Carles Serrat

Control of excited-state population and vibrational coherence with shaped-resonant and near-resonant excitation

We investigated numerically and experimentally the enhancement of vibrational coherence and population transfer in solution using tailored pulses. The general control mechanism is based on the precise control of the absorption after excitation with multipulses. Transient absorption was used as an experimental method to quantify the enhancement after the excitation with a shaped pump pulse in the low-pulse energy regime. A density-matrix approach was used to investigate the effect of the shaped excitation of a four-level system (two ground-state vibrational levels + two excited-state vibrational levels). Density-matrix simulation results suggest similar wavelength dependence as observed in the transient absorption experiment. The results show that enhancement of population transfer and vibrational coherence depends crucially on the overlap between the excitation pulse spectrum and the molecular absorption band.

Predicting availability functions in time-dependent complex systems with SAEDES simulation algorithms

Abstract In this paper, we propose the use of discrete-event simulation (DES) as an efficient methodology to obtain estimates of both survival and availability functions in time-dependent real systems—such as telecommunication networks or distributed computer systems. We discuss the use of DES in reliability and availability studies, not only as an alternative to the use of analytical and probabilistic methods, but also as a complementary way to: (i) achieve a better understanding of the system internal behavior and (ii) find out the relevance of each component under reliability/availability considerations. Specifically, this paper describes a general methodology and two DES algorithms, called SAEDES, which can be used to analyze a wide range of time-dependent complex systems, including those presenting multiple states, dependencies among failure/repair times or non-perfect maintenance policies. These algorithms can provide valuable information, specially during the design stages, where different scenarios can be compared in order to select a system design offering adequate reliability and availability levels. Two case studies are discussed, using a C/C++ implementation of the SAEDES algorithms, to show some potential applications of our approach.

Asymmetric and delayed activation of side modes in multimode semiconductor lasers with optical feedback

We study the multimode dynamics of a semiconductor laser with optical feedback operating in the low-frequency fluctuation regime. A multimode extension of the Lang–Kobayashi (LK) model shows, in agreement with experimental observations, that the low-frequency power dropouts exhibited by the main modes are accompanied by sudden, asymmetric, activations of dormant longitudinal side modes. Furthermore, these activations are delayed with respect to the dropouts of the active modes. In order to satisfactorily reproduce both the asymmetric activation of side modes and their delay with respect to the dropouts, the generalized LK model has to include a parabolic gain profile, together with a frequency shift of the gain curve with carrier population.

Polarization chaos in an optically pumped laser.

We study the steady-state and dynamic behavior of an optically pumped J = 0 ? J = 1 ? J = 0 laser operating with an isotropic ring cavity and an axial magnetic field. The gain anisotropy induced by a linearly polarized pump-laser f ield leads, in the steady state, to locking of the two circularly polarized components of the laser field, which acquires a linear polarization parallel to that of the pump field. In the presence of laser intensity instabilities, however, locking does not occur, and polarization instabilities appear. For the f irst time to our knowledge, polarization chaos has been found in a laser system.

Applications of discrete-event simulation to reliability and availability assessment in civil engineering structures

This paper discusses the convenience of predicting, quantitatively, time-dependent reliability and availability levels associated with most building or civil engineering structures. Then, the paper reviews different approaches to these problems and proposes the use of discrete-event simulation as the most realistic way to deal with them, specially during the design stage. The paper also reviews previous work on the use of both Monte Carlo simulation and discrete-event simulation in this area and shows how discrete-event simulation, in particular, could be employed to solve uncertainty in time-dependent structural reliability problems. Finally, a case study is developed to illustrate some of the concepts previously covered in the paper.

Coherent control of ultrafast optical four-wave mixing with two-color ω − 3 ω laser pulses

A theoretical investigation on the quantum control of optical coherent four-wave mixing interactions in two-level systems driven by two intense synchronized femtosecond laser pulses of central angular frequencies

Using simulation to determine reliability and availability of telecommunication networks

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Frequentist and Bayesian approaches for a joint model for prostate cancer risk and longitudinal prostate-specific antigen data

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A statistical learning based approach for parameter fine-tuning of metaheuristics

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Coherent amplification of attosecond light pulses in the water-window spectral region

is reported. By numerically solving the full Maxwell-Bloch equations beyond the slowly-varying envelope and rotating-wave approximations in the time domain, the nonlinear coupling to the optical field at frequency