31 research outputs found
Wavelet analysis on symbolic sequences and two-fold de Bruijn sequences
The concept of symbolic sequences play important role in study of complex
systems. In the work we are interested in ultrametric structure of the set of
cyclic sequences naturally arising in theory of dynamical systems. Aimed at
construction of analytic and numerical methods for investigation of clusters we
introduce operator language on the space of symbolic sequences and propose an
approach based on wavelet analysis for study of the cluster hierarchy. The
analytic power of the approach is demonstrated by derivation of a formula for
counting of {\it two-fold de Bruijn sequences}, the extension of the notion of
de Bruijn sequences. Possible advantages of the developed description is also
discussed in context of applied
Accumulation effects in modulation spectroscopy with high repetition rate pulses: recursive solution of optical Bloch equations
Application of the phase modulated pulsed light for advance spectroscopic
measurements is the area of growing interest. The phase modulation of the light
causes modulation of the signal. Separation of the spectral components of the
modulations allows to distinguish the contributions of various interaction
pathways. The lasers with high repetition rate used in such experiments can
lead to appearance of the accumulation effects, which become especially
pronounced in systems with long-living excited states. Recently it was shown,
that such accumulation effects can be used to evaluate parameters of the
dynamical processes in the material. In this work we demonstrate that the
accumulation effects are also important in the quantum characteristics
measurements provided by modulation spectroscopy. In particular, we consider a
model of quantum two-level system driven by a train of phase-modulated light
pulses, organised in analogy with the 2D spectroscopy experiments. We evaluate
the harmonics' amplitudes in the fluorescent signal and calculate corrections
appearing from the accumulation effects. We show that the corrections can be
significant and have to be taken into account at analysis of experimental data.Comment: 10 pages, 5 figure
Vibration Assisted Polariton Wavefunction Evolution in Organic Nanofibers
Formation of the composite photonic-excitonic particles, known as polaritons,
is an emerging phenomenon in materials possessing strong coupling to light. The
organic-based materials besides the strong light-matter interaction also
demonstrate strong interaction of electronic and vibrational degrees of
freedom. We utilize the Dirac-Frenkel variation principle to derive
semiclassical equations for the vibration-assisted polariton wavefunction
evolution when both types of interactions are treated as equally strong. By
means of the approach, we study details of the polariton relaxation process and
the mechanism of the polariton light emission. In particular, we propose the
photon emission mechanism, which is realized when the polariton wave package
exceeds the geometrical size of the nanosystem. To verify our conclusions we
reproduce the fluorescence peak observed in experiment (Takazawa
\textit{et.al.} Phys.Rev.Let. \textbf{105}:07401, 2010) and estimate the
light-matter interaction parameter
Clustering of periodic orbits and ensembles of truncated unitary matrices
Periodic orbits in chaotic systems form clusters, whose elements traverse
approximately the same points of the phase space. The distribution of cluster
sizes depends on the length n of orbits and the parameter p which controls
closeness of orbits actions. We show that counting of cluster sizes in the
baker's map can be turned into a spectral problem for an ensemble of truncated
unitary matrices. Based on the conjecture of the universality for the
eigenvalues distribution at the spectral edge of these ensembles, we obtain
asymptotics of the second moment of cluster distribution in a regime where both
n and p tend to infinity. This result allows us to estimate the average cluster
size as a function of the number of encounters in periodic orbits.Comment: 16 pages, 5 figure
The nature of relaxation processes revealed by the action signals of phase modulated light fields
We introduce a generalized theoretical approach to study action signals
induced by the absorption of two-photons from two phase modulated laser beams
and subject it to experimental testing for two types of photoactive samples,
solution of rhodamine 6G and GaP photodiode. In our experiment, the phases of
the laser beams are modulated at the frequencies f1 and f2, respectively. The
action signals, such as photoluminescence and photocurrent, which result from
the absorption of two photons, are isolated at frequencies m f (f=|f1-f2|,
m=0,1,2...). We demonstrate that the ratio of the amplitudes of the secondary
(m=2) and the primary (m=1) signals is sensitive to the type of relaxation
process taken place in the system and thus can be used for its identification.
Such sensitivity originates from cumulative effects of non-equilibrated state
of the system between the light pulses. When the cumulative effects are small,
i.e. the relaxation time is much shorter then the laser repetition rate or the
laser intensity is high enough to dominate the system behavior, the ratio
achieves its reference value 1:4 (the signature of two-photon absorption). In
the intermediate regimes the ratio changes rapidly with the growth of intensity
from zero value in case of second order relaxation process, while it
demonstrates slow monotonic decrease for linear relaxation. In the article we
also determine the value of the recombination rate in a GaP photodiode by using
the above approach