10,725 research outputs found
Improved light extraction in the bioluminescent lantern of a Photuris firefly (Lampyridae)
A common problem of light sources emitting from an homogeneous
high-refractive index medium into air is the loss of photons by total internal
reflection. Bioluminescent organisms, as well as artificial devices, have to
face this problem. It is expected that life, with its mechanisms for evolution,
would have selected appropriate optical structures to get around this problem,
at least partially. The morphology of the lantern of a specific firefly in the
genus Photuris has been examined. The optical properties of the different parts
of this lantern have been modeled, in order to determine their positive or
adverse effect with regard to the global light extraction. We conclude that the
most efficient pieces of the lantern structure are the misfit of the external
scales (which produce abrupt roughness in air) and the lowering of the
refractive index at the level of the cluster of photocytes, where the
bioluminescent production takes place.Comment: 13 pages, 11 figures, published in Optics Expres
Ultrafast nonlinear optical response of Dirac fermions in graphene
The speed of solid-state electronic devices, determined by the temporal dynamics of charge
carriers, could potentially reach unprecedented petahertz frequencies through direct
manipulation by optical fields, consisting in a million-fold increase from state-of-the-art
technology. In graphene, charge carrier manipulation is facilitated by exceptionally strong
coupling to optical fields, from which stems an important back-action of photoexcited carriers.
Here we investigate the instantaneous response of graphene to ultrafast optical fields,
elucidating the role of hot carriers on sub-100 fs timescales. The measured nonlinear
response and its dependence on interaction time and field polarization reveal the back-action
of hot carriers over timescales commensurate with the optical field. An intuitive picture is
given for the carrier trajectories in response to the optical-field polarization state. We note
that the peculiar interplay between optical fields and charge carriers in graphene may also
apply to surface states in topological insulators with similar Dirac cone dispersion relations.Peer ReviewedPostprint (published version
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