Trigonal Na3Li(SeO4)2·6H2O crystal – a novel SRS‐active material with high Raman gain coefficient

We discovered and characterized the χ ⁽³⁾‐active Na₃Li(SeO₄)₂·6H₂O crystal with considerably high Raman gain coefficients for laser physics and nonlinear optics. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

     

Theory of singular vortex solutions of the nonlinear Schrödinger equation

We present a systematic study of singular vortex solutions of the critical and supercritical two-dimensional nonlinear Schrödinger equation. In particular, we study the critical power for collapse and the asymptotic blowup profile of singular vortices.     

<Emphasis Type="Italic">Z</Emphasis>-scan technique through beam radius measurements

A modification to the well-known z-scan technique for measuring optical non-linearities is introduced. It is based on directly measuring the beam radius in the far field instead of the transmittance of the irradiance through an aperture, as in the original version. It has the advantage of being insensitive to beam pointing instability and is almost insensitive to power fluctuations. Furthermore, the calculations required for the determination of the non-linear parameters are simplified. For demonstrating the advantages of the modified method, beam radius and transmittance measurements were simultaneously taken in the standard non-linear optical material CS₂. Separate fittings of these measurements gave almost the same values for the non-linearities, quite similar to those in the literature. A common fitting has been applied to both sets of measurements, enhancing the accuracy of the method. Received: 8 July 2002 / Revised version: 18 October 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +30-2610/997470, E-mail: gianetas@physics.upatras.gr     

Supercontinuum extending from > 1000 to 250 nm, generated by focusing ten-fs laser pulses at 805 nm into Ar

Ten femtosecond pulses at 805 nm with energy up to 1 mJ were produced by self-phase modulation of 45-fs pulses in Ar at atmospheric pressure and subsequent compression by chirped mirrors. Focusing part of this radiation again into Ar at atmospheric pressure generates a single filament with broadband emission covering the range from > 1000 to 250 nm. This range extends farther into the UV than previously observed with such low energies, overlapping even the region of the third harmonic. Only a small fraction of the power is contained outside the central spot. Using a simple prism compressor, pulses were obtained with durations of 70 fs and energies of 700 nJ in the range 270–290 nm.This revised version was published online in March 2005. The last name of the corresponding author W. Fuß was corrected.     

Variable-coefficient higher-order nonlinear Schrödinger model in optical fibers: Variable-coefficient bilinear form,Bäcklund transformation,brightons and symbolic computation

Symbolically investigated in this Letter is a variable-coefficient higher-order nonlinear Schrödinger (vcHNLS) model for ultrafast signal-routing, fiber laser systems and optical communication systems with distributed dispersion and nonlinearity management. Of physical and optical interests, with bilinear method extend, the vcHNLS model is transformed into a variable-coefficient bilinear form, and then an auto-Bäcklund transformation is constructed. Constraints on coefficient functions are analyzed. Potentially observable with future optical-fiber experiments, variable-coefficient brightons are illustrated. Relevant properties and features are discussed as well. Bäcklund transformation and other results of this Letter will be of certain value to the studies on inhomogeneous fiber media, core of dispersion-managed brightons, fiber amplifiers, laser systems and optical communication links with distributed dispersion and nonlinearity management.     

Wave mixing in nominally undoped Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> at high light intensities

The intensity dependence of the photorefractive response of Sn₂P₂S₆ is studied for the Kr⁺-laser wavelength of 647 nm and pump-beam intensities of up to 10 W/cm². A considerable enhancement of the two-beam coupling gain factor with increasing intensity at a grating spacing of ≃1 μm is attributed to a light-induced increase of the effective trap density. The large gain reached at high intensities is applied for the build up of a double phase conjugate mirror with a sub-millisecond switch-on time.     

Azimuthal modulational instability of vortices in the nonlinear Schrödinger equation

We study the azimuthal modulational instability of vortices with different topological charges, in the focusing two-dimensional nonlinear Schrödinger (NLS) equation. The method of studying the stability relies on freezing the radial direction in the Lagrangian functional of the NLS in order to form a quasi-one-dimensional azimuthal equation of motion, and then applying a stability analysis in Fourier space of the azimuthal modes. We formulate predictions of growth rates of individual modes and find that vortices are unstable below a critical azimuthal wave number. Steady-state vortex solutions are found by first using a variational approach to obtain an asymptotic analytical ansatz, and then using it as an initial condition to a numerical optimization routine. The stability analysis predictions are corroborated by direct numerical simulations of the NLS. We briefly show how to extend the method to encompass nonlocal nonlinearities that tend to stabilize such solutions.     

