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1
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Femtosecond Reflection Spectroscopy in La_{1.5}Sr_{0.5}CoO_4

100%
Egawa T., Okimoto Y., Fukaya R., Onda K., Ishikawa T., Koshihara S., Isayama A., Sasagawa T.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
307-309
EN
Ultrafast optical response has been investigated using fs laser system on a perovskite-type cobalt oxide, La_{1.5}Sr_{0.5}CoO_4. After the photoirradiation at room temperature, the time profile of relative change of reflectance (Δ R/R) shows a sudden change within the pulse duration ( ≈ 150 fs) and decays with a lifetime of ≈ 330 fs. The sign of Δ R/R after the photoexcitation is positive in the mid-infrared region (at 0.50 eV) while negative in the visible energy region (at 2.0 eV), implying photoinduced change of the electronic structure after the photoexcitation.
2
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Investigation of Optical Nonlinearities and Carrier Dynamics in In-Rich InGaN Alloys

100%
Nargelas S., Malinauskas T., Jarasiunas K., Dimakis E., Georgakilas A.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
839-843
EN
We present experimental studies of nonequilibrium carrier dynamics in InGaN alloys with 70-90% content of In by using picosecond transient grating technique. The observed faster recombination rate in alloys with higher Ga content and formation of a thermal grating via a lattice heating, being more pronounced for layers with larger band gap, indicated that the main reason of the heating is not the excess energy of photons, but the defect density which increases with Ga content. A gradual decrease in carrier lifetime with excitation or with increasing temperature in 50-300 K range point out the role of potential barriers in carrier recombination.
3
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Role of Oxygen Coordination on the Ultrafast Demagnetization in Ferrite Nanoparticles

80%
Terrier E., Liu Y., Begin S., Pichon B., Bigot J., Halte V.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
345-346
EN
In this work, we have studied the ultrafast dynamics of charges and spins in assemblies of magnetite (Fe₃O₄) and maghemite (γ - Fe₂O₃) nanoparticles. We demonstrate that using time-resolved magneto-optics one is able to disentangle those very similar iron oxide structures. The Fe₃O₄ nanoparticles are elaborated by hydrothermal decomposition and deposited by drop on a glass substrate. γ - Fe₂O₃ nanoparticles assemblies have been obtained by annealing the Fe₃O₄ nanoparticles. Comparing time resolved transmission and Faraday rotation, our measurements show that in case of Fe₃O₄ the demagnetization occurs after the thermalization of the charges, as expected from previous works on ultrafast quenching of magnetization in ferromagnetic nanostructures. On the contrary, in the case of maghemite nanoparticles, an acceleration of the demagnetizing occurs, leading to a simultaneous charges and spins dynamics. We attribute this behavior to the rearrangement of vacancies and annealing of crystal defects in maghemite.
4
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Time-Resolved Pump-Probe Diffraction Experiment at SOLEIL Synchrotron: Photoinduced Spin Transition in the Molecular Crystal [TPA Fe(III) TCC] PF_6

80%
Laulhé C., Ravy S., Fertey P., Elkaim E., Legrand F., Féret P., Hollander P., Hustache S., Bordessoule M., Ricaud J., Collet E., Lorenc M., Buron-Le Cointe M., Cailleau H., Tissot A., Boillot M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
332-335
EN
We present the first time-resolved pump-probe experiment performed at synchrotron SOLEIL at the CRISTAL diffraction beamline. The time-resolved setup will be used in the near future for sub-ns time resolution experiments. We studied spin state switching in a [TPA Fe(III) TCC] PF_6 single crystal as induced by a ≈6 ns laser pulse (1064 nm), by measuring the 3D diffraction volume of the 002 Bragg reflection as a function of time after excitation. The intensity profiles (rocking curves) are found to evolve at two characteristic timescales, namely hundreds of ns and few μs, exhibiting subtle profile changes and peak broadenings. Consistently with previous studies, we interpret these features as due to structural inhomogeneities related to laser-induced deformation wave propagation and heat diffusion, which both start from the absorbing sites.
5
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Search for the Photo-Induced Hidden Phase in Inorganic and Organic Systems

80%
Koshihara S., Onda K., Okimoto Y., Ishikawa T.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
328-331
EN
We review the dynamical behavior of strongly electron-lattice (orbital) coupled system induced by photo-excitation of fs laser pulse. By virtue of the femtosecond (fs) spectroscopy and picosecond (ps) time-resolved X-ray diffraction measurements, we demonstrate that the photo-irradiation creates new ordered state so called as "hidden phase" which can never be realized under thermo-equilibrium condition. This exotic phase commonly plays the key role for realizing the gigantic photo-induced changes in optical properties of inorganic and organic electron-lattice strongly coupled systems.
6
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Bond-Selective Excitation and Following Displacement of Ge Atoms in GeTe/Sb_{2}Te_{3} Superlattice

