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1
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Phonon Effects on Population Inversion in Quantum Dots: Resonant, Detuned and Frequency-Swept Excitations

100%
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.
2
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Time Resolved Photoluminescence Study of the Wide (Cd,Mn)Te/(Cd,Mg)Te Quantum Well

100%
Kutrowska J., Bugajny P., Baranowski M., Bryja L., Syperek M., Wójs A., Misiewicz J., Wiater M., Karczewski G.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
895-897
EN
The static and dynamic properties of excitons and trions in a 80 nm wide Cd_{1-x}Mn_xTe/Cd_{0.7}Mg_{0.3}Te quantum well with extremely small Mn content (x=0.00027) have been studied by means of time-integrated and time-resolved photoluminescence experiment at low and elevated temperatures. The trion binding energy has been estimated to be 2.6 ± 0.8 meV. The exciton and trion lifetimes have been measured to be ≈ 150 ps, and ≈ 200 ps, respectively. The temperature dependence of both lifetimes together with the multicomponent character of the PL decay process suggest a spatial localization of excitons and trions in the investigated quantum well.
3
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White Light Snapshot of Non-Equilibrium High-Spin State in a Molecular Crystal

100%
Kaszub W., Collet E., Cailleau H., Servol M., Boillot M., Tissot A., Lorenc M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
324-327
EN
The spin-crossover compound [(TPA)Fe(TCC)]PF_6 was experimentally investigated using time-resolved optical pump and supercontinuum probe technique. Changes of VIS optical density at thermal equilibrium of a crystal with different high-spin/low-spin fractions are compared to changes recorded picoseconds after femtosecond laser excitation. A white light snapshot of the high-spin state at 180 K is extracted from time-resolved spectra. Our results indicate that the temperature of the electronic state affects the absorption spectra of high- and low-spin states.
4
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Light-Induced Precession of Magnetization in Ferromagnetic Semiconductor (Ga,Mn)As

100%
Tesařová N., Němec P., Rozkotová E., Trojánek F., Malý P.
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issue 5
1065-1066
EN
Precession of magnetization induced by laser pulses in (Ga,Mn)As was studied by the pump-and-probe technique. We concentrated on various experimental aspects that can be used to identify a part of the measured magneto-optical signals that provides information about the dynamics of magnetization. We also revealed that that it takes about 80 ps before the quasi-equilibrium precession of magnetization is initiated by the impact of laser pulse.
5
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Photoinduced Ionic to Neutral Phase Transition in TTF-CA Studied by Time-Resolved Infrared Vibrational Spectroscopy

100%
Matsubara Y., Yoshida T., Ishikawa T., Okimoto Y., Koshihara S., Onda K.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
340-342
EN
We studied the photoinduced ionic to neutral phase transition in tetrathiafulvalene-p-chloranil (TTF-CA) using time-resolved infrared vibrational spectroscopy. By monitoring the charge sensitive b_{1u} ν_{10} band of CA after photoexcitation by a 1.55 eV pulse, we found that the photoinduced N-phase has the same charge of the N-phase in thermal equilibrium and there is no charge variation during the photoinduced phase transition. We also found that the photoinduced N-phase grows through at least two steps over 300 ps.
6
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PIPT from the Beginning to Future

100%
Cailleau H., Luty T., Koshihara S., Servol M., Lorenc M., Buron-Le Cointe M., Collet E.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
297-306
EN
The birth of the field of photoinduced phase transitions was strongly influenced by the conceptual viewpoint expressed by Professor Y. Toyozawa on the condensation of relaxed excitons. Since this first period, twenty years ago, this young field has been expanding rapidly along a diversity of directions. Nowadays, it goes hand in hand with the challenges of today's science: emergence, nonlinearity, coherence, far away from equilibrium, for example. The control of the functionality of a material via photoexcited states poses many new fundamental questions. Some of them will be overviewed: (i) the nature of the control parameters and the nature of the relevant collective variables, especially the order parameters, which characterize the evolution of the system, (ii) the difference between photoinduced transformations under continuous light irradiation and those resulting from an ultrashort laser pulse, (iii) the physical mechanisms of ultrafast photoinduced phase transitions from the formation and proliferation of phototransformed entities to the softening of a collective mode.
7
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Spectral Dependence of Fluorescence Enhancement in LH2-Au Nanoparticle Hybrid Nanostructures