Nonautonomous “rogons” in the inhomogeneous nonlinear Schrödinger equation with variable coefficients

The analytical nonautonomous rogons are reported for the inhomogeneous nonlinear Schrödinger equation with variable coefficients in terms of rational-like functions by using the similarity transformation and direct ansatz. These obtained solutions can be used to describe the possible formation mechanisms for optical, oceanic, and matter rogue wave phenomenon in optical fibres, the deep ocean, and Bose-Einstein condensates, respectively. Moreover, the snake propagation traces and the fascinating interactions of two nonautonomous rogons are generated for the chosen different parameters. The obtained nonautonomous rogons may excite the possibility of relative experiments and potential applications for the rogue wave phenomenon in the field of nonlinear science.     

Exact spatial soliton solution for nonlinear Schrödinger equation with a type of transverse nonperiodic modulation

In this paper, we analyze (2 + 1)D nonlinear Schrödinger (NLS) equation based on a type of nonperiodic modulation of linear refractive index in the transverse direction. We obtain an exact solution in explicit form for the (2 + 1)D nonlinear Schrödinger (NLS) equation with the nonperiodic modulation. Finally, the stability of the solution is discussed numerically, and the results reveal that the solution is stable to the finite initial perturbations.     

Femtosecond laser pulse filamentation versus optical breakdown in H<Subscript>2</Subscript>O

The competition between femtosecond laser pulse induced optical breakdown and femtosecond laser pulse filamentation in condensed matter is studied both experimentally and numerically using water as an example. The coexistence of filamentation and breakdown is observed under tight focusing conditions. The development of the filamentation process from the creation of a single filament to the formation of many filaments at higher pulse energy is characterized systematically. In addition, strong deflection and modulation of the supercontinuum is observed. They manifest themselves at the beginning of the filamentation process, near the highly disordered plasma created by optical breakdown at the geometrical focus. Received: 9 July 2002 / Revised version: 15 November 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +1-418/6562-623, E-mail: wliu@phy.ulaval.ca     

Rapid and simple detection of sodium thiocyanate in milk using surface‐enhanced Raman spectroscopy based on silver aggregates

Surface‐enhanced Raman spectroscopy (SERS) was used for rapid detection of sodium thiocyanate in milk employing silver aggregates as active substrate. Silver nanoparticles were induced to silver aggregates by trichloroacetic acid (TCA). The limit of detection (LOD) for sodium thiocyanate was 10⁻² µg ml⁻¹ in water with an analytical enhancement factor of 5.4 × 10⁶. The silver aggregates represent good reproducibility and stability. Good linear relationship was obtained for sodium thiocyanate in milk at concentration ranges from 0.1 to 10 µg ml⁻¹ (R² = 0.995). Using TCA as protein precipitator, silver colloid would aggregate spontaneously when mixing with samples during SERS measurement without the need of additional aggregating agent. The simple pretreatment procedures and analytical methods are less time consuming (<10 min) and environmentally friendly, making the proposed method much practical for in situ detection of sodium thiocyanate in market milk. Copyright © 2014 John Wiley & Sons, Ltd.     

Efficient multi-frequency generation of ultrashort light pulses using stimulated Raman scattering and optical parametric amplification

Optical parametric amplification of multi-frequency seed pulses generated in a mixture of compressed hydrogen and methane by stimulated Raman scattering of 1 ps, 1 kHz laser pulses at 395.8 nm has been studied. Efficient generation of spectrally narrow ultrashort pulses with a spatial distribution close to the Gaussian profile of the pump beam was obtained in the visible and near infrared ranges.     

28.4 W 266 nm ultraviolet-beam generation by fourth-harmonic generation of an all-solid-state laser

In this paper, 28.4 W 266 nm ultraviolet-beam generation by fourth-harmonic generation of an all-solid-state laser using a CsLiB₆O₁₀ crystal was reported. A conversion efficiency of 24.7% was obtained.     

Optical modes in a nonlinear double-channel waveguide

We analytically address different types of optical modes in a coupler composed by two nonlinear optical waveguides. It is shown that the coupler not only supports symmetry-preserving modes but also symmetry-breaking modes. In addition, the properties on the existence and bifurcation of those modes are analyzed in detail.     

