We demonstrate supercontinuum generation in a photonic crystal fiber with all-normal group velocity dispersion. Pumping a short section of this fiber with compressed pulses from a compact amplified fiber laser generates a 200 nm bandwidth continuum with typical self-phase-modulation characteristics. We demonstrate that the supercontinuum is compressible to a duration of 26 fs. It therefore has a high degree of coherence between all the frequency components, and is a single pulse in the time domain. A smooth, flat spectrum spanning 800 nm is achieved using a longer piece of fiber.

The x-ray crystal structure of recombinant human renin has been determined. Molecular dynamics techniques that included crystallographic data as a restraint were used to improve an initial model based on porcine pepsinogen. The present agreement factor for data from 8.0 to 2.5 angstroms (A) is 0.236. Some of the surface loops are poorly determined, and these disordered regions border a 30 A wide solvent channel. Comparison of renin with other aspartyl proteinases shows that, although the structural cores and active sites are highly conserved, surface residues, some of which are critical for specificity, vary greatly (up to 10A). Knowledge of the actual structure, as opposed to the use of models based on related enzymes, should facilitate the design of renin inhibitors.

Performing label free coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) in endoscope imaging is a challenge, with huge potential clinical benefit. To date, this goal has remained inaccessible because of the inherent coherent Raman noise that is generated in the fiber itself. By developing double-clad hollow core photonic crystal fiber, we demonstrate coherent anti-Stokes Raman scattering and stimulated Raman scattering in an "endoscope-like" scheme. Both the excitation beams and the collected CARS and SRS signals travel through the same fiber. No CARS and SRS signals are generated within the hollow core fiber even for temporally overlapping pump and Stokes beams, leading to excellent image quality. The CARS and SRS signals generated in the sample are coupled back into a high numerical aperture multimode cladding surrounding the central photonic crystal cladding. We demonstrate this scheme by imaging molecular vibrational bonds of organic crystal deposited on a glass surface.

The Saccharomyces genus (previously Saccharomyces sensu stricto) formally comprises Saccharomyces arboricola, Saccharomyces bayanus, Saccharomyces cariocanus, Saccharomyces cerevisiae, Saccharomyces kudriavzevii, Saccharomyces mikatae, Saccharomyces paradoxus and Saccharomyces pastorianus. Species-specific primer pairs that produce a single band of known and different product size have been developed for each member of the clade with the exception of S. pastorianus, which is a polyphyletic allopolyploid hybrid only found in lager breweries, and for which signature sequences could not be reliably created. Saccharomyces cariocanus is now regarded as an American variant of S. paradoxus, and accordingly a single primer pair that recognizes both species was developed. A different orthologous and essential housekeeping gene was used to detect each species, potentially avoiding competition between PCR primers and overlap between amplicons. In multiplex format, two or more different species could be identified in a single reaction; double and triple hybrids could not always be correctly identified. Forty-two unidentified yeasts from sugar cane juice fermentations were correctly identified as S. cerevisiae. A colony PCR method was developed that is rapid, robust, inexpensive and capable of automation, requires no mycological expertise on the part of the user and is thus useful for large-scale preliminary screens.

Continuous wave ultraviolet laser irradiation at = 244 nm on the +z face of undoped and MgO doped congruent lithium niobate single crystals has been observed to inhibit ferroelectric domain inversion. The inhibition occurs directly beneath the illuminated regions, in a depth greater than 100 nm during subsequent electric field poling of the crystal. Domain inhibition was confirmed by both differential domain etching and piezoresponse force microscopy. This effect allows the formation of arbitrarily shaped domains in lithium niobate and forms the basis of a high spatial resolution microstructuring approach when followed by chemical etching. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2884185͔ Domain engineering 1,2 of lithium niobate ͑LN͒ is a subject of extensive research and a simple, cheap, and robust method of fabrication of well-defined periodic domaininverted structures on submicron scales is highly desirable. Spatial domain engineering is used for many optical processes in bulk crystals and waveguides and can also allow for the creation of both freestanding 3 and surface relief structures 4 through the differential etching characteristics of the polar z faces of the crystal. If achievable on the submicron scale, surface structuring through differential etching will allow the implementation of a range of interesting applications such as tunable photonic crystals, ridge waveguide lasers, and multifunctional micromachines.Previous work has shown that ultraviolet ͑UV͒ and visible laser light can either directly invert 5 or assist the domain inversion process in LN. [6][7][8][9] In this paper, however, a different effect is presented whereby illumination of the +z face with UV light at = 244 nm ͑with photon energy greater than the LN band gap͒ inhibits domain inversion in illuminated areas during subsequent electric field poling ͑EFP͒. Of major importance, the inhibited domains are not restricted in their shape or alignment with the crystal x or y axes, hence, arbitrarily shaped domains can be formed. Some initial results of this effect and its applicability in the creation of micro/nano structures in LN are presented.A beam from a frequency-doubled Ar-ion laser was focused to a spot size of ϳ2.5 m on the +z or −z face of either an undoped congruent or 5 mol % MgO-doped LN crystal. Positioning and exposure control of the crystal was achieved by a computer-controlled, three-axis stage system coupled with a mechanical shutter.For dynamic exposures, sets of parallel lines were drawn on the z faces of the crystals along the crystallographic x or y directions by moving the stages at speeds ranging from 0.05 to 0.3 mm s −1 . For static exposures, arrays of illuminated spots with identical exposure times, ranging from a few milliseconds to a few tens of seconds, were formed. The separation between the edges of adjacent illuminated spots in the arrays varied from 0 to 6 m which permitted us to verify if any proximity effect existed such as that observed in pulsed laser direct poling 5 where the closest approa...

We report on the design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a continuous wave CO 2 laser beam in pulsed laser deposition experiments.We discuss here three potential designs for homogenising prisms and use ray-tracing modelling to compare their operation to an alternative square-tapered beam-pipe design. A square-pyramidal tetra-prism design was found to be optimal and was subjected to modelling and experimental testing to determine the influence of interference and diffraction effects on the homogeneity of the resultant intensity profile produced at the substrate surface. A heat diffusion model has been used to compare the temperature distributions produced when using various different source intensity profiles. The modelling work has revealed the importance of substrate thickness as a thermal diffuser in producing a resultant homogeneous substrate temperature distribution.

The inversion of ferroelectric domains in lithium niobate by a scanning focused ultra-violet laser beam (lambda = 244 nm) is demonstrated. The resulting domain patterns are interrogated using piezoresponse force microscopy and by chemical etching in hydrofluoric acid. Direct ultra-violet laser poling was observed in un-doped congruent, iron doped congruent and titanium in-diffused congruent lithium niobate single crystals. A model is proposed to explain the mechanism of domain inversion.

An overview is presented of recently developed light‐mediated methods for ferroelectric domain engineering of lithium niobate single crystals. These methods include light‐assisted poling, UV laser‐induced inhibition of poling, and all‐optical poling. In addition to the primary application of ferroelectric domain patterns, namely the realization of non‐linear optical devices, the ability of transferring a domain pattern into a topographical structure by domain selective etching allows also for surface structuring of lithium niobate. This intertwining between ferroelectric domain patterns and surface topography has been used to fabricate exquisite micro‐structures based on unusual domains generated purposefully by these light‐mediated methods.