Search results for "laser"
showing 10 items of 3161 documents
MAGNETO-OPTICAL EFFECTS IN RUBIDIUM VAPOR AND NITROGEN{VACANCY CENTERS IN DIAMOND
2021
Promocijas darba pirmā daļa apraksta gaismas polarizācijas plaknes griešanu, ierosinot rubīdija pāreju 52S1/2 −→ 62P1/2. Šajā daļā tiek apskatīta daļēji izšķirtas supersīkstruktūras, kā arī pamatstāvokļa repopulācijas, kas notiek caur starp-stāvokļiem, ietekme uz rotācijas signāliem. Otrā promocijas darba daļa ietver modeļus, kas izveidoti, lai aprakstītu optiski detektējamas magnētiskās rezonanses signālus un dinamiskās kodola spina polarizācijas signālus slāpekļa–vakances centros dimanta kristālā. Izstrādātie modeļi ir balstīti uz Liuvilla vienādojumiem kvantu sistēmām. Visu promocijas darbā izstrādāto modeļa testēšanai tika izmantoti eksperimentālie dati. Atslēgas vārdi rubīdijs, nelineā…
Dynamical Stark Effect in the nu(2)/nu(4) Vibrational Polyad of SiH(4): Theory and Observation.
2000
We report a theoretical and experimental investigation of the dynamical Stark effect in a tetrahedral molecule, silane (SiH(4)). We use a tetrahedral formalism and Floquet theory to calculate the absorption spectra for the molecule dressed by an intense nonresonant pulsed laser. Experimentally, the dynamical Stark effect is observed for transitions of the nu(2)/nu(4) vibrational polyad of SiH(4) by means of nanosecond diode laser absorption spectroscopy and a Nd:YAG laser excitation. Copyright 2000 Academic Press.
Coherent destruction of tunneling in a six-dimensional model of NHD2: a computational study using the multi-configuration time-dependent Hartree meth…
2014
We investigate the phenomenon of coherent destruction of tunneling in a six-dimensional model of the NHD2 molecule. Two regimes are considered for the frequency of the laser field. A non-resonant regime where the frequency of the laser field is high with respect to the ground vibrational state tunneling splitting but smaller than the transition frequencies between the ground and excited vibrational states; and a quasi-resonant regime where the frequency of the laser field is close to the transition frequency between the ground and first excited vibrational states. In each case, we study the laser driven dynamics in the framework of the Floquet formalism and derive simple analytical formulas…
Effect of laser radiation upon heat and mass transfer in two-component elastic semitransparent layer
2004
Abstract In present paper the effect of the correlation between spectral radiative characteristics of different lasers and absorptive characteristics of laser irradiated two-component elastic semitransparent material upon coupled thermal, diffusive and elastic processes in the layer is examined. Irradiated material is supposed to consist of elastic matrix and gaseous admixture. Investigations are carried out within the model applied early to the study of mentioned coupled processes in the layer subjected to thermal infrared radiation. Calculations were carried out for four different infrared lasers. Peculiarities of heat and admixture mass transfer caused by laser irradiation are establishe…
Long- and short-term stability of all polarization-maintaining thulium doped passively mode-locked fiber lasers with emission wavelengths at 1.95 µm …
2023
In this work, we compare the operation of a passively modelocked polarization-maintaining emission in two thulium-doped fiber lasers pumped at 1561 nm, with emission at wavelengths of 1.951 μm in one case and 2.07 μm in the other. We obtained a sequence of light pulses at 15.6 MHz, whose temporal width was 81 ps at 1.95 μm, and a sequence of light pulses at 13.1 MHz, whose temporal width was 94 ps at 2.07 μm. Finally, we also measured the long-term stability of this setup during a 24-h operation, as well as the short-term stability in a simulated harsh environment. The results confirm the superior performance of fiber laser systems with a fully polarization-maintaining design.
Laser-Induced Fluorescence Imaging of Paper Surfaces
1993
Laser-induced fluorescence imaging has been used to study the microstructure of paper surfaces. Pulses from a XeCl-excimer laser, 10 ns in duration at 308 nm, were used for excitation, and fluorescence was collected at 420 nm. The excitation spot diameter was approximately 20 µm, and the sampling interval 0.15 mm. Within an area of 5*5 mm2, 1023 sampling points were recorded to generate 3D fluorescence maps of paper surfaces. Papers containing fluorescence whitening agents (FWAs) gave the highest average fluorescence signals. Coated papers with no FW As show weaker signals than the base sheet. For some thirty different paper samples, an obvious correlation between the amount of coating and…
Towards combined multispectral, FLIM and Raman imaging for skin diagnostics
2020
To explore challenges for further improvement of diagnostic performance, a project aimed at development of technology for tri-modal skin imaging by combining multispectral, fluorescence lifetime and Raman band imaging was initiated. In this study, each of the mentioned imaging modalities has been preliminary tested and updated. Four different multispectral imaging devices were tested on color standards. Picosecond laser-excited fluorescence lifetime imaging equipment was examined on ex-vivo skin samples. Finally, a new Raman spectroscopy setup with 785 nm laser was launched and tested on cell cultures and ex-vivo skin. Advantages and specific features of the tri-modal skin imaging are discu…
Testing a portable laser-induced breakdown spectroscopy system on geological samples.
2012
9 pages; International audience; This paper illustrates the potentialities of a home-made portable LIBS (laser-induced breakdown spectroscopy) instrument in Earth sciences, more particularly in geochemically recognizing (i) tephra layers in lacustrine sediments and (ii) fossilization processes in ammonites. Abundances for selected lines of Al, Ca, Fe, Ti, Ba and Na were determined in lacustrine chalk sediments of the Jura, where the Laacher See Tephra (LST) layer is recorded. A statistical treatment of elemental maps produced from the section of a sedimentary column containing the LST event allows instrumental conditions to be optimized. Accumulating spectra from close shot positions gives …
Tecniche avanzate per il rilevamento e la valorizzazione dei beni culturali. La chiesa rupestre di San Nicolò a Modica (RG)
2011
La Geomatica mette oggi a disposizione degli operatori che a vario titolo si occupano di beni culturali (storici, tecnici delle Soprintendenze, specialisti del recupero e del restauro, o anche solo studiosi) tecniche e strumentazioni di rilevamento sempre più veloci, accurate, affidabili. Spesso, la complessità della geometria dei manufatti da rilevare richiede l’uso di metodologie differenti ma integrate fra loro. Questo è, ad esempio, il caso del rilevamento della chiesa rupestre di San Nicolò a Modica per il quale si è fatto ricorso all’impiego di tecniche laser-scanning e fotogrammetriche digitali integrate. Questa integrazione ha permesso di ottenere un modello 3D virtuale foto realist…
Core hole screening and decay rates of double core ionized first row hydrides.
2013
Because of the high intensity, X-ray free electron lasers allow one to create and probe double core ionized states in molecules. The decay of these multiple core ionized states crucially determines the evolution of radiation damage in single molecule diffractive imaging experiments. Here we have studied the Auger decay in hydrides of first row elements after single and double core ionization by quantum mechanical ab initio calculations. In our approach the continuum wave function of the emitted Auger electron is expanded into spherical harmonics on a radial grid. The obtained decay rates of double K-shell vacancies were found to be systematically larger than those for the respective single …