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Nanocomposites based on poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) with untreated clay were prepared in one step by reactive melt extrusion. Chemical reactions took place between the polymer matrices, the inorganic clay particles, and three reactive agents, leading to the PVDF/PMMA/clay nanocomposites. The microstructure characterizations were carried out by differential scanning calorimetry and wide-angle X-ray scattering (WAXS). The mechanical behavior was investigated by tensile experiments, impact tests, and microhardness measurements. The morphological characterization was carried out by optical and atomic force microscopy (AFM). The decrease of the melting and crystallization temperatures of the PVDF with the increasing PMMA content is attributed to the interactions between the oxygen of the PMMA carbonyl group and the PVDF's hydrogen atom. WAXS analysis shows that there is neither an intercalation step nor total exfoliation in any composition. As the PMMA content increases, WAXS diagrams show either the PVDF α-crystallographic form, both, α- and β-forms, or only the β-form. For PMMA contents higher than 40 wt%, the materials became amorphous. The microhardness of the samples decrease for a PMMA content up to 20 wt%. The study by optical microscopy and AFM illustrates the significant effect in the presence of clay on the film's surface morphology. [ABSTRACT FROM AUTHOR]

Rubidium vapor is loaded into hypocycloidal core shaped Kagome hollow-core photonic crystal fiber (HC-PCF) with the wall of its inner core coated with aluminosilicate ceramic (sol-gel). We show that the presence of Rb vapor is maintained for a longer duration when compared to uncoated Kagome HC-PCF. Rb vapor within the hollow-core of a sol-gel coated Kagome HC-PCF is preserved for over 500 h after the source of Rb is halted. And Rb vapor is detected in the sol-gel coated HC-PCF for more than 80 h after the background Rb vapor signal is no longer observed. [ABSTRACT FROM PUBLISHER]

We report on numerical and experimental results on macro bending losses in single-cell Kagome-lattice hollow-core photonic crystal fibers. Fibers with different cladding layer numbers have been investigated. Results show that a cladding with at least two rings produces a reduction in bend sensitivity by more than one order of magnitude relative to a single layer cladding. This result is an original way to confirm the main role played by the inhibiting coupling mechanism in such microstructured fibers. [ABSTRACT FROM PUBLISHER]

Argon micro-plasmas a few centimetres long are generated at low gas pressure (6 mbar) in hollow-core photonic crystal fibres with 100 µm core diameter, using microwave excitation (2.45 GHz) based on a surfatron, with no damage to the host structure. Electromagnetic simulations assist the design of the surfatron cavity, finding optimal conditions for discharge ignition and maintenance. The plasma characterization reveals an electron density in the range 8 × 1014–1015 cm−3 (estimated from a semi-empirical analysis of the power coupled to the plasma, along the axial-direction) and a gas temperature of 1100–1300 K at the centre of the fibre (measured by optical emission spectroscopy diagnostics), thus showing an impressive ionization degree of ∼10−2 for power densities of ∼0.1 MW cm−3. The micro-plasma dynamics is investigated using a self-consistent one-dimensional (radial) fluid model, describing the charged particle and the electron energy transport, the electromagnetic excitation and the gas heating. Model results are used to confirm the diagnostics, revealing an extreme plasma confinement and a steep temperature gradient that give rise to the main operation features of this novel compact UV source. [ABSTRACT FROM AUTHOR]

We review the optical guidance properties of hollow-core photonic crystal fibers. We follow a historical perspective to introduce the two major optical guidance mechanisms that were identified as operating in these fibers: photonic bandgap guidance and inhibited coupling guidance. We then review the modal properties of these fibers and assess the transmission loss mechanisms in photonic bandgap guiding hollow-core photonic crystal fiber. We dedicate a section to a review of the technical basics of hollow-core photonic crystal fiber fabrication and photonic microcell assembly. We review some of the early results on the use of hollow-core photonic crystal fiber for laser guiding micro-sized particles, as well as the generation of stimulated Raman scattering, electromagnetically induced transparency and laser frequency stabilization when the fiber core is filled with a gas-phase material. We conclude this review with a non-exhaustive list of prospects where hollow-core photonic crystal fiber could play a central role. [ABSTRACT FROM AUTHOR]

High harmonic generation (HHG) of intense infrared laser radiation (Ferray et al., J. Phys. B: At. Mol. Opt. Phys. 21:L31, ; McPherson et al., J. Opt. Soc. Am. B 4:595, ) enables coherent vacuum-UV (VUV) to soft-X-ray sources. In the usual setup, energetic femtosecond laser pulses are strongly focused into a gas jet, restricting the interaction length to the Rayleigh range of the focus. The average photon flux is limited by the low conversion efficiency and the low average power of the complex laser amplifier systems (Keller, Nature 424:831, ; Südmeyer et al., Nat. Photonics 2:599, ; Röser et al., Opt. Lett. 30:2754, ; Eidam et al., IEEE J. Sel. Top. Quantum Electron. 15:187, ) which typically operate at kilohertz repetition rates. This represents a severe limitation for many experiments using the harmonic radiation in fields such as metrology or high-resolution imaging. Driving HHG with novel high-power diode-pumped multi-megahertz laser systems has the potential to significantly increase the average photon flux. However, the higher average power comes at the expense of lower pulse energies because the repetition rate is increased by more than a thousand times, and efficient HHG is not possible in the usual geometry. So far, two promising techniques for HHG at lower pulse energies were developed: external build-up cavities (Gohle et al., Nature 436:234, ; Jones et al., Phys. Rev. Lett. 94:193, ) and resonant field enhancement in nanostructured targets (Kim et al., Nature 453:757, ). Here we present a third technique, which has advantages in terms of ease of HHG light extraction, transverse beam quality, and the possibility to substantially increase conversion efficiency by phase-matching (Paul et al., Nature 421:51, ; Ren et al., Opt. Express 16:17052, ; Serebryannikov et al., Phys. Rev. E (Stat. Nonlinear Soft Matter Phys.) 70:66611, ; Serebryannikov et al., Opt. Lett. 33:977, ; Zhang et al., Nat. Phys. 3:270, ). The interaction between the laser pulses and the gas occurs in a Kagome-type Hollow-Core Photonic Crystal Fiber (HC-PCF) (Benabid et al., Science 298:399, ), which reduces the detection threshold for HHG to only 200 nJ. This novel type of fiber guides nearly all of the light in the hollow core (Couny et al., Science 318:1118, ), preventing damage even at intensities required for HHG. Our fiber guided 30-fs pulses with a pulse energy of more than 10 μJ, which is more than five times higher than for any other photonic crystal fiber (Hensley et al., Conference on Lasers and Electro-Optics (CLEO), IEEE Press, New York, ). [ABSTRACT FROM AUTHOR]

