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Leblond H.,University of Angers | Mihalache D.,University of Angers | Mihalache D.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Mihalache D.,Academy of Romanian Scientists
Physics Reports | Year: 2013

In the past years there was a huge interest in experimental and theoretical studies in the area of few-optical-cycle pulses and in the broader fast growing field of the so-called extreme nonlinear optics. This review concentrates on theoretical studies performed in the past decade concerning the description of few optical cycle solitons beyond the slowly varying envelope approximation (SVEA). Here we systematically use the powerful reductive expansion method (alias multiscale analysis) in order to derive simple integrable and nonintegrable evolution models describing both nonlinear wave propagation and interaction of ultrashort (femtosecond) pulses. To this aim we perform the multiple scale analysis on the Maxwell-Bloch equations and the corresponding Schrödinger-von Neumann equation for the density matrix of two-level atoms. We analyze in detail both long-wave and short-wave propagation models. The propagation of ultrashort few-optical-cycle solitons in quadratic and cubic nonlinear media are adequately described by generic integrable and nonintegrable nonlinear evolution equations such as the Korteweg-de Vries equation, the modified Korteweg-de Vries equation, the complex modified Korteweg-de Vries equation, the sine-Gordon equation, the cubic generalized Kadomtsev-Petviashvili equation, and the two-dimensional sine-Gordon equation. Moreover, we consider the propagation of few-cycle optical solitons in both (1+1)- and (2+1)-dimensional physical settings. A generalized modified Korteweg-de Vries equation is introduced in order to describe robust few-optical-cycle dissipative solitons. We investigate in detail the existence and robustness of both linearly polarized and circularly polarized few-cycle solitons, that is, we also take into account the effect of the vectorial nature of the electric field. Some of these results concerning the systematic use of the reductive expansion method beyond the SVEA can be relatively easily extended to few-cycle solitons in the general case of multilevel atoms. Prospects of the studies overviewed in this work are given in the conclusions. © 2012 Elsevier B.V.


Leblond H.,University of Angers | Mihalache D.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Mihalache D.,Academy of Romanian Scientists
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

By using a reductive perturbation technique applied to a two-level model, this study puts forward a generic two-dimensional sine-Gordon evolution equation governing the propagation of femtosecond spatiotemporal optical solitons in Kerr media beyond the slowly varying envelope approximation. Direct numerical simulations show that, in contrast to the long-wave approximation, no collapse occurs, and that robust (2+1)-dimensional ultrashort light bullets may form from adequately chosen few-cycle input spatiotemporal wave forms. In contrast to the case of quadratic nonlinearity, the light bullets oscillate in both space and time and are therefore not steady-state lumps. © 2010 The American Physical Society.


Tudor T.,University of Bucharest | Tudor T.,Academy of Romanian Scientists
Optics Letters | Year: 2014

An analysis of the operators of some widespread nonorthogonal polarizers is performed on the basis of the polar factorization theorem, in pure operatorial (nonmatrix) Dirac algebraic language. The role of the unitary polar component as a converter of the two sets of singular eigenvectors of the operator, one in the other, is emphasized in each case; this role is maintained for the singular operators corresponding to these special nonorthogonal polarizers. © 2014 Optical Society of America.


Delion D.S.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Delion D.S.,Academy of Romanian Scientists | Delion D.S.,Bioterra University | Liotta R.J.,University of Stockholm
Physical Review C - Nuclear Physics | Year: 2013

It is shown that the standard shell-model representation is inadequate to explain cluster decay processes due to a deficient asymptotic behavior of the corresponding single-particle wave functions. A new representation is proposed which is derived from a mean field consisting of the standard Woods-Saxon plus spin-orbit potential of the shell model, with an additional attractive pocket potential of a Gaussian form localized on the nuclear surface. The eigenvectors of this new mean field provide a representation which retains all the benefits of the standard shell model while at the same time reproducing well the experimental absolute α-decay widths from heavy nuclei. © 2013 American Physical Society.


Ixaru L.G.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Ixaru L.G.,Academy of Romanian Scientists
Computer Physics Communications | Year: 2010

The method consists in a flexible transformation of the 2D problem into a set of 1D single and coupled channel problems. This set of problems is then solved numerically by some highly tuned codes. By choosing codes based on CP methods and formulating an ad-hoc shooting procedure for the localization of the eigenenergies we obtain a version which is very efficient for speed and memory requirements. Extension of the method to more dimensions is also possible. © 2010 Elsevier Ltd. All rights reserved.


