Temperature dependences of the electron-phonon coupling, electron heat capacity and thermal conductivity in Ni under femtosecond laser irradiation

The electron temperature dependences of the electron-phonon coupling factor, electron heat capacity and thermal conductivity are investigated for Ni in a range of temperatures typically realized in femtosecond laser material processing applications, from room temperature up to temperatures of the order of 10⁴ K. The analysis is based on the electronic density of states obtained through the electronic structure calculations. Thermal excitation of d band electrons is found to result in a significant decrease in the strength of the electron-phonon coupling, as well as large deviations of the electron heat capacity and the electron thermal conductivity from the commonly used linear temperature dependences on the electron temperature. Results of the simulations performed with the two-temperature model demonstrate that the temperature dependence of the thermophysical parameters accounting for the thermal excitation of d band electrons leads to higher maximum lattice and electron temperatures achieved at the surface of an irradiated Ni target and brings the threshold fluences for surface melting closer to the experimentally measured values as compared to the predictions obtained with commonly used approximations of the thermophysical parameters.     

Coherent phonon excitation in bismuth

Ultrafast time-resolved reflectivity of a bismuth thin film evaporated on a silicon substrate is measured to investigate coherent phonons in bismuth. The reflectivity result is analyzed by a linear chirp approximation to obtain the time dependent frequencies of coherent phonons. Not only the optical modes are detected, which are generated by a combination of impulsive stimulated Raman scattering and displacive excitation of coherent phonon, acoustic phonon modes are also observed, which are emitted by the A_1g optical phonon.     

Quantum diffusion in polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate quantum diffusion of an electron in a model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with fluctuation of the parameters due to the impact of colored noise. The randomness is introduced by fluctuations of distance between two consecutive bases along the stacked base pairs. We demonstrate that in the model the decay time of the correlation can control the spread of the electronic wavepacket. Furthermore it is shown that in a motional narrowing regime the averaging over fluctuation causes ballistic propagation of the wavepacket, and in the adiabatic regime the electronic states are affected by localization.     

Shape evolution in <Superscript>76,78</Superscript>Kr nuclei at high spins in tilted axis cranking Hartree-Fock-Bogoliubov approach

A two-dimensional tilted axis cranking Hartree-Fock-Bogoliubov (CHFB) calculation is performed for ⁷⁶Kr and ⁷⁸Kr nuclei up to high spins J = 30 employing a pairing-plus-quadrupole (PPQ) model interaction Hamiltonian. Intricate details of the evolution of single particle structures and shapes as a function of spin have been investigated. The results show the existence of energy levels with high K quantum numbers lying close to the yrast line in both the nuclei. Such high K states should exhibit isomeric characteristics due to the K-selection rules for the γ-decays. Moreover, in ⁷⁸Kr a new band with J = 20–30 lying below the observed ground band is predicted.      

Tunable grating-assisted surface plasmon resonance by use of nano-polymer dispersed liquid crystal electro-optical material

This paper reports on the experimental observation of the displacement of a surface plasmon resonance (SPR) excited by a metallic diffraction grating. This effect is achieved by the use of an electro-optical material composed of nano-sized droplets of liquid crystals dispersed in a host polymer. The average refractive index of this material in the form of a thin film on the undulated metal surface can be modified with the application of an external electric field and to tune the wavelength at which the SPR excitation leads to a reflection minimum. The theoretical design and experimental demonstration of the principle of this component are described.     

Characterization of a high efficiency, ultrashort pulse shaper incorporating a reflective 4096-element spatial light modulator

We demonstrate pulse shaping via arbitrary phase modulation with a reflective, 1 × 4096 element, liquid crystal spatial light modulator (SLM). The unique construction of this device provides a very high efficiency when the device is used for phase modulation only in a prism based pulse shaper, namely 85%. We also present a single shot characterization of the SLM in the spatial domain and a single shot characterization of the pulse shaper in the spectral domain. These characterization methods provide a detailed picture of how the SLM modifies the spectral phase of an ultrashort pulse.     

2H( 3He, t)2p reaction at 2 GeV

The exclusive ²H( ³He, t)2p reaction has been studied at 2 GeV for energy transfers up to 500 MeV and triton angles up to 3.4^°. The protons were measured in the large acceptance magnetic detector DIOGENE, in coincidence with the forward tritons detected in a dedicated magnetic arm. The energy transfer spectra extend well above the pion threshold. However, in the region of Δ excitation, the yield is less than 10% of the inclusive ²H( ³He, t) cross-section, which indicates the small contribution of the ΔN ↦ NN process. The angular distributions of the two protons in their center of mass have been analysed as a function of energy transfer and triton angle and a Legendre polynomial decomposition has been achieved. These data have been compared to a model based on a coupled-channel approach for describing the NN and NΔ systems. Received: 21 October 2002 / Accepted: 15 November 2002 / Published online: 11 March 2003 RID="a" ID="a"e-mail: ramstein@ipno.in2p3.fr RID="†" ID="†"Deceased. RID="†" ID="†"Deceased. RID="d" ID="d"Present adress: School of Engineering, J?nk?ping University, P.O. Box 1026, S-551 11 J?nk?ping, Sweden. Communicated by M. Gar?on     

Localization properties of electronic states in a polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate localization properties of electronic states in a static model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with realistic parameters obtained by quantum-chemical calculation. The randomness in the on-site energies caused by the electron-phonon coupling is completely correlated to the off-diagonal parts. In the single electron model, the effect of the hydrogen-bond stretchings, the twist angles between the base pairs and the finite system size effects on the energy dependence of the localization length and on the Lyapunov exponent are given. The localization length is reduced by the influence of the fluctuations in the hydrogen bond stretchings. It is also shown that the helical twist angle affects the localization length in the poly(dG)-poly(dC) DNA polymer more strongly than in the poly(dA)-poly(dT) one. Furthermore, we show resonance structures in the energy dependence of the localization length when the system size is relatively small.     

Molecular beam deflection experiments on mixed clusters

Gas phase Ti-C₆₀ clusters are studied by molecular beam electric deflection. The permanent dipole moment of the TiC₆₀ molecule is determined. It is equal to 8.1±1.5 D. This dipole is due to a transfer of electron from the transition metal atom to the C₆₀ cage. No dipole is observed for Ti(C₆₀)₂ molecules. This is in agreement with the symmetrical dumbbell-like structure that has been previously proposed. Received 22 November 2000     

Meßeinrichtung zur Bestimmung niedriger 85Kr-Aktivitäten in Gasproben

Für einen speziellen technischen Anwendungszweck, bei welchem ⁸⁵Kr-Konzentrationen von weniger als 10^?5 μCi/cm³ in Gasproben von 40 Ncm³ nachzuweisen sind, wurde eine Meβeinrichtung konzipiert und aufgebaut. Sie besteht aus einem nichtselbstlöschenden Auslösezählrohr, in welchem die Gasprobe selbst als Zählgas fungiert, und den zugehörigen elektrischen Betriebsmitteln.

Charakteristische Daten sind die Meβempfindlichkeit k = 0,8 und der Nulleffekt z₀ = 92 min^?1.