Search results for " laser"
showing 10 items of 1455 documents
Nd:YAG laser induced E′ centers probed by in situ absorption measurements
2005
We investigated various types of commercial silica irradiated with a pulsed Nd:YAG laser radiation (4.66 eV), with exposure time ranging up to 10000 s. Transient E' centers were probed in situ by measuring the amplitude of the optical absorption band at 5.8 eV (due to E' centers) both during and after irradiation. The laser-induced absorption is observed only in natural samples, whereas the synthetic materials exhibit high toughness to radiation effect. The reported results evidence that the kinetics of E' centers is influenced by their reaction with diffusing molecular hydrogen H2 made available by dimerization of radiolytic H0.
Bleaching of optical activity induced by UV Laser exposure in natural silica
2004
We report experimental data on two types of natural silica, differing for their OH content, irradiated with UV photons (4.66 eV) from a pulsed Nd:YAG laser. Irradiation induces a reduction of the absorption band at 5.12eV and of the associated emissions at 3.14eV and 4.28eV, ascribed to twofold coordinated Ge (=Ge'') centers pre-existing in our samples. The bleaching is mainly due to the post-irradiation conversion of =Ge'' into the paramagnetic H(II) center via trapping of a H atom. Comparison with literature data points out the peculiarities of silica with a low Ge concentration as regards UV induced transformations.
Optical absorption induced by UV laser radiation in Ge-doped amorphous silica probed by in situ spectroscopy
2007
We studied the optical absorption induced by 4.7eV pulsed laser radiation on Ge-doped a-SiO2 synthesized by a sol-gel technique. The absorption spectra in the ultraviolet spectral range were measured during and after the end of irradiation with an in situ technique, evidencing the growth of an absorption signal whose profile is characterized by two main peaks near 4.5eV and 5.7eV and whose shape depends on time. Electron spin resonance measurements performed ex situ a few hours after the end of exposure permit to complete the information acquired by optical absorption by detection of the paramagnetic Ge(1) and Ge-E' centers laser-induced in the samples.
Transport Properties of Co2(Mn, Fe)Si Thin Films
2013
Thin Heusler films with the composition Co2Mn1−x Fe x Si were grown by both sputter and pulsed laser deposition. The samples show a high degree of structural order and very good magnetic properties. The availability of thin film samples on dielectric substrates allowed the systematic investigation of their electronic properties by transport experiments. The normal Hall effect shows a transition from a hole-like charge transport in Co2MnSi to an electron-like transport in Co2FeSi. This is in agreement with calculations, which predict that the substitution of Mn by Fe leads to a band filling and a shift of the Fermi energy. Furthermore, the behavior of the anomalous Hall effect was studied. I…
<title>Collisional and thermal ionization of sodium Rydberg atoms in single and crossed atomic beams</title>
2006
The results of the experimental and theoretical study on associative ionization of laser excited Na Rydberg atoms in collisions with ground-state atoms and on thermal ionization by blackbody radiation in single and crossed effusive atomic beams are reported and discussed.
Luminescence center excited state absorption in tungstates
2001
The excited state absorption of intrinsic luminescence center (self-trapped exciton) in tungstates (CaWO4, ZnWO4, PbWO4 and CdWO4) was studied. The transient absorption and luminescence spectra, decay kinetics and lifetime dependencies on temperature have been measured. The model of self-trapped exciton and nature of observed absorption bands were discussed.
Formation, Detection and Trapping of Photoassociated Ultracold KRb Molecules
2005
Ultracold ground-state KRb molecules are formed by photoassociation and detected by resonant two-photon ionization. We have assigned both the photoassociation spectrum and the detection laser spectrum, and we have demonstrated magnetic trapping of triplet KRb
Entanglement control in hybrid optomechanical systems
2012
We demonstrate the control of entanglement in a hybrid optomechanical system comprising an optical cavity with a mechanical end-mirror and an intracavity Bose-Einstein condensate (BEC). Pulsed laser light (tuned within realistic experimental conditions) is shown to induce an almost sixfold increase of the atom-mirror entanglement and to be responsible for interesting dynamics between such mesoscopic systems. In order to assess the advantages offered by the proposed control technique, we compare the time-dependent dynamics of the system under constant pumping with the evolution due to the modulated laser light.
Approaching the limits of multiple scattering decorrelation: 3D light-scattering apparatus utilising semiconductor lasers
2007
Light scattering as a function of scattering angle can be regarded as a standard method to investigate the dynamics of dilute colloidal suspensions. Concentrated suspensions, which are of interest if interactions between the particles are to be investigated, usually show strong multiple scattering. Decorrelation of multiple scattered light, which isolates single scattering events at the expense of a reduced signal-to-noise ratio, has been proven to work using the two-colour crosscorrelation scheme.
Characterization of quantum dot/conducting polymer hybrid films and their application to light-emitting diodes.
2009
Quantum dot/conducting polymer hybrid films are used to prepare light-emitting diodes (LEDs). The hybrid films (CdSe@ZnS quantum dots excellently dispersed in a conducting polymer matrix, see figure) are readily prepared by various solution-based processes and are also easily micropatterned. The LEDs exhibit a turn-on voltage of 4 V, an external quantum efficiency greater than 1.5%, and almost pure-green quantum-dot electroluminescence.