Raduta A.A.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Raduta A.A.,Academy of Romanian Scientists | Buganu P.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Physical Review C - Nuclear Physics | Year: 2011

The liquid drop Hamiltonian is amended with a potential which allows us to separate, in the intrinsic frame, the equations for β and γ coordinates. The Schrödinger equation for β is that for a sextic oscillator plus a centrifugal term, while that for γ is just the equation for the Mathieu function. The total energy has a compact form. The operator for the electric quadrupole transitions is considered in the intrinsic frame and involves two parameters accompanying the harmonic and anharmonic components. The parameters determining the energies as well as those defining the transition operator are to be determined by a fitting procedure. Applications refer to five isotopes: Os188, Os190, Os192, Th228, and Th230. Results are in good agreement with the corresponding experimental data. Results are also compared with those obtained within the coherent state model. A possible connection between the two formalisms is pointed out. © 2011 American Physical Society.


He Y.,Guangdong Polytechnic Normal University | Mihalache D.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Mihalache D.,Academy of Romanian Scientists
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We report the existence, stability, and rich dynamics of dissipative lattice solitons in optical media described by the cubic-quintic complex Ginzburg-Landau model with parity-time (PT) symmetric potentials. We focus on studying the generic spatial soliton propagation scenarios by changing (a) the linear loss coefficient in the complex Ginzburg-Landau model, (b) the amplitudes, and (c) the periods of real and imaginary parts of the complex-valued PT-symmetric optical lattice potential. Generically, it is found that if the period of the real part of the PT-symmetric optical lattice potential is close to π, the spatial solitons are tightly bound and they can propagate straightly along the lattice, while if the period of the real part of the PT-symmetric optical lattice potential is larger than π, the launched solitons are loosely bound and they can exhibit either a transverse (lateral) drift or a persistent swing around the input launching point due to gradient force arising from the spatially inhomogeneous loss. These latter features are intimately related to the dissipative nature of the system under consideration because they do not arise in the conservative counterpart of the dynamical model. These generic propagation scenarios can be effectively managed by properly changing the profile of the spatially inhomogeneous loss. © 2013 American Physical Society.


Raduta A.A.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Raduta A.A.,Academy of Romanian Scientists | Buganu P.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Physical Review C - Nuclear Physics | Year: 2013

Energies of the ground, β and γ bands as well as the associated B(E2) values are determined for each even-even isotope of the 180-196Pt chain by the exact solutions of some differential equations which approximate the generalized Bohr-Mottelson Hamiltonian. The emerging approaches are called the sextic and spheroidal approach (SSA), the sextic and Mathieu approach (SMA), the infinite square well and spheroidal approach (ISWSA), and the infinite square well and Mathieu approach (ISWMA). While the first three methods were formulated in some earlier papers, ISWMA is an unedited approach of this work. Numerical results are compared with those obtained with the so-called X(5) and Z(5) models. A contour plot for the probability density as function of the intrinsic dynamic deformations is given for a few states of the three considered bands with the aim of evidencing the shape evolution along the isotope chain and pointing out possible shape coexistence. © 2013 American Physical Society.


He Y.,Guangdong Polytechnic Normal University | Mihalache D.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Mihalache D.,Academy of Romanian Scientists
Journal of the Optical Society of America B: Optical Physics | Year: 2012

We study the rich dynamics of dissipative spatial solitons in optical media described by the complex Ginzburg-Landau equation in the presence of periodic, sinusoidal-type spatially inhomogeneous losses. It is revealed that in the case when the soliton is launched at the point where the periodic spatial modulation loss profile has its zero value, the gradient force of the inhomogeneous loss easily induces three generic propagation scenarios: (a) soliton transverse drift, (b) persistent swing around the soliton input launching position, and (c) damped oscillations near or even far from the input position. The soliton exhibiting damped oscillations eventually evolves into a stable one, whose output position can be controlled by the amplitude of the inhomogeneous loss profile. Conversely, when the launching point coincides with an extremum (a maximum or a minimum) of the sinusoidal-type loss landscape, both soliton transverse drift and soliton damped oscillations occur due to transverse modulation instability. Moreover, in this case, depending on the balance between the amplitude of the inhomogeneous loss modulation profile and the homogeneous linear loss coefficient, either the launched soliton can maintain its stable propagation at the input position or a stable plump dissipative soliton can be formed while preserving the launching point. © 2012 Optical Society of America.


Ixaru L.G.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Ixaru L.G.,Academy of Romanian Scientists
Computer Physics Communications | Year: 2012

The family of the simplest three-stage explicit Runge-Kutta methods is examined by a conveniently adapted form of the exponential fitting approach. We obtain versions whose unusual feature is that their coefficients are no longer constant, as in the standard version, but depend on the equation to be solved. Two mathematical properties of the new versions are specially helpful for applications. Firstly, although in general the order is three, that is the same as for the standard method, this can be easily increased to four by a suitable choice of the position of the stage abscissas. Secondly, the stability properties are massively enhanced. In particular, two versions of order four are A-stable, a fact which is quite unusual for explicit methods. © 2011 Elsevier B.V. All rights reserved.

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