24 research outputs found
Plasmonic-enhanced photoluminescence in porous silicon with pore-embedded gold nanoparticles fabricated by direct reduction of chloroauric acid
The low efficiency of porous silicon (p-Si) luminescence hinders the
development of silicon-based optoelectronic devices. The increase in p-Si
emission using near-field enhancement, owing to the incorporation of gold
nanoparticles (AuNPs) into the photonic structure, is probably the most viable
alternative. However, the coupling of plasmon resonance to p-Si emission is
challenging because of the difficulty in controlling the size and location of
the AuNPs with respect to the emissive p-Si layer. In this study, AuNPs were
synthesized by clean direct reduction of chloroauric acid inside a p-Si
photonic structure. As a result, AuNPs could be synthesized all along the pores
of the p-Si structure, allowing to obtain a six-fold enhancement of the p-Si
photoluminescence, specifically for the emission band at 567 nm owing to the
plasmon effect. Possible applications of this hybrid material include
light-emitting devices and photoluminescence-based sensors
Room-temperature polariton repulsion and ultra-strong coupling for a non-trivial topological one-dimensional tunable Fibonacci-conjugated porous-Silicon photonic quasi-crystal showing quasi bound-states-in-the-continuum
Room temperature strong coupling from CdSeS/Zn quantum-dots embedded into a
tunable porous-silicon Fibonacci-conjugated array could be observed when
exciton's energy was tuned either to the photonic-edge or the defect in the
middle of the pseudo-bandgap region of the 1D cavity. Both, the photonic-edge
and the defect could be identified as topological edge modes and
quasi-bound-states-in-the-continuum, where large density of states and field
localization over a wider bandwidth produce a broadband Purcell enhancement,
helping to optimize the coupling among the exciton and the 1D photonic
quasi-crystal despite the natural difficulty to make the quantum dots to
penetrate the cavity pores. A clear repulsion among polaritons, amounting to
almost 8 meV for in-plane k values when the cavity energy is larger than the
exciton one (blue k-detuning), was measured when increasing the incident light
fluence, marking the potential of this non-trivial topological array for
achieving polariton quantum blockade. Evidence for ultra-strong coupling, where
a shift as large as 20 meV, could be found when the defect of the
pseudo-bandgap region of the cavity was tuned to the exciton
Ablation and optical third-order nonlinearities in Ag nanoparticles
The optical damage associated with high intensity laser excitation of silver nanoparticles (NPs) was studied. In order to investigate the mechanisms of optical nonlinearity of a nanocomposite and their relation with its ablation threshold, a high-purity silica sample implanted with Ag ions was exposed to different nanosecond and picosecond laser irradiations. The magnitude and sign of picosecond refractive and absorptive nonlinearities were measured near and far from the surface plasmon resonance (SPR) of the Ag NPs with a self-diffraction technique. Saturable optical absorption and electronic polarization related to self-focusing were identified. Linear absorption is the main process involved in nanosecond laser ablation, but non-linearities are important for ultrashort picosecond pulses when the absorptive process become significantly dependent on the irradiance. We estimated that near the resonance, picosecond intraband transitions allow an expanded distribution of energy among the NPs, in comparison to the energy distribution resulting in a case of far from resonance, when the most important absorption takes place in silica. We measured important differences in the ablation threshold and we estimated that the high selectiveness of the SPR of Ag NPs as well as their corresponding optical nonlinearities can be strongly significant for laser-induced controlled explosions, with potential applications for biomedical photothermal processes
Anisotropic Second- and Third-Order Nonlinear Optical Response from Anisotropy-Controlled Metallic Nanocomposites
Effect of size and composition on the second harmonic generation from lithium niobate powders at different excitation wavelengths
INVESTIGACIÓN DESARROLLADA EN COLABORACIÓN DE RED TEMATICA PRODEP /SEP/MEXICOLiNbO3 microcrystalline systems, possessing almost stoichiometric composition, were produced by varying the temperature and time parameters in the annealing processes following a mechanochemical reaction of raw powders. SHG from these samples, detected for every fundamental wavelength in the range 800-1300 nm, and being maximal at a certain wavelength, λmax, for each sample, has been addressed to a random scattering of the induced nonlinear polarizations. Possible tuning of λmax could be ascribed to control of composition and grain size of the sample. Random orientation of the produced nanocrystallites was verified since no dependence for SHG intensity on incident polarization was observed.PAPIIT-UNAM through grant IN117116 Y “RED PRODEP-SEP Compuestos poliméricos propiedades y aplicaciones 2015-2016
Room-Temperature CsPbBr Mixed Polaritons States
Light-matter interactions are known to lead to the formation of polariton
states through what is called strong coupling, leading to the formation of two
hybrid states usually tagged as Upper and Lower Polaritons. Here, we consider a
similar interaction between excitons and photons in the realm of strong
interactions, with the difference that it enables us to obtain a
mixed-polariton state. In this case, the energy of this mixed state is found
between the energies of the exciton state and the cavity mode, resulting in an
imaginary coupling coefficient related to a specific class of singular points.
These mixed states are often considered unobservable, although they are
predicted well when the dressed states of a two-level atom are considered.
However, intense light confinement can be obtained by using a Bound State in
the Continuum, reducing the damping rates, and enabling the observation of
mixed states resulting from the correct kind of exceptional point giving place
to strong coupling. In this study, using the Transfer Matrix Method, we
simulated cavities made of porous silicon coupled with CsPbBr3 perovskite
quantum dots to numerically observe the mixed states as well as experimentally,
by fabricating appropriate samples. The dispersion relation of the mixed states
is fitted using the same equation as that used for strong coupling but
considering a complex coupling coefficient, which is directly related to the
appropriate type of exceptional point
Stark effect in a wedge-shaped quantum box
The effect of an external applied electric field on the electronic ground
state energy of a quantum box with a geometry defined by a wedge is studied by
carrying out a variational calculation. This geometry could be used as an
approximation for a tip of a cantilever of an atomic force microscope. We study
theoretically the Stark effect as function of the parameters of the wedge: its
diameter, angular aperture and thickness; as well as function of the intensity
of the external electric field applied along the axis of the wedge in both
directions; pushing the carrier towards the wider or the narrower parts. A
confining electronic effect, which is sharper as the wedge dimensions are
smaller, is clearly observed for the first case. Besides, the sign of the Stark
shift changes when the angular aperture is changed from small angles to angles
theta>pi. For the opposite field, the electronic confinement for large
diameters is very small and it is also observed that the Stark shift is almost
independent with respect to the angular aperture.Comment: 23 pages, 9 figures, 1 tabl
Optical 3D-storage in sol-gel materials with a reading by Optical Coherence Tomography-technique
We report on the recording of 3D optical memories in sol-gel materials by
using a non-linear absorption effect. This effect induces a local change of the
optical properties of the material which is read and quantified with a high
resolution full-field Optical Coherence Tomography setup. It is the first time
that this technique is used for this purpose. Data recording was performed by
focused picosecond (ps) single-pulse irradiation at 1064 nm with energy
densities of 10 and 33 J/cm2 per pulse.Comment: 19 pages, 7 figure