3,341 research outputs found
Time-frequency methods for coherent spectroscopy
Time-frequency decomposition techniques, borrowed from the signal-processing field, have been adapted and applied to the analysis of 2D oscillating signals. While the Fourier-analysis techniques available so far are able to interpret the information content of the oscillating signal only in terms of its frequency components, the time-frequency transforms (TFT) proposed in this work can instead provide simultaneously frequency and time resolution, unveiling the dynamics of the relevant beating components, and supplying a valuable help in their interpretation. In order to fully exploit the potentiality of this method, several TFTs have been tested in the analysis of sample 2D data. Possible artifacts and sources of misinterpretation have been identified and discussed
Correlated Fluctuations and Intraband Dynamics of J-Aggregates Revealed by Combination of 2DES Schemes
The intraband exciton dynamics of molecular aggregates is a crucial initial step to determine the possibly coherent nature of energy transfer and its implications for the ensuing interband relaxation pathways in strongly coupled excitonic systems. In this work, we fully characterize the intraband dynamics in linear J-aggregates of porphyrins, good model systems for multichromophoric assemblies in biological antenna complexes. Using different 2D electronic spectroscopy schemes together with Raman spectroscopy and theoretical modeling, we provide a full characterization of the inner structure of the main one-exciton band of the porphyrin aggregates. We find that the redistribution of population within the band occurs with a characteristic time of 280 fs and dominates the modulation of an electronic coherence. While we do not find that the coupling to vibrations significantly affects the dynamics of excitonic coherence, our results suggest that exciton fluctuations are nevertheless highly correlated
Global analysis of coherence and population dynamics in 2D electronic spectroscopy
2D electronic spectroscopy is a widely exploited tool to study excited state dynamics. A high density of information is enclosed in 2D spectra. A crucial challenge is to objectively disentangle all the features of the third order optical signal. We propose a global analysis method based on the variable projection algorithm, which is able to reproduce simultaneously coherence and population dynamics of rephasing and non-rephasing contributions. Test measures at room temperature on a standard dye are used to validate the procedure and to discuss the advantages of the proposed methodology with respect to the currently employed analysis procedures
Isolating the chiral contribution in optical two-dimensional chiral spectroscopy using linearly polarized light
The full development of mono- or multi-dimensional time-resolved spectroscopy
techniques incorporating optical activity signals has been strongly hampered by
the challenge of identifying the small chiral signals over the large achiral
background. Here we propose a new methodology to isolate chiral signals
removing the achiral background from two commonly used configurations for
performing two dimensional optical spectroscopy, known as BOXCARS and GRadient
Assisted Photon Echo Spectroscopy (GRAPES). It is found that in both cases an
achiral signal from an isotropic system can be completely eliminated by small
manipulations of the relative angles between the linear polarizations of the
four input laser pulses. Starting from the formulation of a perturbative
expansion of the signal in the angle between the beams and the propagation
axis, we derive analytic expressions that can be used to estimate how to change
the polarization angles of the four pulses to minimize achiral contributions in
the studied configurations. The generalization to any other possible
experimental configurations has also been discussed. %We derive analytic
expressions to changes required to the polarizations in terms of a perturbative
expansion in the angle between the beams and the colinear axis. We also
numerically estimate higher order coefficients which cover arbitrarily large
angles and thus any experimental configuration.Comment: 7 figure
Fedosov Quantization and Perturbative Quantum Field Theory
Fedosov has described a geometro-algebraic method to construct in a canonical
way a deformation of the Poisson algebra associated with a finite-dimensional
symplectic manifold ("phase space"). His algorithm gives a non-commutative, but
associative, product (a so-called "star-product") between smooth phase space
functions parameterized by Planck's constant , which is treated as a
deformation parameter. In the limit as goes to zero, the star product
commutator goes to times the Poisson bracket, so in this sense his
method provides a quantization of the algebra of classical observables. In this
work, we develop a generalization of Fedosov's method which applies to the
infinite-dimensional symplectic "manifolds" that occur in Lagrangian field
theories. We show that the procedure remains mathematically well-defined, and
we explain the relationship of this method to more standard perturbative
quantization schemes in quantum field theory.Comment: This is a preprint (with minor modifications) of my doctoral thesis,
which is being submitted to Fakult\"at f\"ur Physik und Geowissenschaften -
Universit\"at Leipzig. 169 pages, 3 figures, 2 table
La modellazione microstrutturale di materiali a struttura eterogenea: princìpi ed applicazioni
Molti problemi della Meccanica e Fisica dei Solidi e della Scienza dei Materiali, non sonofacilmente risolvibili con gli approcci tradizionali. Oltre allo studio delle proprietà effettive dei solidi eterogenei,vi è la crescente necessità di incorporare un maggiore numero di informazioni sui meccanismi di deformazione edanneggiamento generati alla microscala, anche per i materiali abitualmente considerati omogenei.Micromeccanismi di cavitazione e concentrazioni locali di tensione e deformazione, sono indispensabili perspiegare fenomeni non-lineari come la rottura di fatica o il cedimento duttile, altrimenti non inquadrabili conapprocci classici di tensioni e deformazioni medie. La micromeccanica si occupa della determinazione precisa, odi una stima accurata, di grandezze di campo microstrutturali locali. In questo lavoro sono illustrati i princìpiche sono alla base dell’approccio micromeccanico, come i concetti di multiscala, di distribuzione statistica dellefasi, di descrizione mediante volumi di riferimento e di omogeneizzazione e localizzazione, e, attraverso alcuneapplicazioni pratiche delle principali tecniche di modellazione, sono illustrati e discussi criticamente i risultatidella ricerca effettuata su varie strutture di ghisa nodulare
POSFET tactile sensing arrays using CMOS technology
This work presents fabrication and evaluation of novel POSFET (Piezoelectric Oxide Semiconductor Field Effect Transistor) devices based tactile sensing chip. In the newer version presented here, the tactile sensing chip has been fabricated using CMOS (Complementary Metal Oxide Semiconductor) technology. The chip consists of 4 x 4 POSFET touch sensing devices (or taxels) and both, the individual taxels and the array are designed to match spatio–temporal performance of the human fingertips. To detect contact events, the taxels utilize the contact forces induced change in the polarization level of piezoelectric polymer (and hence change in the induced channel current of MOS). The POSFET device on the chip have linear response in the tested dynamic contact forces range of 0.01–3 N and the sensitivity (without amplification) is 102.4 mV/N
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