Search results for "Physics::Optics"
showing 10 items of 1958 documents
Sensitive laser spectroscopy on trapped barium ions by quenching with hydrogen
1983
The sensitivity of laser spectroscopy on barium ions stored in a radio frequency quadrupole trap was drastically increased by using hydrogen for quenching the optically pumped metastable states. The attained fluorescence intensity per ion permits the detection of single ions. The method will be applied to environmental studies on actinides.
Dynamic Characterization of Upconversion in Highly Er-Doped Silica Photonic Crystal Fibers
2012
Measurements of time evolution of amplified spontaneous emission for square-wave modulated pump were made on a highly erbium-doped silica photonic crystal fiber and fitted to theoretical results calculated using different formalisms to describe the ${\rm Er}^{3+}$ -ion migration-assisted co-operative upconversion mechanism in the population densities rate equations. The determined characterization parameters are the constant homogeneous upconversion coefficient, 3.0 $\times 10^{-24}~{\rm m}^{3}/{\rm s}$ , the critical radii for upconversion and migration, 10.5 and 14A, respectively, and the rate of clustered ions, 14%. These parameters are analysed and compared to those obtained with contin…
Particle size-related limitations of persistent phosphors based on the doped Y3Al2Ga3O12 system
2021
AbstractCo-doped Ce3+, Cr3+ and Pr3+ yttrium–aluminium–gallium garnet powders of various sizes were obtained by co-precipitation method. The microstructure and morphology were investigated by XRPD, TEM and gas porosimetry. The luminescence properties were studied by excitation and emission spectra, quantum yield and decay times. Thermoluminescence measurements were performed to evaluate the activation energy, traps redistribution and frequency factor. Limitation in the energy transfer between dopant ions in the small particles, traps depth and surface defects were considered and investigated as responsible for the quenching of persistent luminescence. The phosphors annealed at 1100 °C show …
A new method for detemining the Angstrom turbidity coefficient from broad-band filter measurements.
2000
In this work, a new method for determining Ångström turbidity coefficients is presented. This method is based on broadband filter irradiance measurements. By combining measurements obtained with different filters it is possible to obtain a single value of the turbidity coefficient representative of the whole measurement range of the pyrheliometer. The results provided by this new method are compared with the original Ångström method and turbidity coefficient values derived by spectroradiometric measurements. The results reproduce the actual values, as measured by a spectroradiometer, better than the previous best correlation did, thus demonstrating the advantage of analyzing the optical thi…
The energy transfer to the luminescence centers in PbWO4
1998
Abstract The luminescence spectra, rise and decay kinetics and the yield of luminescence in undoped PbWO 4 crystals were studied after pulsed electron beam irradiation. The luminescence intensity rise observed after irradiation pulse showed two mechanisms—excitonic relaxation and electron–hole recombination—were involved in the formation of the excited states of the blue luminescence centers. It is proposed that the excited states of WO 3 and WO 2− 4 luminescence centers were formed from some intermediate metastable state.
Development of accelerator mass spectrometry assisted by isotope-selective laser photodetachment for monitoring 129I
2013
Abstract A prototype system was developed to investigate an isotope-selective laser photodetachment technique for a 129 I accelerator mass spectrometer. A pulsed ion source for negative iodine ions (I − ) that employed laser ablation proved to be suitable for isotope-selective laser photodetachment. Laser photodetachment of pulsed negative iodine ions was estimated to have an efficiency of about 81% based on a model calculation for the prototype system with a tunable pulsed Ti:sapphire laser.
Dyadic Green's function for the electrically biased graphene-based multilayered spherical structures
2020
Abstract Dyadic Green's function for a multilayered spherical structure with alternating graphene-dielectric shells is extracted in this paper. To this end, the unknown expansion coefficients of the scattering superposition method are obtained by considering graphene local surface currents at the interface of two adjacent layers. To validate the formulas, the procedure of Mie scattering analysis employing our formulas is clarified and the extinction efficiencies of various graphene-based nanoparticles are computed. The possibility of using the proposed structure in the design of multi-band optical absorbers is discussed in detail. Moreover, a closed-form formula for obtaining the Purcell fa…
Spectroscopy of an optical excited Ga doped SiO2 surface
2007
Abstract We present the first spectroscopical analysis of the Ga/SiO2 surface interaction in hot environment. This interaction gives rise to inclusions of Ga atoms inside the silica matrix that produce structural changes and modify the SiO2 optical characteristics. This paper discusses both the time- and the frequency-resolved spectra of the fluorescence emission following UV pulsed laser excitation of the so “doped” silica in the range 15,000–28,000 cm−1. The investigation is completed by the electron paramagnetic resonance (EPR) spectra of two high-purity synthetic silica samples of commercial origin after thermal treatment in presence and in absence of a Ga atmosphere.
Photoemission time-of-flight spectromicroscopy of Ag nanoparticle films on Si(111)
2004
Abstract Time-of-flight photoemission electron microscopy was used to measure spatially resolved energy distribution curves of electrons emitted from Ag nanoparticle films with different mass thicknesses. Two-photon photoemission (2PPE) was induced by femtosecond laser pulse excitation with 3.1 eV photon energy and 200 fs pulse width. Regions of Ag nanoparticles with different average sizes and one region with a continuous 100 nm thick Ag film were deposited as a stepped wedge on a Si(1 1 1) substrate. Upon laser excitation the nanoparticle films exhibit a very high electron emission yield in the images, whereas the uncovered Si surface and the continuous Ag film are dark. The time-of-fligh…
Multiphoton photoemission electron microscopy using femtosecond laser radiation
2002
Abstract The interaction of intense, pulsed laser radiation with surfaces results in non-linear optical effects that are responsible for emission of electrons even if the photon energies are below the work function. In the present study, photoelectrons have been excited by means of femtosecond laser pulses from a frequency doubled Ti:sapphire laser with a photon energy of 3.1 eV. The spatial distribution of the photo emitted electrons was imaged using a photoemission electron microscope. All samples exhibit centres of enhanced second or higher order photoemission yield, so called ‘hot spots’. These ‘hot spots’ were preferentially excited with s-polarised light. This behaviour may be explain…