Enhanced Third-Order Nonlinearity in Semiconductors Giving Rise to 1 THz Radiation

Third harmonic generation (THG) efficiency is shown to be a greatly enhanced at the onset of inelastic scattering of electrons on optic phonons. Scaling experiments are performed on n-type InP at the pump wave frequency of 9.43 GHz at 80 K. Monte Carlo modeling is employed for scaling the effect to the 3rd harmonic frequency of 1 THz. The THG efficiency in n-type GaAs and InP as well as in the wurtzite phase of n-type InN and GaN compound crystals is compared to that in n-type Si. The efficiency maximum is found to weaken due to the quasi-elastic scattering on acoustic phonons and elastic scattering on ionized impurities. Nevertheless, the THG efficiency at 1 THz in InP crystals cooled down to liquid nitrogen temperatures is predicted to be 2 orders of magnitude higher than the reference value of 0.1% experimentally recorded up to now in n-type Si.     

Event-enhanced quantum theory and piecewise deterministic dynamics

The standard formalism of quantum theory is enhanced and definite meaning is given to the concepts of experiment, measurement and event. Within this approach one obtains a uniquely defined piecewise deterministic algorithm generating quantum jumps, classical events and histories of single quantum objects. The wave-function Monte Carlo method of Quantum Optics is generalized and promoted to the level of a fundamental process generating all the real events in Nature. The already worked out applications include SQUID-tank model and generalized cloud chamber model with GRW spontaneous localization as a particular case. Differences between the present approach and quantum measurement theories based on environment-induced master equations are stressed. Questions: what is classical, what is time, and what observers are addressed. Possible applications of the new approach are suggested, among them connection between the stochastic commutative geometry and Connes' noncommutative formulation of the Standard Model, as well as potential applications to the theory and practice of quantum computers.     

31P and 11B NMR in amorphous NiPB alloys near the paramagnetic-ferromagnetic transition

Knight-shift and nuclear spin-lattice relaxation time measurements have been performed between 4.2°K and room temperature on ¹¹B and ³¹P in amorphous NiPB alloys near the para-ferromagnetic transition. The EFG parameters on ¹¹B were found to be ν_Q=200(±20)kHz and η = 0.35 (±0.10). Knight-shift and Korringa spin-lattice relaxation are mainly due to mechanisms involving p electrons. The effect of Ni magnetic clouds results in a broadening of the linewidth. We observed also the occurence of a Giovannini-Heeger-like contribution to the spin-lattice relaxation rate.     

Local relativistic invariant flows for quantum fields

For quantum fields with trigonometric interaction in arbitrary space dimension we construct a representation of the Lorentz group by automorphisms on a Banach space generated by the Weyl algebra.     

A covariant frame to test Special Relativity including relativistic gravitation

We generalize Robertson's frame designed to discuss the experimental tests of Special Relativity. We include parametrized post-Newtonian theories of gravitation in the new frame. This generalization includes covariant equations for the motion of a test particle. We discuss the possibility of new tests such as tests of Special Relativity in astronomy.On leave from: école Polytechnique, F-91128 Palaiseau Cedex, France     

Analysis of coherent surface wave dispersion and attenuation for non-destructive testing of concrete

Rayleigh waves measurements are used to characterise cover concrete and mortar in the frequency range 60–180 kHz. At these frequencies, the wavelength is comparable to the size of the aggregates, and waves propagate in a multiple scattering regime. Acquired signals are then difficult to interpret due to an important incoherent part. The method proposed here is the study of the coherent waves, obtained by averaging signals over several configurations of disorder. Coherent waves give information on an equivalent homogeneous medium. To acquire a large amount of measurements with accuracy, an optimised piezoelectric source is used with a laser interferometer for reception. Adapted signal processing technique are presented to evaluate the coherent phase and group velocities and also the coherent attenuation parameter. The sensitivity of these three parameters with the properties of concrete is discussed, as well as the necessity to use coherent waves to obtain accurate results.     

Study of 5-azidomethyl-8-hydroxyquinoline structure by X-ray diffraction and HF–DFT computational methods

5-Azidomethyl-8-hydroxyquinoline has been synthesized and characterized using IR, ¹H and ¹³C NMR spectroscopic methods. Thermal analysis revealed no solid-solid phase transitions. The crystal structure of this compound was refined by Rietveld method from powder X-ray diffraction data at 295 K. The single- crystal structure of the compound at 260 K was solved and refined using SHELX 97 program. According to the data obtained by both methods, the structure of the compound is monoclinic, space group P2₁/c, with Z = 4 and Z' = 1. For the single crystal at 260 K, a = 12.2879 (9) Å, b = 4.8782 (3) Å, c = 15.7423 (12) Å, β=100.807(14)°. Mechanisms of deformation resulting from intra- and intermolecular interactions, such as hydrogen bonding, induced slight torsions in the crystal structure. The optimized molecular geometry of 5-azidomethyl-8-hydroxyquinoline in the ground state is calculated using density functional theory (B3LYP) and Hartree-Fock (HF) methods with the 6-311G(d,p) basis set. The calculated results show good agreement with experimental values. Energy gap of the molecule was found using HOMO and LUMO calculation which reveals that charge transfer occurs within the molecule.

     

Numerical study of ultra-short laser ablation of metals and of laser plume dynamics

Numerical modeling is used to investigate the physical mechanisms of the interaction of ultra-short (sub-picosecond) laser pulses with metallic targets. The laser–target interaction is modeled by using a one-dimensional hydrodynamic code that includes the absorption of laser radiation, the electronic heat conduction, the electron-phonon or electron–ion energy exchange, as well as a realistic equation of state. Laser fluences typical for micromachining are considered. The results of the 1D modeling are then used as the initial conditions for a 2D plasma expansion model. The dynamics of laser plume expansion in femtosecond regime is investigated. Calculations show that the plasma plume is strongly forward directed. In addition, a two-peaked axial density profile is obtained for 400 nm laser wavelength. The calculation results agree with the experimental observations. PACS 52.38.Mf; 02.60.Cb     

Giant optical anisotropy in single InAs quantum dots

We present the experimental evidence of giant optical anisotropy in single InAs QDs. Polarization-resolved photoluminescence spectroscopy in single QDs reveals a linear polarization ratio which fluctuates, from one dot to another, in sign and in magnitude with absolute values up to 82%. We do not observe any dependence of the linear polarization on incident power and temperature.