Femtosecond photon echo and four-wave mixing in dye-doped polymer films, semiconductors and heterostructures

A review of femtosecond experiments on photon echo (PE) and four-wave mixing (FWM) performed at room temperature is presented. The Weiner-Ippen technique of FWM spectroscopy is demonstrated in dye-doped polymer films (such as polyvinilbutural doped with phthalocyanine), semiconductors (CdS) and heterostructures (GaAs/AlGaAs). The experimental setup used in these experiments is described. The dephasing times are estimated and the relaxation mechanisms are discussed. © 2014 Astro Ltd

Coherent control of the molecular dynamics in a liquid by femtosecond four-pulse excitation

© 2015 Astro Ltd. The laser non-resonant excitation based on the (2 ×2) sequence of the two pairs of the pump pulses with orthogonal linear polarizations is proposed and theoretically considered for the control of the vibrational responses without or with the low amplitude of the rotational responses in a liquid. As an example, we model the optical molecular responses resulting in the optical Kerr effect transients in ortho-dichlorobenzene. Theoretical analysis shows the high efficiency of the (2 ×2) excitation scenarios for the various manipulations of the molecular responses

Implementation of double-pulse laser control in optical Kerr effect spectroscopy

Two-pulse control of time-dependent anisotropy in liquid CCl4 and CHCl3 at room temperature is implemented using femtosecond polarisation spectroscopy. Non-resonant excitation was enhanced by means of the double-pulse pump-probe technique. It is shown that by varying the delay between the exciting pulses and their relative intensity, selection of contributions of individual intramolecular modes into the recorded signal is achieved. The molecular responses were detected using the time-resolved optically heterodyne-detected optical-Kerr-effect technique. © Published under licence by IOP Publishing Ltd

Femtosecond laser control of intramolecular vibrations in a liquid

Optical control of coherent intramolecular oscillations in chloroform CHCl3 and dimethyl sulfoxide (CH 3) 3SO is attained experimentally under normal conditions by means of femtosecond polarization spectroscopy. Nonresonant excitation of the medium is accomplished by a sequence of two linearly polarized laser pulses. The state of the medium is probed by the third pulse via the optical Kerr effect. We show that control over the vibrational dynamics of molecules on a sub-picosecond scale can be achieved by varying the delay between the excitation pulses and their relative intensity. © Allerton Press, Inc., 2012

第２章 イギリスにおける医療政策決定過程

Two-pulse control of time-dependent anisotropy in liquid CCl4 and CHCl3 at room temperature is implemented using femtosecond polarisation spectroscopy. Non-resonant excitation was enhanced by means of the double-pulse pump-probe technique. It is shown that by varying the delay between the exciting pulses and their relative intensity, selection of contributions of individual intramolecular modes into the recorded signal is achieved. The molecular responses were detected using the time-resolved optically heterodyne-detected optical-Kerr-effect technique. © Published under licence by IOP Publishing Ltd

Investigation of femtosecond photon echo in dye-doped polymer film at room temperature

Signals of primary and stimulated femtosecond photon echo were found and investigated at room temperature in a polyvinyl butyral film doped with phthalocyanine molecules. The decay curve of relative intensity and the spectrum of the signal of primary femtosecond photon echo were recorded. The physical mechanism of formation of such signals in a system of impurity centers excited through the phonon wing of the optical absorption band was discussed. © 2007 by Allerton Press, Inc

Electron dynamics at GaAs-AlGaAs heterojunction studied by ultrafast spectroscopy

In this letter the electron and spin dynamics at GaAs/AlGaAs heterojunction was studied by ultrafast spectroscopy techniques (photon echo and transient grating studies). Relaxation times and diffusion coefficients of photoexcited electrons and spins were obtained using pure optical setup. The estimated spin diffusion coefficient value of 160 cm2/s is relatively high and comparable to the electron diffusion coefficient of 200 cm2/s. This feature makes GaAs/AlGaAs heterosructure a promising material for practical application in semiconductor spintronics. © Published under licence by IOP Publishing Ltd

"Entangled" free-induction decay in CdS crystal under two-photon excitation by two crossed laser beams

A new method of two-photon excitation of femtosecond signals of "entangled" free induction decay (EFID) by two crossed 790-nm laser beams in a CdS crystal at room temperature has been realized for the first time. This "entangled" (through the wave vectors) coherent response appears only in the case when the photons involved to the process of twophoton excitation of the sample belong to the different laser beams. This technique allows one to separate the EFID signal from the exciting femtosecond pulses and to vary the response wavelength by varying the angle between their wave vectors. The most optimal case occurs when the angle between the wave vectors of exciting pulses as well as the angle between each of these wave vectors and that of the response is equal to 60°. © 2012 by Astro, Ltd

Femtosecond coherent spectroscopy of four-wave mixing and photon echoes in a GaAs/AlGaAs heterostructure at room temperature

The results from experiments employing coherent femtosecond spectroscopy in a layer of two-dimensional electron gas at the boundary of the GaAs/AlGaAs heterojunction at room temperature are presented. The decay curves of primary femtosecond photon echo are obtained. The decoherence time in two-dimensional electron gas depends strongly on the power of the exciting pulse and varies from 36 to 54 fs. The dephasing time is studied for the first time as a function of the power of exciting pulses at room temperature. It is established that this dependence obeys the law T 2 ∼ N -0.22, which differs from the typical law T 2 ∼ N -1 for unscreened electron-electron interaction in semiconductor crystals. Analysis shows that electron-phonon interaction plays an important part along with electron-electron interaction. The induced spin gratings in the GaAs/AlGaAs heterostructure are studied with an eye to their possible application in spintronics. © Allerton Press, Inc., 2012

Entangled femtosecond free induction signals in a cadmium sulfide crystal at room temperature

Entangled free induction decay (EFID) femtosecond signals are experimentally observed for the first time at a wavelength of 790 nm in a cadmium sulfide (CdS) crystal in the two-photon absorption (TPA) regime upon excitation by two crossed (angle, 60°) laser beams. The sample emitted two EFID signals simul- taneously in opposite directions. The signals were diffracted by nonequilibrium electric polarization gratings induced by two laser beams in accordance with the laws of energy and momentum conservation. The possi- bility of exciting EFID signals in the three-photon absorption regime is discussed. © Allerton Press, Inc., 2012