Femtosecond photon echo in dye-doped polymer films at room temperature

The signals of primary and stimulated femtosecond photon echo in polymer films doped with dye (phthalocyanine) molecules have been experimentally investigated at room temperature. A femtosecond echo spectrometer for these echo experiments is described. The decay curves of echo signals with increasing time intervals between excitation femtosecond pulses are obtained and blue shifts of the spectra of femtosecond echo signals with respect to the spectrum of excitation pulses are revealed. The possibilities of using the studied doped polymer films as recording media for high-temperature echo processors and coolants in optical refrigerators are analyzed. © Allerton Press, Inc. 2008

DYNAMIC ECHO-HOLOGRAM TRANSFORMATION IN THREE-LEVEL SYSTEMS.

Dynamic echo holography is a new field where photon (light) echo signals are used. Under certain conditions, information contained in the wave front of excited pulses can be reproduced in the wave front of echo signals. The peculiarities of hologram formation in three-level systems are investigated. Transformation of the real time scale and the events order reversion are possible in stimulated echo hologram recording

Photon echo as a method of a spectroscopy of molecular Iodine vapors in cooling supersonic molecular jets

The article is devoted to photon echo detection in molecular iodine vapors cooled under supersonic jets. This phenomena could be used in spectroscopic diagnosis of the jets. The methodic, results and the possibilities of their practical application in the development of the optical echo-processors are discussed

Boson operator elimination method in the laser cooling of solids

We use Bogoliubov's boson variabies elimination method to investigate the laser cooling of solid samples. We derive an exact kinetic equation for the quantum description of the laser cooling of glasses and crystals doped by rare-earth ions and find its stationary solution. We estimate the temperature of a laser-cooled glass doped by three-valence ytterbium

Sputtering of Indium under polyatomic ion bombardment

The main goal of the present study is the investigation of the sputtering of neutral particles from a metal surface under atomic and polyatomic ion bombardment using secondary neutral time-of-flight mass spectrometry (ToF SNMS). For postionization of neutral species, UV laser irradiation with wavelength 193 nm was utilized. For generation of polyatomic projectiles, a negative sputter cesium ion source suitable for ToF SNMS setup was developed and built. The ion source delivers negatively charged (m=1÷5) and polyatomic ions produced from a gold sputter target bombarded by positive Cs−mAu2AuCs+ ions. Mass separation of primary projectiles in the ion source is performed by a built-in compact Wien filter allowing to separate heavy ions in the energy range of several keV. In the experiment, an indium surface was bombarded by (m=1÷5) projectiles with total impact energy of 5 and 10 keV. The obtained mass distributions of sputtered indium species reveal that the partial yields of sputtered clusters increase under polyatomic ion bombardment. It is shown that the enhancement in total sputtering yield per constituent atom of the projectile ion is non-additively enhanced in the case of diatomic ion bombardment in comparison with monoatomic projectile ions impinging at the same velocity. The enhancement of partial yields observed for sputtered clusters is found to increase with increasing cluster size, reaching a factor of several ten for the largest detected cluster. −mAu Apart from sputtering yields, kinetic energy distributions (KED) of sputtered neutral indium atoms ejected under mono- and polyatomic projectile ion bombardment were measured. It is shown that In monomers sputtered by monoatomic projectiles with an impact energy of 5 keV are emitted mostly from linear collision cascades. At higher kinetic energy, or polyatomic projectile impact, it is revealed that in addition to the atoms sputtered from the linear cascade, a low energetic contribution of atoms sputtered from a collisional spike appears. This contribution in the KED increases with increasing impact energy and nuclearity of projectile. In the case of 10-keV projectiles, the sputtering process is shown to be dominated by the spike contribution. By subtracting the linear cascade contribution from the measured KED, the pure emission energy spectrum produced by the collisional spike is identified. It is found that the most probable emission energy of atoms emitted from the spike is more than one order of magnitude lower in comparison with the surface binding energy of indium. The obtained KED of indium monomers emitted from the spike were interpreted in terms of published theoretical models of the sputtering process from a spike. It is shown that the obtained data cannot be explained in terms of a thermal spike model. The obtained results are shown to agree more favorably with a thermodynamic gas flow model describing the particle emission process as a quasi-free expansion of a superheated near-surface volume. −1Au−3Au By comparing the partial sputtering yields of emitted secondary ions and their neutral counterparts, the ionization probabilities of indium atoms sputtered by atomic and polyatomic projectiles were measured. It is revealed that ionization probabilities of sputtered In monomers decrease when polyatomic projectiles are utilized. Data of this kind are of great interest both from a fundamental perspective and for practical applications of Secondary Ion Mass Spectrometry (SIMS) in surface analysis. The measured data are interpreted in terms of published theories of secondary ion formation. Our results indicate that the electronic excitation of the solid induced by the projectile impact decrease with increasing projectile nuclearity, a finding which reveals an opposite trend to that observed for the sputter yields. This surprising result cannot be understood in terms of published theory and has therefore motivated an ongoing study in our group to model excitation and ionization processes in the frame of a molecular dynamics computer simulation of sputtering process

Suppression of spin-state transition in epitaxially strained LaCoO_{3}

Epitaxial thin films of LaCoO_{3} (E-LCO) exhibit ferromagnetic order with a transition temperature T_c = 85 K, while polycrystalline thin LaCoO_{3} films (P-LCO) remain paramagnetic. The temperature-dependent spin-state structure for both E-LCO and P-LCO was studied by x-ray absorption spectroscopy at the Co L_{2,3} and O K edges. Considerable spectral redistributions over temperature are observed for P-LCO. The spectra for E-LCO, on the other hand, do not show any significant changes for temperatures between 30 K and 450 K at both edges, indicating that the spin state remains constant and that the epitaxial strain inhibits any population of the low-spin (S = 0) state with decreasing temperature. This observation identifies an important prerequisite for ferromagnetism in E-LCO thin films.Comment: 5 pages, 5 figures, submitted to Physical Review