Search results for "Physics::Optics"
showing 10 items of 1958 documents
Recycled Photons Traveling Several Millimeters in Waveguides Based on CsPbBr 3 Perovskite Nanocrystals
2021
Reabsorption and reemission of photons, or photon recycling (PR) effect, represents an outstanding mechanism to enhance the carrier and photon densities in semiconductor thin films. This work demonstrates the propagation of recycled photons over several mm by integrating a thin film of CsPbBr3 nanocrystals into a planar waveguide. An experimental set-up based on a frequency modulation spectroscopy allows to characterize the PR effect and the determination of the effective decay time of outcoupled photons. A correlation between the observed photoluminescence redshift and the increase of the effective decay time is demonstrated, which grows from 3.5 to near 9 ns in the best device. A stochast…
Ultrahigh-Q Tunable Whispering-Gallery-Mode Microresonator
2009
Typical microresonators exhibit a large frequency spacing between resonances and a limited tunability. This impedes their use in a large class of applications which require a resonance of the microcavity to coincide with a predetermined frequency. Here, we experimentally overcome this limitation with highly prolate-shaped whispering-gallery-mode "bottle microresonators" fabricated from standard optical glass fibers. Our resonators combine an ultra-high quality factor of 360 million, a small mode volume, and near lossless fibre coupling, characteristic of whispering-gallery-mode resonators, with a simple and customizable mode structure enabling full tunability.
Strong optical nonlinearities in gallium and indium selenides related to inter-valence-band transitions induced by light pulses
1997
A nonlinear optical effect is shown to occur in gallium and indium selenides at photon energies of the order of 1.5 eV. It corresponds to transitions from a lower-energy valence band to the uppermost one when a nonequilibrium degenerate hole gas is created in the latter by a laser pulse. This inter-valence-band transition is allowed by crystal symmetry. Its oscillator strength is estimated through the $f$-sum rule and turns out to be about two orders of magnitude higher than that of the fundamental transition. The intensity of this effect is stronger when the pump pulse photon energy is close to that of the inter-valence-band transition; a condition that can be fulfilled only in indium sele…
Four-wave mixing in a ring cavity
2014
We investigate a four-wave mixing process in an N interaction scheme in Rb vapor placed inside a low-finesse ring cavity. We observe strong amplification and generation of a probe signal, circulating in the cavity, in the presence of two strong optical pump fields. We study the variations in probe field gain and dispersion as functions of experimental parameters with an eye on potential application of such a system for enhanced rotation measurements. A density-matrix calculation is performed to model the system, and the theoretical results are compared to those of the experiment.
Near-field observation of evanescent light wave coupling in subwavelength optical waveguides
2002
International audience; We report the observation, in the range of visible frequencies, of the coupling of light into integrated waveguides of subwavelength cross-sections together with a subwavelength detection at the output, of such guides. Coupling in is produced by controlling the focusing of a laser beam totally reflected at the surface of the sample. Several tens of micrometres long dielectric ridges have been efficiently excited with this technique. The phenomenon is observed in direct space by a Photon Scanning Tunneling Microscope which also allows to test the principle of detection in a subwavelength volume.
Addressing and imaging high optical index dielectric ridges in the optical near field
2001
Experimental observation of light coupling between ${\mathrm{TiO}}_{2}$ integrated waveguides of subwavelength cross section and pure three-dimensional evanescent light fields is reported. This near-field optical phenomenon is produced by controlling the location of the focusing of a laser beam totally reflected at the surface of the sample. The phenomenon is observed in direct space with a photon scanning tunneling microscope. Dielectric ridges several tens of micrometers long have been efficiently excited with this technique. Upon excitation, the extremities of the linear dielectric wires display intense light spots localized both inside and around the ridge. For ridge lengths up to $30\e…
Broadband light trapping in thin film solar cells with self-organized plasmonic nano-colloids
2015
The intense light scattered from metal nanoparticles sustaining surface plasmons makes them attractive for light trapping in photovoltaic applications. However, a strong resonant response from nanoparticle ensembles can only be obtained if the particles have monodisperse physical properties. Presently, the chemical synthesis of colloidal nanoparticles is the method that produces the highest monodispersion in geometry and material quality, with the added benefits of being low-temperature, low-cost, easily scalable and of allowing control of the surface coverage of the deposited particles. In this paper, novel plasmonic back-reflector structures were developed using spherical gold colloids wi…
Pre-determining the location of electromigrated gaps by nonlinear optical imaging
2014
In this paper we describe a nonlinear imaging method employed to spatially map the occurrence of constrictions occurring on an electrically-stressed gold nanowire. The approach consists at measuring the influence of a tightly focused ultrafast pulsed laser on the electronic transport in the nanowire. We found that structural defects distributed along the nanowire are efficient nonlinear optical sources of radiation and that the differential conductance is significantly decreased when the laser is incident on such electrically-induced morphological changes. This imaging technique is applied to pre-determined the location of the electrical failure before it occurs.
Cubic metamaterial crystal supporting broadband isotropic chiral phonons
2021
Chiral metamaterials can support chiral phonons leading to acoustical activity, the acoustical counterpart of optical activity. However, the properties of early metamaterial designs have been very highly anisotropic, and chiral acoustical phonons occurred only for selected high-symmetry directions. The authors propose a novel chiral metamaterial based on ``twisting'' a truncated octahedron in a simple-cubic unit cell. Not supported by crystal symmetry alone but rather by a tuned degeneracy, chiral phonons and large broadband acoustical activity are obtained for all phonon propagation directions in 3D. This result is notable because even isotropic achiral acoustical phonons are rare for crys…
Microcavity Light Emitting Diodes Based on GaN membranes Grown by Molecular Beam Epitaxy on Silicon
2003
Resonant-cavity InGaN/GaN quantum well light emitting diodes have been fabricated. Nitride layers were grown by molecular beam epitaxy on Si (111). We fabricated the structures using a combination of Si substrate etching, GaN etching and dielectric (Ta2O5/SiO2) mirror deposition. The electroluminescence spectra show that the emission within the distributed Bragg reflector stop band is enhanced in the membrane microcavity. The cavity modes are broadened by some cavity length non-uniformity that is introduced when the GaN is back etched to adjust the cavity length. This process does not need any transfer on an intermediate host substrate and is fully compatible with large area semiconductor p…