Tightly confined light enables a variety of applications ranging from nonlinear light management to atomic manipulation. Photonic-crystal fibres (PCFs) can provide strong guidance in very small cores while simultaneously offering long interaction lengths. However, light confinement in waveguides is usually ultimately limited by diffraction, which tends to spread light away from the waveguiding core, despite its higher refractive index. It was recently demonstrated that such spreading fields can be trapped by a nanometre-scale slot inside a strongly guiding silicon-on-insulator (SOI) waveguide. In this letter we demonstrate the concentration of optical energy within a subwavelength-scale air hole running down the length of a PCF core. The core resembles a submicrometre-diameter tube with a bore diameter of 200 nm or less. The high intensity in an air hole, coupled with long interaction lengths, promises a new class of experiments in light–matter interaction and nonlinear fibre optics. [ABSTRACT FROM AUTHOR]

Brain pathology is a perfect application field for nanotechnologies supporting the concept of nanomedicine. It implies the use of nanosized tools for diagnosis and therapy and finally the switch to nanosized disease. A good illustration is the synergistic association of functional neurosurgery to micro/nanotechnologies. The developments around electrostimulation are a good example of the lower invasivity and better therapeutical efficacy that can be achieved. Nanolevel disease detection and therapy dramatically modifies medical philosophy as well as practice. The demonstration of the validity of the concept of nanomedicine has to be done carefully and this period of validation is a precious time to solve ethical problems. Ethical issues include the problem of disease detection in “healthy patients”; the non medical use of nanotechnologies, and the acceptance of what could be a potentially uncontrollable major modification of the human body. All these items are used against nanotechnologies, thus it will be crucial to inform the public about the state of the art in nanomedicine and about the existing regulations. National and European regulations should be adequate for nanomedicine, provided there is progressive integration instead of a conservative attitude blocking experiments and progress. The European research community has a good opportunity to do that. [ABSTRACT FROM AUTHOR]

Gas-phase materials are used in a variety of laser-based applications-for example, in high-precision frequency measurement, quantum optics and nonlinear optics. Their full potential has however not been realized because of the lack of a suitable technology for creating gas cells that can guide light over long lengths in a single transverse mode while still offering a high level of integration in a practical and compact set-up or device. As a result, solid-phase materials are still often favoured, even when their performance compares unfavourably with gas-phase systems. Here we report the development of all-fibre gas cells that meet these challenges. Our structures are based on gas-filled hollow-core photonic crystal fibres, in which we have recently demonstrated substantially enhanced stimulated Raman scattering, and which exhibit high performance, excellent long-term pressure stability and ease of use. To illustrate the practical potential of these structures, we report two different devices: a hydrogen-filled cell for efficient generation of rotational Raman scattering using only quasi-continuous-wave laser pulses; and acetylene-filled cells, which we use for absolute frequency-locking of diode lasers with very high signal-to-noise ratios. The stable performance of these compact gas-phase devices could permit, for example, gas-phase laser devices incorporated in a‘credit card’or even in a laser pointer. [ABSTRACT FROM AUTHOR]

We report on the experimental observation of electromagnetically induced transparency in V and Λ energy level schemes using counterpropagating coupling and probe beam geometry. The observation was achieved using an acetylene photonic microcell. The conditions required for this observation are explored theoretically, and we show that the use of counterpropagating beams in electromagnetically induced transparency may have applications as a spectroscopic technique where velocity discrimination is desirable. [ABSTRACT FROM AUTHOR]

We report on a technique to pattern the shape of the core surround of a hollow-core photonic crystal fiber. Different shapes are fabricated and a relationship between surface mode location and core surround thickness is experimentally observed. [ABSTRACT FROM PUBLISHER]

Optical feedback from the Fresnel reflection at the air-silica interface of a splice between a hollow core photonic crystal fiber (HC-PCF) and a conventional fiber can cause laser instability or damage. The reported solution consists of the preparation of angle cleaved fibers, spliced together using a filament fusion splicer. A reduction of 44 dB of the return loss is observed. The method will considerably reduce potential damage such as fiber fusion in case of a fiber laser. The method is also demonstrated to decrease the Fabry-Perot effect in setups such as saturable absorption when the spliced HC-PCF is used as a gas cell device. [ABSTRACT FROM PUBLISHER]