Search results for "Physics::Optics"
showing 10 items of 1958 documents
Spatio-temporal structures of laser-induced anisotropy
1999
We report new observations of optical spatio-temporal structures formed in terbium gallium garnet when it is excited at resonance by a strong laser beam. We also present a theoretical description of this pattern formation, which accounts well for our observations. We finally discuss useful applications of both time and power dependence of these structures.
Transparent conductive oxide photonic crystals on textured substrates
2011
Three-dimensional ZnO:Al photonic crystals were fabricated by atomic layer deposition on highly textured substrates. It turns out that these inverted opals consist of a thin intermediate disordered layer close to the textured substrate followed by a highly-ordered photonic crystal layer. The photonic crystals themselves exhibit comparable optical properties to those on planar substrates.
Tapering photonic crystal fibres for supercontinuum generation with nanosecond pulses at 532nm
2008
Experimental results on supercontinuum generation in photonic crystal fibre tapers using pump pulses of 7 ns duration at 532 nm are presented. Photonic crystal fibre tapers with the first wavelength of zero dispersion around 532 nm were fabricated. The generation of supercontinuum was investigated in normal and anomalous dispersion regimes. Supercontinuum spectra spanning more than 400 nm in the visible region are reported.
Cantor-like fractal photonic crystal waveguides
2005
Abstract We propose a new class of one-dimensional (1D) photonic waveguides: the fractal photonic crystal waveguides (FPCWs). These structures are photonic crystal waveguides (PCWs) etched with fratal distribution of grooves such as Cantor bars. The transmission properties of the FPCWs are investigated and compared with those of the conventional 1D PCWs. It is shown that the FPCW transmission spectrum has self-similarity properties associated with the fractal distribution of grooves. Furthermore, FPCWs exhibit sharp localized transmissions peaks that are approximately equidistant inside the photonic band gap.
Actively mode-locked fiber laser with an acousto-optic in-fiber superlattice modulator
2009
All-fiber lasers permit the development of efficient, robust and compact coherent light sources. However, all-fiber active mode-locking is a challenging objective and very few all-fiber techniques have been published [1–3]. The development of a low-insertion-loss acoustically-induced superlattice modulator that works in the MHz range has demonstrated its suitability to perform active mode-locking of an all-fiber laser. While travelling extensional acoustic waves launched along a fiber Bragg grating (FBG) produce stationary side bands and a frequency shift [4,5], we found that the excitation of a standing extensional acoustic wave should produce no frequency shift, but the amplitude modulati…
Photoemission Electron Microscopy as a tool for the investigation of optical near fields
2005
Photoemission electron microscopy was used to image the electrons photoemitted from specially tailored Ag nanoparticles deposited on a Si substrate (with its native oxide SiO$_{x}$). Photoemission was induced by illumination with a Hg UV-lamp (photon energy cutoff $\hbar\omega_{UV}=5.0$ eV, wavelength $\lambda_{UV}=250$ nm) and with a Ti:Sapphire femtosecond laser ($\hbar\omega_{l}=3.1$ eV, $\lambda_{l}=400$ nm, pulse width below 200 fs), respectively. While homogeneous photoelectron emission from the metal is observed upon illumination at energies above the silver plasmon frequency, at lower photon energies the emission is localized at tips of the structure. This is interpreted as a signat…
Femtosecond time-resolved photoemission electron microscopy operated at sample illumination from the rear side
2019
We present an advanced experimental setup for time-resolved photoemission electron microscopy (PEEM) with sub-20 fs resolution, which allows for normal incidence and highly local sample excitation with ultrashort laser pulses. The scheme makes use of a sample rear side illumination geometry that enables us to confine the sample illumination spot to a diameter as small as 6 μm. We demonstrate an operation mode in which the spatiotemporal dynamics following a highly local excitation of the sample is globally probed with a laser pulse illuminating the sample from the front side. Furthermore, we show that the scheme can also be operated in a time-resolved normal incidence two-photon PEEM mode w…
Cylindrical Cell-Based Refractometers to Analyse Biomedical Liquids
2015
Compact device of high sensitivity for measurement of the refractive indices of both stationary and flowing liquids has been developed. This device can be used to analyse a variety of biomedical liquids: urine, serum protein. The refractive index (RI) is determined by measuring the deviation of a laser beam passing through a cylindrical cell containing the test liquid. In order to significantly improve the resolution and stability of RI measurements, the repeated reflections and refractions of the light beam travelling through the cylindrical cell are employed.
Imaging of photonic nanopatterns by scanning near-field optical microscopy
2002
We define photonic nanopatterns of a sample as images recorded by scanning near-field optical microscopy with a locally excited electric dipole as a probe. This photonic nanopattern can be calculated by use of the Green’s dyadic technique. Here, we show that scanning near-field optical microscopy images of well-defined gold triangles taken with the tetrahedral tip as a probe show a close similarity to the photonic nanopattern of this nanostructure with an electric dipole at a distance of 15 nm to the sample and tilted 45° with respect to the scanning plane.
Narrowing the Plasmonic Sensitivity Distribution by Considering the Individual Size of Gold Nanorods
2018
The plasmonic nanoparticle sensitivity, sensing volume, and the signal-to-noise ratio are strongly dependent on the nanoparticle dimensions. It is difficult to chemically produce or purify nanoparticles with a size variation of less than 10%. This size variation induces a systematic error in sensing experiments that can be reduced when the exact size of each individual nanoparticle is known. In this work, we show how the size of gold nanorods can be estimated directly from the optical spectra of single nanoparticles by using the increase of radiation damping with the nanoparticle size. We verify our approach by comparing these spectrally estimated sizes with the precise sizes of exactly the…