Theory of plasmon-enhanced high-harmonic generation in the vicinity of metal nanostructures in noble gases

We present a semiclassical model for plasmon-enhanced high-harmonic generation (HHG) in the vicinity of metal nanostructures. We show that both the inhomogeneity of the enhanced local fields and electron absorption by the metal surface play an important role in the HHG process and lead to the generation of even harmonics and to a significantly increased cutoff. For the examples of silver-coated nanocones and bowtie antennas we predict that the required intensity reduces by up to three orders of magnitudes and the HHG cutoff increases by more than a factor of two. The study of the enhanced high-harmonic generation is connected with a finite-element simulation of the electric field enhancement due to the excitation of the plasmonic modes.Comment: 4 figure

Multistability at arbitrary low optical intensities in a metallo-dielectric layered structure

We show that a nonlinear metallo-dielectric layered slab of subwavelength thickness and very small average dielectric permittivity displays optical multistable behavior at arbitrary low optical intensities. This is due to the fact that, in the presence of the small linear permittivity, one of the multiple electromagnetic slab states exists no matter how small is the transmitted optical intensity. We prove that multiple states at ultra-low optical intensities can be reached only by simultaneously operating on the incident optical intensity and incidence angle. By performing full wave simulations, we prove that the predicted phenomenology is feasible and very robust.Comment: 4 pages, 4 figure

All-optical attoclock: accessing exahertz dynamics of optical tunnelling through terahertz emission

The debate regarding attosecond dynamics of optical tunneling has so far been focused on time delays associated with electron motion through the potential barrier created by intense ionizing laser fields and the atomic core. Compelling theoretical and experimental arguments have been put forward to advocate the polar opposite views, confirming or refuting the presence of tunnelling time delays. Yet, such delay, whether present or ot, is but a single quantity characterizing the tunnelling wavepacket; the underlying dynamics are richer. Here we propose to complement photo-electron detection with detecting light, focusing on the so-called Brunel adiation -- the near-instantaneous nonlinear optical response triggered by the tunnelling event. Using the combination of single-color and two-color driving fields, we determine not only the ionization delays, but also the re-shaping of the tunnelling wavepacket as it emerges from the classically forbidden region. Our work introduces a new type of attoclock for optical tunnelling, one that is based on measuring light rather than photo-electrons. All-optical detection paves the way to time-resolving multiphoton transitions across bandgaps in solids, on the attosecond time-scale

Deeply-trapped molecules in self-nanostructured gas-phase material

Since the advent of atom laser-cooling, trapping or cooling natural molecules has been a long standing and challenging goal. Here, we demonstrate a method for laser-trapping molecules that is radically novel in its configuration, in its underlined physical dynamics and in its outcomes. It is based on self-optically spatially-nanostructured high pressure molecular hydrogen confined in hollow-core photonic-crystal-fibre. An accelerating molecular-lattice is formed by a periodic potential associated with Raman saturation except for a 1-dimentional array of nanometer wide and strongly-localizing sections. In these sections, molecules with a speed of as large as 1800 m/s are trapped, and stimulated Raman scattering in the Lamb-Dicke regime occurs to generate high power forward and backward-Stokes continuous-wave laser with sideband-resolved sub-Doppler emission spectrum. The spectrum exhibits a central line with a sub-recoil linewidth of as low as 14 kHz, more than 5 orders-of-magnitude narrower than in conventional Raman scattering, and sidebands comprising Mollow triplet, molecular motional-sidebands and four-wave-mixing.Comment: 28 pages 1-12 for main manuscript 13-28 for Methodes and appendices 4 figures for Main manuscript 12 figures for the Methods par

Raman gas self-organizing into deep nano-trap lattice

Trapping or cooling molecules has rallied a long-standing effort for its impact in exploring new frontiers in physics and in finding new phase of matter for quantum technologies. Here we demonstrate a system for light-trapping molecules and stimulated Raman scattering based on optically self-nanostructured molecular hydrogen in hollow-core photonic crystal fibre. A lattice is formed by a periodic and ultra-deep potential caused by a spatially modulated Raman saturation, where Raman-active molecules are strongly localized in a one-dimensional array of nanometre-wide sections. Only these trapped molecules participate in stimulated Raman scattering, generating high-power forward and backward Stokes continuous-wave laser radiation in the Lamb-Dicke regime with sub-Doppler emission spectrum. The spectrum exhibits a central line with a sub-recoil linewidth as low as ∼14 kHz, more than five orders of magnitude narrower than conventional-Raman pressure-broadened linewidth, and sidebands comprising Mollow triplet, motional sidebands and four-wave mixing

High-power supercontinuum generation in dielectric-coated metallic hollow waveguides

In this Letter we theoretically study a novel approach for soliton-induced supercontinuum generation based on the application of metallic dielectric-coated hollow waveguides. Low loss of such waveguides permits the use of smaller diameters with enhanced dispersion control and enables the generation of two-octave-broad spectra with unprecedentedly high spectral peak power densities up to five orders of magnitude larger than in standard PCFs with high coherence. We also predict that high-power supercontinua in the vacuum ultraviolet can be generated in such waveguides.Comment: 5 pages, 3 figure

Modulation control and spectral shaping of optical fiber supercontinuum generation in the picosecond regime

Numerical simulations are used to study how fiber supercontinuum generation seeded by picosecond pulses can be actively controlled through the use of input pulse modulation. By carrying out multiple simulations in the presence of noise, we show how tailored supercontinuum Spectra with increased bandwidth and improved stability can be generated using an input envelope modulation of appropriate frequency and depth. The results are discussed in terms of the non-linear propagation dynamics and pump depletion.Comment: Aspects of this work were presented in Paper ThJ2 at OECC/ACOFT 2008, Sydney Australia 7-10 July (2008). Journal paper submitted for publication 30 July 200

Bright broadband coherent fiber sources emitting strongly blue-shifted resonant dispersive wave pulses

We predict and realize the targeted wavelength conversion from the 1550-nm band of a fs Er:fiber laser to an isolated band inside 370-850 nm, corresponding to a blue-shift of 700-1180 nm. The conversion utilizes resonant dispersive wave generation in widely available optical fibers with good efficiency (~7%). The converted band has a large pulse energy (~1 nJ), high spectral brightness (~1 mW/nm), and broad Gaussian-like spectrum compressible to clean transform-limited ~17 fs pulses. The corresponding coherent fiber sources open up portable applications of optical parametric oscillators and dual-output synchronized ultrafast lasers

Solitons in one-dimensional photonic crystals

We report results of a systematic analysis of spatial solitons in the model of 1D photonic crystals, built as a periodic lattice of waveguiding channels, of width D, separated by empty channels of width L-D. The system is characterized by its structural "duty cycle", DC = D/L. In the case of the self-defocusing (SDF) intrinsic nonlinearity in the channels, one can predict new effects caused by competition between the linear trapping potential and the effective nonlinear repulsive one. Several species of solitons are found in the first two finite bandgaps of the SDF model, as well as a family of fundamental solitons in the semi-infinite gap of the system with the self-focusing nonlinearity. At moderate values of DC (such as 0.50), both fundamental and higher-order solitons populating the second bandgap of the SDF model suffer destabilization with the increase of the total power. Passing the destabilization point, the solitons assume a flat-top shape, while the shape of unstable solitons gets inverted, with local maxima appearing in empty layers. In the model with narrow channels (around DC =0.25), fundamental and higher-order solitons exist only in the first finite bandgap, where they are stable, despite the fact that they also feature the inverted shape