A. Podlipensky

Poling-assisted bleaching of metal-doped nanocomposite glass

Thermal poling of soda-lime glass which was doped with spherical or ellipsoidal silver nanoparticles has revealed what we believe to be a phenomenon of general interest in the physics of nanocomposite materials: The field-assisted dissolution of metal nanoparticles embedded in glass. Macroscopically, this phenomenon manifested itself as poling-assisted bleaching of the glass in the sense that the glass became more (or even completely) transparent under the anode. The phenomenon is physically interpreted in terms of the ionization of metal nanoclusters followed by the removal of ions from the clusters and their drift in the depth, under the action of the extremely high electric field which is created underneath the anodic surface during poling. The underlying physical mechanism is expected to offer unique opportunities for the control of structural and optical properties of nanocomposite glasses.

Bridging visible and telecom wavelengths with a single-mode broadband photon pair source

We present a spectrally decorrelated photon pair source bridging the visible and telecom wavelength regions. Tailored design and fabrication of a solid-core photonic crystal fiber (PCF) lead to the emission of signal and idler photons into only a single spectral and spatial mode. Thus no narrowband filtering is necessary and the heralded generation of pure photon number states in ultrafast wave packets at telecom wavelengths becomes possible.

Second-harmonic generation from ellipsoidal silver nanoparticles embedded in silica glass

Second-harmonic generation of uniformly oriented, ellipsoidal silver nanoparticles in a glass matrix was observed and investigated as a function of incidence angle, light polarization, and spatial arrangement of the particles. The results can be explained by the symmetry of the spatial nanoparticle arrangement and by resonance enhancement that is due to the localized surface plasmons of the particles. Second-harmonic enhancement is observed only in sufficiently thin layers (deltakl < pi); on a sample with two separate layers, strong modulation owing to quasi-phase matching is obtained.

Pressure-controlled phase matching to third harmonic in Ar-filled hollow-core photonic crystal fiber

We report tunable third-harmonic generation (THG) in an Ar-filled hollow-core photonic crystal fiber, pumped by broadband <2 microJ, 30 fs pulses from an amplified Ti:sapphire laser system. The overall dispersion is precisely controlled by balancing the negative dielectric susceptibility of the waveguide against the positive susceptibility of the gas. We demonstrate THG to a higher-order guided mode and show that the phase-matched UV wavelength is tunable by adjusting the gas pressure.

Electric field-assisted formation of percolated silver nanolayers inside glass.

A combination of direct current (d.c.) electric field and moderately elevated temperature is applied to a glass with embedded spherical silver nanoparticles in the near surface region. The field-assisted dissolution of silver nanoparticles leads to the formation of a layer of percolated silver clusters with modified optical properties beneath the glass surface. The distance between this produced buried layer and the surface of the sample can be controlled by the magnitude of the applied voltage. The same holds for the interferential colors observable in reflection. The presented technique is easy to implement and paves a route towards the engineering of the optical properties of metal-doped nanocomposite glasses via modification of the spatial distribution of metallic inclusions.

Soliton Blueshift in Tapered Photonic Crystal Fibers

We show that solitons undergo a strong blueshift in fibers with a dispersion landscape that varies along the direction of propagation. The experiments are based on a small-core photonic crystal fiber, tapered to have a core diameter that varies continuously along its length, resulting in a zero-dispersion wavelength that moves from 731 nm to 640 nm over the transition. The central wavelength of a soliton translates over 400 nm towards a shorter wavelength. This is accompanied by strong emission of radiation into the UV and IR spectral regions. The experimental results are confirmed by numerical simulation.

Nonlinear wavelength conversion in photonic crystal fibers with three zero-dispersion points

In this theoretical study, we show that a simple endlessly single-mode photonic crystal fiber can be designed to yield, not just two, but three zero-dispersion wavelengths. The presence of a third dispersion zero creates a rich phase-matching topology, enabling enhanced control over the spectral locations of the four-wave-mixing and resonant-radiation bands emitted by solitons and short pulses. The greatly enhanced flexibility in the positioning of these bands has applications in wavelength conversion, supercontinuum generation, and pair-photon sources for quantum optics.

Generation of wavelength-dependent, periodic line pattern in metal nanoparticle-containing polymer films by femtosecond laser irradiation

Thin polymer films containing metal nanoparticles were irradiated with ultrashort, linearly polarized laser pulses. As result of irradiation, nanostructural changes occur in a type of periodically arranged, line-like areas with modified particle size and shape distribution. The periodic formation in this nanocomposite material is observed only for a small filling factor range, which can be attributed to the percolation region or nearby. Transmission (also in cross section) and scanning electron microscopy were applied to investigate the obtained structure modifications. A linear dependency between the period Λ of the line structures and the laser wavelength λ (800, 528, 400, and 266nm) used with Λ∕λ≈0.70 is assumed. The structural changes and the physical mechanism of the periodic formation are discussed.

Poling-assisted bleaching of soda-lime float glasses containing silver nanoparticles with a decreasing filling factor across the depth

The recently discovered poling-assisted bleaching of glass with embedded silver nanoparticles has renewed the interest in thermal poling as a simple, reliable, and low-cost technique for controlling locally the surface-plasmon-resonant optical properties of metal-doped nanocomposite glasses. In the present study, the emphasis is put on the influence of the volume filling factor of metallic clusters on poling-assisted bleaching. Soda-lime silicate glass samples containing spherical silver nanoparticles with a decreasing filling factor across the depth were subject to thermal poling experiments with various poling temperatures, voltages, and times. Optical extinction spectra were measured from ultraviolet to near-infrared ranges and the surface-plasmon-resonant extinction due to silver nanoparticles (around 410nm) was modeled by the Maxwell Garnett [Philos. Trans. R. Soc. London, Ser. A 203, 385 (1904); 205, 237 (1906)] effective medium theory which was adapted in order to take into account the filling fact...

Theory of Raman multipeak states in solid-core photonic crystal fibers

We provide a full theoretical understanding of the recent observations of excitation of Raman two-peak states in solid-core photonic crystal fibers. Based on a “gravity-like” potential approach we derive simple equations for the “magic” peak power ratio and the temporal separation between pulses forming these two-peak states. We develop a model to calculate the magic input power of the input pulse around which the phenomenon can be observed. We also predict the existence of exotic multipeak states that strongly violate the perturbative pulse splitting law, and we study their stability and excitation conditions.