Search results

1

Quantum Optics of Atomic Wave-Packets

100%

Rzążewski K., Plaja-Rustein L., Pumares-Carceller L., Roso-Franco L., Żakowicz W.

Acta Physica Polonica A

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1994

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vol. 86

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issue 1

279-286

EN

Recent progress in production and control of the atomic wave-packets calls for re-examination of the most fundamental quantum optical processes. We have examined the evolution of the atomic wave-packet resonantly driven by the monochromatic laser beam and the spontaneous emission from an extended atom. We stress the role of Doppler shifts in the dephasing of the atomic dipole. New effects of single laser pulse photon echo and homogeneous Doppler modification of the emission line are discussed.

2

On the q-Analogue of a Black Body Radiation

80%

Babinec P.

Acta Physica Polonica A

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1992

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vol. 82

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issue 6

957-960

EN

A statistical distribution function and spectral energy density are derived for the q-analogue of a black body radiation. These functions are different from the usual ones for q ≠ 1 and they have singularities. The reason for these singularities is also discussed.

3

Phonon Effects on Population Inversion in Quantum Dots: Resonant, Detuned and Frequency-Swept Excitations

80%

Reiter D., Lüker S., Gawarecki K., Grodecka-Grad A., Machnikowski P., Axt V., Kuhn T.

Acta Physica Polonica A

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2012

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vol. 122

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issue 6

1065-1068

EN

The effect of acoustic phonons on different light-induced excitations of a semiconductor quantum dot is investigated. Resonant excitation of the quantum dot leads to the Rabi oscillations, which are damped due to the phonon interaction. When the excitation frequency is detuned, an occupation can only occur due to phonon absorption or emission processes. For frequency-swept excitations a population inversion is achieved through adiabatic rapid passage, but the inversion is also damped by phonons. For all three scenarios the influence of the phonons depends non-monotonically on the pulse area.

4

Ultrafast Coherent Control of Spin Precession Motion by Terahertz Magnetic Pulses

80%

Nakajima M., Yamaguchi K., Suemoto T.

Acta Physica Polonica A

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2012

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vol. 121

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issue 2

343-346

EN

We demonstrated coherent control of spin precession motion due to the ferromagnetic resonance induced by magnetic field component of ultrashort terahertz pulses. The amplitude of the precession can be controlled by the pulse separation time of the double pulse excitation technique. We succeeded in observing the energy transfer between spin and photon systems, and the energy of the spin system is returned to the second terahertz pulses instantaneously when the precession amplitude is cancelled.

5

Binding of Biexcitons in GaAs/AlGaAs Superlattices

80%

Mizeikis V., Birkedal D., Langbein W., Lyssenko V. G., Hvam J. M.

Acta Physica Polonica A

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1997

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vol. 92

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issue 5

923-928

EN

Binding of the heavy-hole excitons and biexcitons in GaAs/Al_{0.3}Ga_{0.7}As superlattices is studied using linear and nonlinear optical techniques. High biexciton binding energies characteristic of quasi two-dimensional biexcitons are observed in superlattices with considerable miniband dispersion.

6

Ultrafast Phenomena in II-VI Semiconductors

80%

Kalt H., Wachter S., Lüerssen D., Hoffmann J.

Acta Physica Polonica A

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1998

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vol. 94

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issue 2

139-146

EN

We review studies on the coherent and incoherent exciton dynamics in ZnSe-based quantum wells. First, the exciton-exciton scattering parameter is determined from femtosecond four-wave mixing as a function of background exciton density generated by a prepulse. A linear increase in the excitonic homogeneous linewidth is found as a function of the background exciton density with significant different scattering parameters for the cases of interaction with coherent or incoherent excitons. Second, the thermalization dynamics of spectrally narrow hot-exciton distributions is investigated by time-resolved phonon sideband spectroscopy. Thermalization assisted by acoustic phonons occurs on a 100 ps timescale, which is in good agreement with model calculations in time dependent perturbation theory.

7

Investigation of Radiation Trapping in Atomic Vapour Excited by Weak Resonant Laser Pulses

80%

Chorąży J., Stacewicz T.

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vol. 96

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issue 3-4

383-390

EN

We present results of our investigations on radiation trapping in sodium vapour excited to 3P level by weak laser pulses. The evolution of the fluorescence signal as well as the evolution of excited atoms distribution were studied using the Monte Carlo method. Some predictions of these investigations were checked experimentally.

8

Extreme Nonlinear Optics in Terms of Riccati-Type Equation

80%

Parzyński R., Plucińska A.

Acta Physica Polonica A

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2005

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vol. 108

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issue 6

959-969

EN

In an approach based on the nonlinear Riccati-type differential equation for the ratio of the level population amplitudes, rather than on the optical Bloch equations, we describe the response of a two-level system to a few-cycle light pulse of intensity from the regime of extreme nonlinear optics, i.e., when the Rabi and transition frequencies are comparable. Emphasis is put on the dependence of the spectra of the scattered light on the carrier-envelope phase, duration and strength of both resonant and off-resonant pulses.

9

The Light Harvesting Process in Purple Bacteria

80%

Krueger B., Scholes G., Yu J., Fleming G.

