Search results for "Physics::Optics"
showing 10 items of 1958 documents
Study of silica-based intrinsically emitting nanoparticles produced by an excimer laser
2019
International audience; We report an experimental study demonstrating the feasibility to produce both pure and Ge-doped silica nanoparticles (size ranging from tens up to hundreds of nanometers) using nanosecond pulsed KrF laser ablation of bulk glass. In particular, pure silica nanoparticles were produced using a laser pulse energy of 400 mJ on pure silica, whereas Ge-doped nanoparticles were obtained using 33 and 165 mJ per pulse on germanosilicate glass. The difference in the required energy is attributed to the Ge doping, which modifies the optical properties of the silica by facilitating energy absorption processes such as multiphoton absorption or by introducing absorbing point defect…
Fractal photon sieve
2006
A novel focusing structure with fractal properties is presented. It is a photon sieve in which the pinholes are appropriately distributed over the zones of a fractal zone plate. The focusing properties of the fractal photon sieve are analyzed. The good performance of our proposal is demonstrated experimentally with a series of images obtained under white light illumination. It is shown that compared with a conventional photon sieve, the fractal photon sieve exhibits an extended depth of field and a reduced chromatic aberration.
Spectroscopic Properties of Holmium-Aluminum-Germanium Co-doped Silica Fiber
2020
We report the basic spectroscopic properties of a home-made holmium-aluminum-germanium co-doped silica fiber, designed for laser applications. We present the ground-state and excited-state absorpti...
Optical propagation loss measurements in electro optical host-guest waveguides
2013
Thin organic waveguiding layers are applied more and more frequently as optical components in novel optoelectronic devices. For development of such devices it is important to know the optical properties of the used waveguides. One of the most important parameters is optical propagation loss in the waveguide. In this paper we present optical propagation loss measurements in planar electro optical waveguides using travelling fiber method. Using this method attenuation coefficient α at 633 nm as a function of chromophore concentration for the first two guiding modes in the slab waveguide was determined.
Guiding and reflecting light by boundary material
2003
We study effects of finite height and surrounding material on photonic crystal slabs of one- and two-dimensional photonic crystals with a pseudo-spectral method and finite difference time domain simulation methods. The band gap is shown to be strongly modified by the boundary material. As an application we suggest reflection and guiding of light by patterning the material on top/below the slab.
Crystal shape 2D modeling for transient CZ silicon crystal growth
2013
Abstract A non-stationary axisymmetric model of Czochralski silicon single crystal growth is presented. The model describes transient behavior of crystal–melt, melt–gas and crystal–gas interfaces in connection with PID-based control of crystal diameter by changing crystal pulling velocity and heater power. To calculate significant crystal shape changes, unstructured finite element mesh is used in crystal and melt together with automatic element size control. Heater temperature changes are modeled with a simplified integral model. A numerical simulation example of start cone growth is given.
The effects of ion implantation damage to photonic crystal optomechanical resonators in silicon
2021
Abstract Optomechanical resonators were fabricated on a silicon-on-insulator substrate that had been implanted with phosphorus donors. The resonators’ mechanical and optical properties were then measured (at 6 K and room temperature) before and after the substrate was annealed. All measured resonators survived the annealing and their mechanical linewidths decreased while their optical and mechanical frequencies increased. This is consistent with crystal lattice damage from the ion implantation causing the optical and mechanical properties to degrade and then subsequently being repaired by the annealing. We explain these effects qualitatively with changes in the silicon crystal lattice struc…
Phonon-plasmon coupling in Si doped GaN nanowires
2016
Abstract The vibrational properties of silicon doped GaN nanowires with diameters comprised between 40 and 100 nm are studied by Raman spectroscopy through excitation with two different wavelengths: 532 and 405 nm. Excitation at 532 nm does not allow the observation of the coupled phonon–plasmon upper mode for the intentionally doped samples. Yet, excitation at 405 nm results in the appearance of a narrow peak at frequencies close to that of the uncoupled A 1 (LO) mode for all samples. This behavior points to phonon–plasmon scattering mediated by large phonon wave-vector in these thin and highly doped nanowires.
On-chip periodic arrays of optical traps based on the superposition of guided modes in silicon waveguides
2019
Since the pioneering work of Kawata and Tani [1], photonic waveguides have long been regarded as efficient optical conveyor belts for potential lab-on-a-chip applications. Indeed, near-field optical forces arising at the surface of such waveguides lead to efficient on-chip guided propulsion of micro- and even nanoparticles [2], as well as cells and bacteria in liquid solutions [3]. However, achieving stable and precisely controlled optical trapping of particles at the surface of a waveguide has been made possible only recently, and even then, it still requires complex photonic electro-optic tools to produce and handle on-chip standing waves [4].
Silicon resonator sensors: interrogation techniques and characteristics
1988
Interferometric and noninterferometric optical-fibre sensing systems for resonator vibrations are described. The quality factor variation with pressure, the temperature dependence of resonant frequency and the acceleration sensitivity are given for a double-ended tuning-fork based acceleratometer.