5,565 research outputs found
Long-range correlation of thermal radiation
A general theory is presented for the spatial correlations in the intensity
of the radiation emitted by a random medium in thermal equilibrium. We find
that a non-zero correlation persists over distances large compared to the
transverse coherence length of the thermal radiation. This long-range
correlation vanishes in the limit of an ideal black body. We analyze two types
of systems (a disordered waveguide and an optical cavity with chaotic
scattering) where it should be observable.Comment: 4 pages, 3 figure
Photon shot noise
A recent theory is reviewed for the shot noise of coherent radiation
propagating through a random medium. The Fano factor P/I (the ratio of the
noise power and the mean transmitted current) is related to the scattering
matrix of the medium. This is the optical analogue of Buttiker's formula for
electronic shot noise. Scattering by itself has no effect on the Fano factor,
which remains equal to 1 (as for a Poisson process). Absorption and
amplification both increase the Fano factor above the Poisson value. For strong
absorption P/I has the universal limit 1+3f/2 with f the Bose-Einstein function
at the frequency of the incident radiation. This is the optical analogue of the
one-third reduction factor of electronic shot noise in diffusive conductors. In
the amplifying case the Fano factor diverges at the laser threshold, while the
signal-to-noise ratio I^2/P reaches a finite, universal limit.Comment: 11 pages, 4 figures (caption to figure 3 corrected
Excess noise for coherent radiation propagating through amplifying random media
A general theory is presented for the photodetection statistics of coherent
radiation that has been amplified by a disordered medium. The beating of the
coherent radiation with the spontaneous emission increases the noise above the
shot-noise level. The excess noise is expressed in terms of the transmission
and reflection matrices of the medium, and evaluated using the methods of
random-matrix theory. Inter-mode scattering between propagating modes
increases the noise figure by up to a factor of , as one approaches the
laser threshold. Results are contrasted with those for an absorbing medium.Comment: 8 pages, 6 figure
Predictability of stock returns using financial statement information: Evidence on semi-strong efficiency of emerging Greek stock market
This article examines the predictability of stock returns in the Athens Stock
Exchange (ASE) during 1993 to 2006 by using accounting information. Using panel
data analysis, this article concludes that the selected set of financial ratios
contains significant information for predicting the cross-section of stock
returns. Results indicate that portfolios selected on the basis of financial
ratios produce higher than average returns, suggesting that the emerging Greek
market does not fully incorporate accounting information into stock prices and
hence it is not semi-strong efficient
Frequency dependence of the photonic noise spectrum in an absorbing or amplifying diffusive medium
A theory is presented for the frequency dependence of the power spectrum of
photon current fluctuations originating from a disordered medium. Both the
cases of an absorbing medium (``grey body'') and of an amplifying medium
(``random laser'') are considered in a waveguide geometry. The semiclassical
approach (based on a Boltzmann-Langevin equation) is shown to be in complete
agreement with a fully quantum mechanical theory, provided that the effects of
wave localization can be neglected. The width of the peak in the power spectrum
around zero frequency is much smaller than the inverse coherence time,
characteristic for black-body radiation. Simple expressions for the shape of
this peak are obtained, in the absorbing case, for waveguide lengths large
compared to the absorption length, and, in the amplifying case, close to the
laser threshold.Comment: 17 pages, 6 figure
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