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vol. 95

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issue 1

63-83

EN

We present and review the results of fluorescence upconversion and photon echo experiments, and $ab initio$ calculations performed in our group within the last few years with respect to the light harvesting process in purple bacteria. Carotenoids transfer energy to bacteriochlorophyll (BChl) mainly via the carotenoid S_{2} → BChl Q_{x} pathway on a ~100 fs timescale. This transfer is reasonably reproduced by considering the Coulombic coupling calculated using the transition density cube method which is valid at all molecular separations. Carotenoids may also serve a role in mediating B800 → B850 energy transfer in LH2 by perturbing the transition density of the B850 as shown by ab initio calculations on a supermolecule of two B850 BChls, one carotenoid and one B800 BChl. Further calculations on dimers of B850 BChl estimate the intra- and interpolypeptide coupling to be 315 and 245 cm^{-1}, respectively. These interactions are dominated by Coulombic coupling, while the orbital overlap dependent coupling is ~20% of the total. Photon echo peak shift experiments (3PEPS) on LH1 and the B820 subunit are quantitatively simulated with identical parameters aside from an energy transfer time of 90 fs in LH1 and ∞ in B820, suggesting that excitation is delocalized over roughly two pigments in LH1. 3PEPS data taken at room and low temperature (34 K) on the B800-B820 suggest that static disorder is the dominant mechanism localizing excitation in LH1 and LH2. We suggest that the competition between the delocalizing effects of strong electronic coupling and the localizing effects of disorder and nuclear motion results in excitation in the B850 and B875 rings being localized on 2-4 pigments within approximately 60 fs.

10

On the Time Dependent Features of the Two-Colour Light Pulses Propagation in the Sodium Vapour

80%

Alhasan A., Fiutak J.

Acta Physica Polonica A

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2006

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vol. 109

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issue 2

143-157

EN

The phase and group velocities of the pulsed light are suitably defined and calculated. So are the duration of both pulses, probe and coupling, and their energies as a function of the travelled distance. The time evolution, for a given distance, of the dressed atom state is described by the Liouville-von Neumann equation for the density matrix.

11

Excited-State Equilibration and the Fluorescence-Absorption Ratio

80%

Knox R.

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vol. 95

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issue 1

85-103

EN

In any complex system at temperature T the absorption cross-section and fluorescent power at a given photon energy are connected by a simple relation if the system is in thermal equilibrium while occupying one particular electronic excited state. Although this situation is impossible in principle because of finite excited-state lifetimes, it is often approximated to the extent that the simple relation, which is expressed as a linear function of energy with slope -1/k_{B}T, holds in a variety of cases. (The usual symbols for Boltzmann's constant and absolute temperature are used.) Observed deviations are of two principal kinds: a slope characteristic of some temperature T* other than ambient, and departures from a single pure straight line. The latter may include seemingly random variations and in some cases multiple regions of straight-line behavior. We have recently introduced an effective temperature T*(E), derived from the actual local slope of the putative straight line at energy E, which turns out to be a very sensitive detector of deviations from the ideal and, we believe, from equilibrium in the excited state. Plots of T*(E) display a variety of features. An anomaly in the T*(E) spectrum of chlorophyll a can be analyzed on this model, indicating a second weakly fluorescent state about 70 meV below the well-known Q_{y} band. The cases of chlorophyll and many others are included in a selective review of applications of the universal relation to fluorescent systems.

12

Effective Velocity of Soliton in the Presence of a Periodic Background

80%

Pełka J., Zagrodziński J.

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EN

The effective soliton velocity in the presence of a periodic background differs from that when a soliton propagates alone. Using approximate relations for the Riemann-theta functions, the effective soliton velocity is derived and discussed. General relations are illustrated by examples of Korteweg de Vries and sine-Gordon equations because of the application in the Josephson junction theory.

13

An Iterative Method for Extreme Optics of Two-Level Systems

80%

Parzyński R., Sobczak M., Plucińska A.

Acta Physica Polonica A

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2004

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vol. 106

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issue 6

827-842

EN

We formulate the problem of a two-level system in a linearly polarized laser field in terms of a nonlinear Riccati-type differential equation and solve the equation analytically in time intervals much shorter than half the optical period. The analytical solutions for subsequent intervals are then stuck together in an iterative procedure to cover the whole scale time of the laser pulse. Very good quality of the iterative method is shown by recovering with it a number of subtle effects met in earlier numerically calculated photon-emission spectra from model molecular ions, double quantum wells, atoms, and semiconductors. The method is used to describe novel, carrier-envelope offset phase effects in the region of extreme nonlinear optics, i.e., when two-level systems are exposed to pulses of only a few cycles in duration and strength ensuring the Rabi frequency to approach the laser light frequence.

14

Coherent Manipulations in Semiconductor Nanostructures

61%

Amand T., Marie X., Renucci P., Vanelle E.

|

EN

This contribution presents recent results on spin manipulation by optical pulses in various semiconductor nanostructures such as quantum wells, microcavities, quantum dots. The potentialities of temporal coherent control, as well as spin dynamics under magnetic field are investigated, using the current ultrafast emission spectroscopy techniques.

Refine search results

Quantum Optics of Atomic Wave-Packets

On the q-Analogue of a Black Body Radiation

Phonon Effects on Population Inversion in Quantum Dots: Resonant, Detuned and Frequency-Swept Excitations

Ultrafast Coherent Control of Spin Precession Motion by Terahertz Magnetic Pulses

Binding of Biexcitons in GaAs/AlGaAs Superlattices

Ultrafast Phenomena in II-VI Semiconductors

Investigation of Radiation Trapping in Atomic Vapour Excited by Weak Resonant Laser Pulses

Extreme Nonlinear Optics in Terms of Riccati-Type Equation

The Light Harvesting Process in Purple Bacteria

On the Time Dependent Features of the Two-Colour Light Pulses Propagation in the Sodium Vapour

Excited-State Equilibration and the Fluorescence-Absorption Ratio

Effective Velocity of Soliton in the Presence of a Periodic Background

An Iterative Method for Extreme Optics of Two-Level Systems

Coherent Manipulations in Semiconductor Nanostructures