and many pigments consist of main group elements (e.g. Al) as well as transition metals (e.g. Zn, Fe and Cd). Using Cd (cadmium red) as the test element, the reproducibility of sampling a paint surface with the cotton swab was approximately 13% in either a water or oil medium. To test the feasibility of cotton sampling for pigment identification, samples were obtained from paintings (watercolour and oil) of a local collection. Raman spectra provided complementary information to the GFAAS, which together are essential for positive identification of some pigments. For example, GFAAS indicated the presence of Cu, but the Raman spectra positively identified the modern copper pigment phthalocyanine green (Cu(C₃₂Cl₁₆N₈). Both Raman spectroscopy and GFAAS were useful for identifying ZnO as a white pigment.