Search results for "Physics::Optics"
showing 10 items of 1958 documents
Strong coupling between surface plasmon polaritons and \beta-carotene in nanolayered system
2013
In this article we experimentally demonstrate the strong coupling between surface plasmon polaritons (SPP) and the S2 state of β-carotene. The SPPs are excited by prism coupling technique on a thin silver film with β-carotene embedded in a polymer layer on top of that. Rabi splittings with energies 80 and 130 meV are observed in the recorded dispersion relations. Both coupled oscillator model and transfer matrix method are used to fit the experimental results. The scattered radiation of the propagating strongly coupled SPP-S2 hybrids is collected and an increase of the low energy splitting to 120 meV is observed compared to the reflectivity data. In addition, we performed molecule excitatio…
Kohn-Sham Decomposition in Real-Time Time-Dependent Density-Functional Theory An Efficient Tool for Analyzing Plasmonic Excitations
2017
The real-time-propagation formulation of time-dependent density-functional theory (RT-TDDFT) is an efficient method for modeling the optical response of molecules and nanoparticles. Compared to the widely adopted linear-response TDDFT approaches based on, e.g., the Casida equations, RT-TDDFT appears, however, lacking efficient analysis methods. This applies in particular to a decomposition of the response in the basis of the underlying single-electron states. In this work, we overcome this limitation by developing an analysis method for obtaining the Kohn-Sham electron-hole decomposition in RT-TDDFT. We demonstrate the equivalence between the developed method and the Casida approach by a be…
Analysis of FBG reflection spectra under uniform and non-uniform transverse loads
2019
Loads applied transversely on the external surface of waveguides change their circular cross-sectional geometry generating birefringence. Due to this effect the reflected spectrum of a Fibre Bragg grating (FBG) undergoes a splitting of the single peak of the Bragg wavelength. In this work, we employed the Transfer Matrix Method (TMM) for x- and y-polarized wave-modes to model the uniform FBG reflection spectra for uniform and non-uniform transverse loads. We also performed experimental measurements for two different transverse load scenarios. The load profiles chosen for these experiments were applied on the FBG sensor through a block of steel and a roll bearing pin. Then, the modelled and …
Orbital angular momentum parton distributions in quark models
1999
At the low energy, {\sl hadronic}, scale we calculate Orbital Angular Momentum (OAM) twist-two parton distributions for the relativistic MIT bag model and for non-relativistic quark models. We reach the scale of the data by leading order evolution in perturbative QCD. We confirm that the contribution of quarks and gluons OAM to the nucleon spin grows with $Q^2$, and it can be relevant at the experimental scale, even if it is negligible at the hadronic scale, irrespective of the model used. The sign and shape of the quark OAM distribution at high $Q^2$ may depend strongly on the relative size of the OAM and spin distributions at the hadronic scale. Sizeable quark OAM distributions at the had…
LU FMOF Optometrijas un redzes zinātnes nodaļas un Latvijas optometristu un optiķu asociācijas konferenču referātu tēzes
2022
Tēzes no LU 80.Starptautiskās zinātniskās konferences Cilvēka fizioloģijas un uztveres sēdes un LU Optometrijas un redzes zinātnes nodaļas un LOOA kopīgās klīniski praktiskās konferences Rīgā, 2022. gada 11. un 13. februārī
Cilvēka fizioloģijas un uztveres aktuālie pētījumi 2021. gadā
2021
Šajā izdevumā apkopoti LU FMOF Optometrijas un redzes zinātnes nodaļas un tās sadarbības partneru aktuālie pētījumi par cilvēka fizioloģiju un uztveri 2021. gadā. Pētījumi ir saistīti ar redzes zinātni un klīnisko optometriju.
Nonlinear Absorption and Refraction of Picosecond and Femtosecond Pulses in HgTe Quantum Dot Films
2021
We report measurements of the saturated intensities, saturable absorption, and nonlinear refraction in 70-nm thick films containing 4 nm HgTe quantum dots. We demonstrate strong nonlinear refraction and saturable absorption in the thin films using tunable picosecond and femtosecond pulses. Studies were carried out using tunable laser pulses in the range of 400–1100 nm. A significant variation of the nonlinear refraction along this spectral range was demonstrated. The maximal values of the nonlinear absorption coefficients and nonlinear refractive indices determined within the studied wavelength range were −2.4 × 10−5 cm2 W−1 (in the case of 28 ps, 700 nm probe pulses) and −3 × 10−9 cm2 W−1 …
Time resolved emission at 1.3 μm of a single InAs quantum dot by using a tunable fibre Bragg grating
2013
Photoluminescence and time resolved photoluminescence from single metamorphic InAs/GaAs quantum dots (QDs) emitting at 1.3 mu m have been measured by means of a novel fibre-based characterization set-up. We demonstrate that the use of a wavelength tunable fibre Bragg grating filter increases the light collection efficiency by more than one order of magnitude as compared to a conventional grating monochromator. We identified single charged exciton and neutral biexciton transitions in the framework of a random population model. The QD recombination dynamics under pulsed excitation can be understood under the weak quantum confinement potential limit and the interaction between carriers at the …
Realization of time-resolved two-vacuum-ultraviolet-photon ionization
2009
International audience; Ultrafast dynamics of excited molecules is studied through time-resolved two-vacuum-ultraviolet (vuv)- photon ionization using a nonlinear volume autocorrelator unit. The two-vuv-photon process is induced by the intense fifth harmonic radiation of a femtosecond Ti:sapphire laser. In a proof-of-principle experiment, ultrafast dynamics of excited ethylene and oxygen molecules are investigated. Molecular decay times are deduced by comparing the experimental data with the results of a numerical model that accounts for the spatial and temporal characteristics of the harmonic field. The present experiments pave a convenient way for time domain investigations in the vuv-xuv s…
Surface plasmon polariton interaction with Sulforhodamine 101 dye
2011
The integration of conventional optical elements and electronic circuits is limited by size mismatch between these components. The diffraction limit does not allow miniaturizing optical elements to nm-scale. It was realized that light being strongly coupled to coherently oscillating electrons at the metal surface could be used to overcome this limit. The coupled state is called surface plasmon polariton. Surface plasmon polariton propagates in plane of metallic film within 10-100 μm range but decay exponentially in perpendicular directions to metal-dielectric boundary. Interaction of the surface plasmon polaritons with fluorescent dye molecules may result in development of new nanodimension…