Search results for "Time-resolved"
showing 10 items of 70 documents
Effects induced by UV laser radiation on the blue luminescence of silica nanoparticles
2013
The effects induced on the blue luminescence centered around 2.8 eV, characteristic of silica nanoparticles, were investigated by monitoring its intensity during and after exposure to the third and the fourth harmonic of a Nd:YAG pulsed laser. The luminescence trend is found to be dependent on the UV photon energy: 3.50 eV photons induce a partial bleaching followed by a recovery in the post-irradiation stage; 4.66 eV photons cause a total bleaching permanent after the irradiation. These results are interpreted as the conversion of luminescent defects towards stable and metastable configurations.
Exact reconstruction of thz sub-λ source features in knife-edge measurements
2013
The spatial features of a sub-wavelength terahertz source are not accessible using time-integrated knife-edge techniques due to the non-separable space-time nature of the radiated field and to systematic modifications induced by the blade itself. We show that combining knife-edge with a time resolved electro-optical sampling, the space-time coupling can be addressed and the source field profile can be exactly reconstructed.
Optical Spectroscopy of Short-Lived Isotopes
1979
This chapter will concentrate on a special branch of the large field of optical spectroscopy, namely, the study of hyperfine structure (hfs) and isotope shift (IS) of short-lived isotopes. Such investigations give information on some basic properties of these nuclei: the spin ( ), the magnetic moment (μI), the spectroscopic quadrupole moment (Q s ), and the change of the mean square charge radius between different isotopes (δ〈r 2〉).
The Collinear Fast Beam laser Spectroscopy (Cfbs) experiment at Triumf
2016
Abstract Laser spectroscopy experiments at radioactive ion beam facilities around the world investigate properties of exotic nuclei for scientific endeavours such as, but not limited to, the investigation of nuclear structure. Advancements in experimental sensitivity and performance are continuously needed in order to extend the reach of nuclei that can be measured. The collinear fast beam laser spectroscopy ( Cfbs ) setup at Triumf , coupled to an out-of-plane radio-frequency quadrupole Paul trap, enables measurements of some of the most fundamental nuclear properties for long-lived ground and isomeric states. The first comprehensive overview of the Cfbs experiment is provided along with d…
Quantum control of ground-state rotational coherence in a linear molecule
2000
We present an experimental and theoretical investigation of the quantum control of ground-state rotational coherence in a linear molecule. A sequence of two temporally separated laser pulses creates a rotational superposition state in ${\mathrm{CO}}_{2}$ whose evolution is monitored through a polarization technique. We study the influence of the phase difference between the two pulses. We show that the overlapping of the two wave packets, produced by each pulse, gives rise to quantum interference that affects the orientational anisotropy of the sample. Because of the large number of coherently excited levels, the interference produces well-separated temporal structures, whose magnitude can …
Mechanism‐Dependent Modulation of Ultrafast Interfacial Water Dynamics in Intrinsically Disordered Protein Complexes
2018
Abstract The recognition of intrinsically disordered proteins (IDPs) is highly dependent on dynamics owing to the lack of structure. Here we studied the interplay between dynamics and molecular recognition in IDPs with a combination of time‐resolving tools on timescales ranging from femtoseconds to nanoseconds. We interrogated conformational dynamics and surface water dynamics and its attenuation upon partner binding using two IDPs, IBB and Nup153FG, both of central relevance to the nucleocytoplasmic transport machinery. These proteins bind the same nuclear transport receptor (Importinβ) with drastically different binding mechanisms, coupled folding–binding and fuzzy complex formation, resp…
Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy
2014
Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards understanding its mechanism. Protonation and conformational changes affect the vibration pattern of amino acid side chains and of the peptide bond, respectively, both of which can be probed by infrared (IR) difference spectroscopy. For proteins whose function can be repetitively and reproducibly triggered by light, it is possible to obtain infrared difference spectra with (sub)microsecond resolution over a broad spectral range using the step-scan Fourier transform infrared technique. With -10(2)-10(3) repetitions of the photoreaction, the minimum num…
Quantum confinement effects observed by the photoluminescence of SiOx/SiO2 multilayers
2012
Spectral and decay features related to the red emission from Si nanocrystals were investigated by time-resolved photoluminescence spectra carried out on SiOx/SiO2 nanosized multilayers. On decreasing the SiOx thickness from 8.4 nm to 2.2 nm this luminescence band exhibits a blue-shift from 1.65 eV to 1.75 eV and its lifetime increases from 12μs to 17 μs. These results are discussed on the basis of previous models proposed in literature and agree with quantum confinement effects arising from differently sized Si nanocrystals in our samples.
Defect-related visible luminescence of silica nanoparticles
2013
The high photon emissivity in the visible spectral range is one of the most relevant phenomena emerging from the reduction of silica down to nanoscale; hence it is promising for the development of optical nanotechnologies (down converter, probes, display). It is well accepted that the origin of this luminescence is related to the high specific surface (~100 m2/g) that favors the formation of optically active defects at the nanosilica surface. With the aim to clarify the role of specific luminescent defects, here we report a detailed study of spectral and decay features by time-resolved photoluminescence spectra under a visible-UV tunable laser excitation. Our study is carried out on differe…
Luminescence from nearly isolated surface defects in silica nanoparticles
2015
A structured emission/excitation pattern, proper of isolated defects, arises in a vacuum from silica nanoparticles. The luminescence, centered around 3.0-3.5 eV, is characterised by a vibronic progression due to the phonon coupling with two localised modes of frequency ∼1370 cm(-1) and ∼360 cm(-1), and decays in about 300 ns at 10 K. On increasing the temperature, the intensity and the lifetime decrease due to the activation of a non-radiative rate from the excited state. Concurrently, the temperature dependence of the lineshape evidences the low coupling with non-localised modes of the matrix (Huang-Rhys factor S ~ 0.2) and the poor influence of the inhomogeneous broadening. These findin…