893 research outputs found
Spontaneous-emission rates in finite photonic crystals of plane scatterers
The concept of a plane scatterer that was developed earlier for scalar waves
is generalized so that polarization of light is included. Starting from a
Lippmann-Schwinger formalism for vector waves, we show that the Green function
has to be regularized before T-matrices can be defined in a consistent way.
After the regularization, optical modes and Green functions are determined
exactly for finite structures built up of an arbitrary number of parallel
planes, at arbitrary positions, and where each plane can have different optical
properties. The model is applied to the special case of finite crystals
consisting of regularly spaced identical planes, where analytical methods can
be taken further and only light numerical tasks remain. The formalism is used
to calculate position- and orientation-dependent spontaneous-emission rates
inside and near the finite photonic crystals. The results show that emission
rates and reflection properties can differ strongly for scalar and for vector
waves. The finite size of the crystal influences the emission rates. For
parallel dipoles close to a plane, emission into guided modes gives rise to a
peak in the frequency-dependent emission rate.Comment: 18 pages, 6 figures, to be published in Phys. Rev.
Varying the effective refractive index to measure optical transport in random media
We introduce a new approach for measuring both the effective medium and the
transport properties of light propagation in heterogeneous media. Our method
utilizes the conceptual equivalence of frequency variation with a change in the
effective index of refraction. Experimentally, we measure intensity
correlations via spectrally resolved refractive index tuning, controlling the
latter via changes in the ambient pressure. Our experimental results perfectly
match a generalized transport theory that incorporates the effective medium and
predicts a precise value for the diffusion constant. Thus, we directly confirm
the applicability of the effective medium concept in strongly scattering
materials.Comment: 5 pages, 5 figure
Analytical modeling of light transport in scattering materials with strong absorption
We have investigated the transport of light through slabs that both scatter
and strongly absorb, a situation that occurs in diverse application fields
ranging from biomedical optics, powder technology, to solid-state lighting. In
particular, we study the transport of light in the visible wavelength range
between and nm through silicone plates filled with YAG:Ce
phosphor particles, that even re-emit absorbed light at different wavelengths.
We measure the total transmission, the total reflection, and the ballistic
transmission of light through these plates. We obtain average single particle
properties namely the scattering cross-section , the absorption
cross-section , and the anisotropy factor using an analytical
approach, namely the P3 approximation to the radiative transfer equation. We
verify the extracted transport parameters using Monte-Carlo simulations of the
light transport. Our approach fully describes the light propagation in phosphor
diffuser plates that are used in white LEDs and that reveal a strong absorption
() up to , where is the
slab thickness, is the absorption mean free path. In
contrast, the widely used diffusion theory fails to describe this parameter
range. Our approach is a suitable analytical tool for industry, since it
provides a fast yet accurate determination of key transport parameters, and
since it introduces predictive power into the design process of white light
emitting diodes
Control of light transmission through opaque scattering media in space and time
We report the first experimental demonstration of combined spatial and
temporal control of light trajectories through opaque media. This control is
achieved by solely manipulating spatial degrees of freedom of the incident
wavefront. As an application, we demonstrate that the present approach is
capable to form bandwidth-limited ultrashort pulses from the otherwise randomly
transmitted light with a controllable interaction time of the pulses with the
medium. Our approach provides a new tool for fundamental studies of light
propagation in complex media and has potential for applications for coherent
control, sensing and imaging in nano- and biophotonics
Inhibited spontaneous emission of quantum dots observed in a 3D photonic band gap
We present time-resolved emission experiments of semiconductor quantum dots
in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study
is made of crystals with a range of pore radii to tune the band gap relative to
the emission frequency. The decay rates averaged over all dipole orientations
are inhibited by a factor of 10 in the photonic band gap and enhanced up to 2?
outside the gap, in agreement with theory. We discuss the effects of spatial
inhomogeneity, nonradiative decay, and transition dipole orientations on the
observed inhibition in the band gap.Comment: 5 figures, update author lis
- …