Investigation of Brillouin effects in small-core holey optical fiber: lasing and scattering

We demonstrate for what is believed to be the first time a Brillouin laser based on a holey fiber (HF). Using a simple Fabry-Perot resonator scheme containing a 73.5-m-long highly nonlinear HF with an effective area of 2.85 microm(2) , we obtain a threshold of 125 mW and a slope efficiency of ~70% . Stimulated and spontaneous Brillouin scattering effects are investigated in the HF, and we show that the high lasing threshold is due mainly to reduction of the effective gain coefficient caused by structural nonuniformity along the fiber length.     

Generation of quaternary centers by reductive cross-coupling: shifting of regioselectivity in a subset of allylic alcohol-based coupling reactions

Regioselective titanium alkoxide-mediated reductive cross-coupling reactions of allylic alcohols with vinylsilanes and imines have previously been demonstrated to proceed with allylic transposition by formal metallo-[3,3]-rearrangement [thought to proceed by a sequence of: (1) directed carbometalation, and (2) syn-elimination]. While many examples have been described that support this reaction path, a collection of substrates have recently been identified that react by way of an alternative pathway, delivering a concise convergent route to coupled products bearing a quaternary center.     

Environmental analysis of organic compounds in water using solid phase micro extraction

Solid Phase Micro Extraction (SPME) involves exposing a fused silica fiber coated with stationary phase to a contaminated water sample. The organic analytes become partitioned between the stationary phase and the water and when equilibrium is reached the fiber is removed from the solution and the analytes are thermally desorbed in the injector of a gas chromatograph. The fiber is contained in a syringe to facilitate handling. Factors which affect linear range, limit of detection, and total analysis time are discussed with regard to the development of a method for analysis of volatile compounds in environmental water samples. The sensitivity of the method was determined by the thickness of the film of stationary phase; the equilibration time, however, increased with the film thickness, although it can be minimized by use of a cross-shaped stirrer bar. Increasing the thickness of stationary phase in the analytical column enables the cryofocusing temperature to be increased from ?40 to ?15°C. With an ion trap mass spectrometer, detection limits required by the US Environmental Protection Agency are met for all compounds except chloromethane and chloroethane. The method has been applied to environmental water samples.     

Effects of lipopolysaccharide-induced inflammation on expression of growth-associated genes by corticospinal neurons

Background  

Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation.     

Raman effects in a highly nonlinear holey fiber: amplification and modulation

We experimentally demonstrate that a short length of highly nonlinear holey fiber (HF) can be used for strong L(+) -band (1610-1640-nm) Raman amplification and ultrafast signal modulation. We use a pure silica HF with an effective area of just 2.85mum(2) at 1550 nm, which yields an effective nonlinearity ~15 times higher than in conventional silica dispersion-shifted fiber. Using a 75-m length of this fiber, we obtained internal Raman gains of more than 42 dB and a noise figure of ~6 dB under a forward single-pump scheme, and the Raman gain coefficient was experimentally estimated to be 7.6 chi 10(-14)m/W . Also, an 11-dB signal extinction ratio in a Raman-induced all-optical modulation experiment was achieved with the same fiber.     

2R-regenerative all-optical switch based on a highly nonlinear holey fiber

We report the fabrication of a highly nonlinear holey fiber made from pure silica with an effective area of just ~2.8mu;m(2) at 1550 nm. We believe this to be the smallest effective area yet measured for a holey fiber at 1550 nm. We also report the operation of a 2R regenerative optical switch based on just 3.3 m of the fiber that is shown to have 30 times the nonlinear figure of merit of previous devices based on dispersion-shifted fiber.     

UV generation in a pure-silica holey fiber

We report supercontinuum generation extending to 300 nm in the UV from a pure-silica holey fiber. The broad spectrum was obtained by launching ultra-short pulses (150 fs, 10 nJ at 820 nm) from an amplified Ti:sapphire laser. The extension of holey-fiber-based supercontinuum generation into the UV should prove to be of immediate application in spectroscopy. By slightly detuning the launch conditions we excited a higher order spatial mode, which produced a narrower supercontinuum, but with enhanced conversion efficiency at a series of blue/UV peaks around 360 nm. We present numerical simulations, which suggest that differences in the dispersion profiles between the modes are an important factor in explaining this enhancement. In a related experiment, using the same laser source and fiber, we demonstrate a visible supercontinuum from several subsidiary cores, with distinct colours in each core. The subsidiary cores were excited by an appropriate input coupling. Fabrication of a fiber with a range of core sizes (dispersion profiles) for tailored supercontinuum generation can therefore be envisaged for practical applications. PACS 42.72.Bj; 42.79.Nv; 42.81.Dp     

Experimental investigation of the flow induced by artificial cilia

The fluid transport produced by rectangular shaped, magnetically actuated artificial cilia of 70 μm length and 20 μm width was determined by means of phase-locked Micro Particle Image Velocimetry (μPIV) measurements in a closed microfluidic chamber. The phase-averaged flow produced by the artificial cilia reached up to 130 μm s(-1) with an actuation cycle frequency of 10 Hz. Analysis of the measured flow data indicate that the present system is capable of achieving volume flow rates of V[combining dot above](cilia) = 14 ± 4 μl min(-1) in a micro channel of 0.5 × 5 mm(2) cross-sectional area when no back pressure is built up. This corresponds to an effective pressure gradient of 6 ± 1 Pa m(-1), which equals a pressure difference of 0.6 ± 0.1 mPa over a distance of 100 μm between two rows of cilia. These results were derived analytically from the measured velocity profile by treating the cilia as a thin boundary layer. While the cilia produce phase-averaged velocities of the order of O(10(2)μm s(-1)), time-resolved measurements showed that the flow field reverses two times during one actuation cycle inducing instantaneous velocities of up to approximately 2 mm s(-1). This shows that the flow field is dominated by fluid oscillations and flow rates are expected to increase if the beating motion of the cilia is further improved.