Effects of dark soliton crystal temperature on the self-deflection of bright soliton in a biased serial photovoltaic photorefractive crystal circuit

Based on the theory of one-dimensional separate soliton pairs formed in a serial photovoltaic photorefractive crystal circuit, the effects of the dark soliton crystal temperature on the self-deflection of the bright one in a bright-dark soliton pair are investigated. The numerical results indicate that the spatial shift of the bright soliton can experience obvious increase in their self-deflection with the increase of the temperature of the dark soliton. The self-bending process is further studied using perturbation techniques and the results are found to be good agreement with that obtained by numerical method.     

Simulation of Femtosecond Pulse Propagation through Hollow Fibre Filled with Noble Gases of Gradient Temperature

We propose a novel technique for generating intense few to mono-cycle femtosecond pulses. The simulation demonstrate that for the temperature difference of 300K, the spectrum of the output pulses is increased by 67% and the transform limited pulse width is reduced almost by half, compared with those obtained with hollow fibres in uniform temperature.     

Defect vector gap solitons in photonic lattices

The existence and general properties of different kinds of defect vector gap solitons in one dimensional optically induced photonic defect lattice with focusing saturable nonlinearity in photorefractive crystal are analyzed. The defect is well localized in a single site with two existence forms, namely repulsive and attractive defect. Propagation constants of two beams that compose defect vector gap solitons could be from same gap or from different gaps. We show that some kinds of unstable scalar defect gap solitons could be stabilized by their corresponding vector cases.     

Self-compression and controllable guidance of multi-millijoule femtosecond laser pulses

Self-compression of multi-millijoule femtosecond laser pulses and dramatic increase of the peak intensity are found in pressurized helium and neon within a range of intensity in which the ionization modification of the material parameters by the pulse is negligible. The pulse propagation is studied by the (3 + 1)-dimensional nonlinear Schrödinger equation including basic lowest order optical processes - diffraction, second order of dispersion, and third order of nonlinearity. Smooth and well controllable pulse propagation dynamics is found. Construction of compressed pulses of controllable parameters at given space target point by a proper chose of the pulse energy and/or gas pressure is predicted.     

Temporal behavior of dark spatial solitons in closed-circuit photovoltaic media

We show that the time-dependent nonlinear wave equation in closed-circuit photovoltaic media can exhibit quasi-steady-state and steady-state spatial solitons. We demonstrate that the formation time of open-circuit quasi-steady-state and open-circuit steady-state dark solitons decreases with an increase in the intensity ratio of the soliton, which is the ratio between the soliton peak intensity and the dark irradiance. We find that for the time-dependent nonlinear wave equation that exhibits only an open-circuit steady-state dark soliton, changing the electric current density J₀ does not generate quasi-steady-state dark solitons and affects the formation time of steady-state dark solitons and that for the time-dependent nonlinear wave equation that exhibits an open-circuit quasi-steady-state dark soliton, changing J₀ gives rise to three different time evolution regimes of the full width half maximum of the soliton’s intensity. The first regime shows that the formation time of steady-state dark solitons increases with J₀ whereas the formation time of quasi-steady-state dark solitons is independent of J₀. The second regime shows that the formation time of steady-state dark solitons decreases with an increases in J₀ and the formation time of quasi-steady-state dark solitons increases with J₀. The third regime shows that changing J₀ enables only steady-state dark solitons in the time-dependent nonlinear wave equation, of which the formation time increases with J₀.     

41 mW high average power picosecond 177.3 nm laser by second-harmonic generation in KBBF

We report on the generation of high average power, high repetition rate, and picosecond (ps) deep-ultraviolet (DUV) 177.3 nm laser. The DUV laser is produced by second-harmonic generation of a frequency-tripled mode-locked Nd: YVO₄ laser (<15 ps, 80 MHz) with KBBF nonlinear crystal. The influence of different fundamental beam diameters on DUV output power and KBBF-SHG conversion efficiency are investigated. Under the 355 nm pump power of 7.5 W with beam diameter of 145 μm, 41 mW DUV output at 177.3 nm is obtained. To our knowledge, this is the highest average power for the 177.3 nm laser. Our results provide a power scaling by three times with respect to previous best works.