Search results for "waves"
showing 10 items of 1766 documents
Even harmonics generation of high frequency radiation in current-carrying plasmas
2005
Generation of high frequency radiation harmonics in a current-carrying plasma is studied. The physical mechanism responsible for harmonics generation is provided by electron-ion collisions. The current in the plasma is sustained by a constant electric field. It is shown that the electron distribution function anisotropy due to the static field yields generation of even harmonics. As a result, the radiation spectrum emitted by the current-carrying plasma contains both even and odd harmonics, the latter being attributed to currentless plasma. For a broad range of plasma and high frequency radiation parameters, a detailed analysis of the even harmonics properties is reported.
Talbot array illuminators with binary phase gratings
2009
We establish that, in six different cases, binary phase gratings can be applied to implement Talbot array illuminators. Three of the six cases are reported for what is to our knowledge the first time.
Bidirectional Nonorthogonal Schardin-Lau Interferometer
1990
We discuss the formation of self-images of a 2-D grating composed by two rulings of equal period, but in-plane rotated. We describe the in-register condition for setting the lensless Lau effect, with this type of gratings; and we propose to use the above configuration for interferometrically visualizing, in noncoherent light, phase structures, in two nonorthogonal directions.
A method of evaluation of measured light intensities and degrees of polarization of a unit volume of turbid air
1965
In order to interpret scattered light measurements a comparison with theoretical values is necessary. It is demonstrated by means of an example the possibility to obtain a first view on the measurement results. From calculated values of various aerosol size distribution models as well as from measurements were computed: 1) the angular quotients of scattered light intensity (i.e., quotients of intensity at two scattering angles and the same wavelength) and 2) the wavelength quotients (i.e., quotients of intensity at two wavelengths and the same scattering angle). The comparison between measured and theoretical values informs us of the exponent of the aerosol size distribution and its boundar…
Poincaré sphere analysis of a ferroelectric liquid crystal optical modulator: application to optimize the contrast ratio
2008
The Poincare sphere representation is used to analyze the polarization transformation achieved with a ferroelectric liquid crystal (FLC) optical modulator. This device acts as a switchable wave-plate, in which the orientation of the principal axes rotates under the action of an applied bipolar voltage. In the standard operational mode for intensity switching, the rotation angle of the principal axes is �θ = π/4 and the phase shift is φ = π (half-wave-plate). However, for wavelengths different from the design one, the FLC deviates from the half-wave-plate performance and the optical contrast is diminished. We use the Poincare sphere representation to perform a theoretical analysis of the int…
Multiphoton One-step Ionization of Helium at 1064 nm
1989
Abstract The multiphoton ionization of helium by a strong radiation field having a wavelength of 1064 nm and a field intensity up to 5 × 1014 W cm −2 is considered within a non-perturbative treatment partially accounting for the electron-electron correlations in the initial bound state and approximately for the Coulomb interaction between the residual ion and the ejected electron in the final state. Only single-electron transitions are considered, the main emphasis being on the field polarization effects. The obtained results are compared with the few results available in the literature in the same regime as well as with very recent experimental findings. In particular, the calculated photo…
High-Energy pulse profile of the Transient X-ray Pulsar SAX J2103.5+4545
2005
In two recent INTEGRAL papers, Lutovinov et al. (2003) and Blay et al. (2004) report a timing and spectral analysis of the transient Be/X-ray pulsar SAX J2103.5+4545 at high energies (5--200 keV). In this work we present for the first time a study of the pulse profile at energies above 20 keV using INTEGRAL data. The spin-pulse profile shows a prominent (with a duty cycle of 14%) and broad (with a FWHM of ~ 51 s) peak and a secondary peak which becomes more evident above 20 keV. The pulsed fraction increases with energy from ~ 45% at 5--40 keV to ~ 80% at 40--80 keV. The morphology of the pulse profile also changes as a function of energy, consistent with variations in the spectral componen…
Relativistic transport equations with generalized mass shell constraints
1999
We reexamine the derivation of relativistic transport equations for fermions when conserving the most general spinor structure of the interaction and Green function. Such an extension of the formalism is needed when dealing with {\it e.g.} spin-polarized nuclear matter or non-parity conserving interactions. It is shown that some earlier derivations can lead to an incomplete description of the evolution of the system even in the case of parity-conserving, spin-saturated systems. The concepts of kinetic equation and mass shell condition have to be extended, in particular both of them acquire a non trivial spinor structure which describe a rich polarization dynamics.
Stable control of pulse speed in parametric three-wave solitons.
2006
International audience; We analyze the control of the propagation speed of three wave packets interacting in a medium with quadratic nonlinearity and dispersion. We find analytical expressions for mutually trapped pulses with a common velocity in the form of a three-parameter family of solutions of the three-wave resonant interaction. The stability of these novel parametric solitons is simply related to the value of their common group velocity.
Optical rogue waves and localized structures in nonlinear fiber optics
2011
We review our recent work in the field of optical rogue wave physics. Beginning from a brief survey of the well-known instabilities in optical fiber, we trace the links to recent developments in studying the emergence of high contrast localized breather structures in both spontaneous and induced nonlinear instabilities.