100%
Bujak L., Brotosudarmo T., Czechowski N., Olejnik M., Ciszak K., Litvin R., Cogdell R., Heiss W., Mackowski S.
Acta Physica Polonica A
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2012
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vol. 122
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issue 2
252-254
EN
We report on the influence of plasmon resonance in spherical gold nanoparticles on the optical properties of light-harvesting complex LH2 from the purple bacteria Rhodopseudomonas palustris. Systematic studies as a function of the excitation energy and the separation distance indicate that metal enhanced fluorescence shows strong dependence upon both of these parameters. We observe substantial increase of the fluorescence from LH2 complex in a hybrid nanostructure with 12 nm silica spacer. On the other hand, the enhancement measured with laser tuned into the plasmon resonance is almost threefold compared to the off-resonance configuration. The enhancement of fluorescence intensity originates in both cases from the increase of carotenoid absorption in the LH2 complex.
8
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Lattice Dynamics of Laser Excited Ferroelectric BaTiO_3

88%
Issenmann D., Schleef S., Ibrahimkutty S., Buth G., Baumbach T., Plech A., Beyer M., Demsar J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
319-323
EN
We investigated the lattice dynamics of the prototypic ferroelectric barium titanate close to its ferroelectric-paraelectric phase transition aiming at a better understanding of the atomistic nature of the transition. The usage of time-resolved X-ray techniques allows to disentangle lattice motion and unit cell changes, which, in part, relate to the ferroelectric polarization. In the quasi-static case both the electrical and the laser excitation show a mean-field, simple thermal behaviour, while for time scales shorter than nanoseconds the impulsive nature of the excitation becomes visible.
9
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Slow Dynamics of the Photoinduced Phase Transition in Pd(dmit)_2 Salts (dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

88%
Ishikawa T., Tanaka T., Fukazawa N., Matsubara Y., Okimoto Y., Onda K., Koshihara S., Tamura M., Kato R.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2B
316-318
EN
Slow dynamics of the initially photoinduced state has been observed by the pump-probe type time-resolved reflection spectroscopy in the charge separated phase of the half-filled strong dimer system, Et_2Me_2Sb[Pd(dmit)_2]_2 (dmit = 1,3-dithiol-2-thione-4,5-dithiolate). We have succeeded to reproduce the probe photon energy dependence of the time profile qualitatively in the time delay range from 10 ps to 1 ns assuming the dynamical expansion of the domain of the photo-induced dimer-Mott insulating phase in the host charge-separated one.
10
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Room Temperature Carrier Kinetics in the W-type GaInAsSb/InAs/AlSb Quantum Well Structure Emitting in Mid-Infrared Spectral Range

75%
Syperek M., Ryczko K., Dallner M., Dyksik M., Motyka M., Kamp M., Höfling S., Misiewicz J., Sęk G.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1224-1228
EN
Room temperature carrier kinetics has been investigated in the type-II W-design AlSb/InAs/Ga_{0.80}In_{0.20}As_{0.15}Sb_{0.85}/InAs/AlSb quantum well emitting in the mid-infrared spectral range (at 2.54 μ m). A time-resolved reflectance technique, employing the non-degenerated pump-probe scheme, has been used as a main experimental tool. Based on that, a primary carrier relaxation time of 2.3±0.2 ps has been found, and attributed to the initial carrier cooling process within the quantum well states, while going towards the ground state via the carrier-optical phonon scattering mechanism. The decay of a quasi-equilibrium carrier population at the quantum well ground states is primarily governed by two relaxation channels: (i) radiative recombination within distribution of spatially separated electrons and holes that occurs in the nanosecond time scale, and (ii) the hole tunnelling out of its confining potential, characterized by a 240±10 ps time constant.
11
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Positron Annihilation in MnFe_2O_4/MCM-41 Nanocomposite

75%
Wiertel M., Surowiec Z., Gac W., Budzyński M.
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vol. 125
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issue 3
793-797
EN
In the paper results of studies of MnFe_2O_4/MCM-41 nanocomposites have been presented. The influence of manganese ferrite loading on changes of porous properties of mesoporous MCM-41 structure was studied by means of N_2 sorption/desorption method and positron annihilation lifetime spectroscopy. Disappearance of the longest-lived ortho-positronium component (τ_5) of pure MCM-41 mesoporous material in the positron annihilation lifetime spectra of MnFe_2O_4/MCM-41 measured in vacuum is a result of either o-Ps quenching or the Ps inhibition mechanism. Filling of pores in the studied nanocomposites by air at ambient pressure causes partial reappearance of the (τ_5) component except for the sample with maximum ferrite content. Both the (τ_5) component lifetime and intensity are suppressed together with increasing MnFe_2O_4 content by chemical quenching and inhibition of Ps formation occur. Observed anti-quenching effect of air is a result of two processes: neutralization of some surface active centres acting as inhibitors and considerably weaker paramagnetic quenching by O_2 molecules.
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