80%
Makino K., Tominaga J., Kolobov A., Fons P., Hase M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
336-339
EN
Phase change random access memory devices made from chalcogenides compounds, such as Ge_{2}Sb_{2}Te_{5}, have attracted much attention because of their high-speed read-write and low power consumption capabilities. The phase change in Ge_{2}Sb_{2}Te_{5} is thought to be characterized by the displacement of Ge atoms, accompanying relaxation of surrounding Sb and Te atoms. Here we examine a new approach, that is the manipulation of Ge-Te bonds using linearly-polarized femtosecond near-infrared optical pulses. As a result, p-polarized pump pulses are found to be more effective in inducing the precursor of phase change, probably due to the atomic arrangements along the unique axis of the superlattice structure.
7
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Ultrafast Magneto-Optical and Magnetization-Induced Second Harmonic Generation Techniques for Studies of Magnetic Nanostructures

80%
Bonda A., Uba S., Uba L.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1225-1227
EN
The work concerns application of titanium-sapphire femtosecond laser oscillator with 82 MHz repetition rate at 800 nm in measurements of ultrafast magneto-optical and magnetization-induced second harmonic generation effects. Time-resolved magneto-optical Kerr effect pump-probe method was used in investigation of ultrafast precession of magnetization in Fe/Au multilayers. Magnetization precession frequency, obtained as a function of magnetic field applied, allows determining saturation magnetization and damping factor. The magnetization-induced second harmonic generation effect has been used for study of garnet films. This method allows to determine crystallographic symmetry and hysteresis loops in an external magnetic field at 2 ω laser induced frequency. The simultaneous measurements of linear and second order magneto-optical effects enable to investigate magnetic interfaces in the studied structures.
8
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Light-Induced Precession of Magnetization in Ferromagnetic Semiconductor (Ga,Mn)As

80%
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.
9
Content available remote

Novel Excitation-Density Dependence in Strongly Spin-Charge Coupled System

80%
Ohara J., Kanamori Y., Ishihara S.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
355-358
EN
Photoinduced spin-charge dynamics in strongly correlated electron systems is studied based on an extended double-exchange model. Solving a time-dependent Schrödinger equation with the Lanczos method, we trace the process of photoinduced melting of an antiferromagnetic charge order and analyze the excitation-density dependence on that. In the case of low density photoexcitation, both charge and spin orders are melted by photocarrier doping. This is interpreted with a conventional double-exchange mechanism. In the case of high density photoexcitation, however, the charge order is melted. The antiferromagnetic spin order is transiently weakened but after turnoff of the photoirradiation it recovers. This phenomenon strikingly differs from the weak photoexcitation case.
10
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Comparison of Ultrafast Photodetectors Based on N^+GaAs and LT GaAs

80%
Białous M., Mogilinski R., Wierzbicki M., Świtkowski K., Pura B.
Acta Physica Polonica A
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2011
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vol. 119
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issue 3
382-386
EN
We present investigation of a photodetector based on nitrogen-ion-implanted GaAs. Device photoresponse signal shows 1.15 ps FWHM (400 GHz, 3 dB bandwidth) with the voltage amplitude ≈ 1 mV, measured using a constructed electro-optic sampling setup with 80 fs width, 795 nm wavelength and laser pulses repetition rate of 80 MHz. Changes in the shape of electrical signal for different beam powers excitation and voltage biases have been demonstrated, compared with LT GaAs photodetector based on the same finger geometry. Using technique of X-ray diffraction and diffuse scattering analyses we have observed the decrease of lattice constant, radius of nanoclusters after implantation, respectively, and linear density dislocations increased over twice.
11
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Carrier Dynamics and Dynamic Band-Bending in Type-II ZnTe/ZnSe Quantum Dots

80%
Syperek M., Misiewicz J., Chan C., Dumcenco D., Huang Y., Chou W.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
821-823
EN
Carrier dynamics and dynamic band-bending in self-assembled ZnTe/ZnSe quantum dots have been studied by means of time-resolved photoluminescence experiment at low temperatures. The experiment reveals clearly type-II character of the confinement potential in the dot manifested in: (i) long photoluminescence decay time constant of 28-35 ns, and (ii) temporal shift of the quantum dot peak emission towards low energy following the laser pulse excitation. The magnitude of the spectral shift Δ E depends on the dot size and the power density of excitation pulse. For the dots under study and given experimental conditions Δ E ≈ 28 ÷ 42 meV.
12
Content available remote

Ultrafast Magnetization Dynamics in Epitaxial Ni-Mn-Sn Heusler Alloy Film

61%
Bonda A., Uba S., Załęski K., Dubowik J., Uba L.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
501-504
EN
The work is devoted to studies of ultrafast magnetization dynamics induced by femtosecond laser pulses in ferromagnetic Ni-Mn-Sn shape memory Heusler alloy. We studied epitaxial thin Ni_{54.3}Mn_{31.9}Sn_{13.8} film deposited on (001) MgO substrate. Spin precession in an external magnetic field was triggered and detected by the time-resolved magneto-optical Kerr effect (TRMOKE) using pump-probe technique in dual color scheme experiment. Measurements were performed as a function of magnetic field H and pulse power P. The measured TRMOKE signal is composed of oscillatory and background components, both decaying exponentially in a nanosecond time scale. The precession frequency was determined and found to be varying in the range of 1-10 GHz with H up to 3 kOe and decreasing linearly with P. The dependence of Gilbert damping parameter α on H was determined and discussed.
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