Temperature dependent polariton emission from strongly coupled organic semiconductor microcavities

We investigated the absorption and photoluminescence (PL) of J-aggregates of a cyanine dye both in a thin film format and when used as the active layer in a strongly-coupled microcavity. We show that as temperature is reduced, the absorption linewidth of the J-aggregates narrows and shifts to higher energy. When the J-aggregate is placed in a microcavity we find that the energy of the polariton modes also shifts to higher energies as temperature is reduced. We compare the intensity of PL emission from the upper and lower branches at resonance as a function of temperature, and find that it can be described by an activation energy of 25 meV. PL emission spectra at resonance also suggest that uncoupled excitons inside the microcavity populate the upper polariton branch states.     

Omnidirectional bandgap in Cantor dielectric multilayers

Analysis of the transmission spectrum of Cantor dielectric multilayers for obliquely incident plane wave shows that the main bandgap shifts towards higher frequencies, substantially retaining its shape, as the incidence angle increases for both s- and p-polarization of the impinging wave. For suitable refractive index values of the two constituent materials a range of frequencies can be found where transmission of the incident wave is almost completely forbidden at any angle of incidence. This omnidirectional bandgap can be found also for lossy media. In this case the stop-band widens as the tangent loss increases, while the depth of the stop-band does not change significantly. Comparison with the periodic quarter-wave stack shows that the Cantor multilayer exhibits a narrower omnidirectional bandgap with transmissivity values that are about one order of magnitude lower.     

Polariton thermalization in GaN microcavities in the strong light–matter coupling regime

We discuss the thermalization of the polariton population from a bulk GaN λ/2 microcavity at room temperature. Simultaneous optical measurements of reflectivity and photoluminescence (PL), as well as time resolved measurements, reveal strong light–matter coupling. Transfer matrix theory is used to calculate reflectivity, absorption, and transmission coefficients for the structure. The PL emission is found to be thermalized, despite its very short lifetime, suggesting the existence of very fast energy relaxation channels.     

Bipolariton laser emission from a GaAs microcavity

Biexciton emission properties were studied in a single GaAs quantum well semiconductor planar microcavity by photoluminescence measurements at low temperatures. At high pump intensity a bipolariton emission appears close to the lower polariton mode. This new mode appears when we detune the cavity resonance out of the lower polariton branch, showing a laser-like behavior. Very small linewidths were measured, lying below 110 μeV and 150 μeV for polariton and bipolariton emission respectively. The input/output power (I/O) measurements show that the bipolariton emission has a weaker coupling efficiency compared to previous results for polariton emission. Varying the pump laser polarization, we were able to show the selection rules for the biexciton particle creation in the quantum well. Simultaneous photoluminescence and near-field measurements show that the polariton and bipolariton emission are spectrally and spatially separated.     

Nano-structural characteristics and optical properties of silver chiral nano-flower sculptured thin films

Silver chiral nano-flowers with 3-, 4- and 5-fold symmetry were produced using oblique angle deposition method in conjunction with the rotation of sample holder with different speeds at different sectors of each revolution corresponding to symmetry order of the acquired nano-flower. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM), were employed to obtain morphology and nano-structure of the films. Optical characteristics of silver chiral nano-flower thin films were obtained using single beam spectrophotometer with both s- and p-polarization incident light at 30° and 70° incidence angles and at different azimuthal angles (φ). Optical spectra showed both TM (TDM (transverse dipole mode) and TQM (transverse quadruple mode)) and LM (longitudinal mode) Plasmon resonance peaks. For 3- and 4-fold symmetry chiral nano-flowers the s-polarization extinction spectra obtained at different azimuthal angles did not show significant change in the Plasmon peak position while 5-fold symmetry chiral nano-flower showed a completely different behavior, which may be the result of increased surface anisotropy, so when the φ angle is changed the s-polarization response from the surface can change more significantly than that for lower symmetries. In general, for 3-, 4- and 5-fold symmetry chiral nano-flowers a sharp peak at lower wavelengths (<450 nm) is observed in the s-polarization spectra, while in addition to this peak a broad peak at longer wavelengths (i.e., LM) observed in the p-polarization spectra, which is more dominant for 70° incidence angle.     

Resonant Effects of FPL and SPP for Light Transmitting through Subwavelength Metallic Gratings

A new model is proposed to explain the physical mechanism of the extraordinary transmission enhancement in subwavelength metallic grating. The extraordinary transmission enhancement is described by the co-operation of Fabry-Perot-like (FPL) resonance and the surface plasmon polariton (SPP) resonance. The rigorous coupled-wave analysis (RCWA) and the finite difference time domain (FDTD) method are employed to illustrate the model by calculating the transmission and the field distributions in the subwavelength metallic grating, respectively. And the numerical calculations show that transmission enhancement is achieved when the coupling resonance of the incident light, the surface plasmon polariton mode and the Fabry-Perot-Like mode is happened, which are in good agreement with the proposed model.     

Surface plasmon wave propagation along single metal wire

Recently,the single metal wire(SW) has become attractive for its potential applications in the terahertz and higher frequency range.However,as the most simple and typical surface plasmon polariton(SPP) transmission line,its study seems far from enough.Many important transmission behaviours have not been explained satisfactorily from the viewpoint of physics.In this paper,making use of the modified Drude model(MDM) based on the Sommerfeld theory,the transmission behaviours of SPPs along SW are systemically investigated theoretically.Some important physical phenomena such as the mode transformation,the lifetime of the radiative mode and the resonance frequency are revealed,and their mechanisms are explored.The results obtained in the paper will facilitate a general understanding of the features and the physical essence of the SPP transmission,not only for SW itself but also for other SPP transmission lines.     

Propagation of a Scattered Electromagnetic Wave with P-Polarization （TE） Mode in Atmospheric Plasma

The finite-difference-time-domain method is applied to simulate the two-dimensional propagation of a p-polarization mode electromagnetic wave in atmospheric plasma and metal layer for strong electron-neutral collisions, It is indicated that for a giving electron density profile, the p-polarization attenuation is very different from the s- polarization attenuation and it depends even strongly on the incident angle. The mechanism of p-polarization attenuation is analysed by the interference of wave and the relationship between the attenuation property and the main parameters is given.     

Excitonic-biexcitonic polariton interference in thin platelet of CuCl

The spectral position in Q-space of the transmission maxima of a 0.15 μm thick CuCl single crystal with parallel plates in Z₃-excitonic resonance region, measured by Mita and Nagasawa, has been interpreted as an indication for the mutual interference effect between two propagating excitonic-biexcitonic polariton modes.     

Coherent effects under suppressed spontaneous emission

An ensemble of resonance atoms is considered, which are doped into a medium with well developed polariton effect, when in the spectrum of polariton states there is a band gap. If an atom with a resonance frequency inside the polariton gap is placed into the medium, the atomic spontaneous emission is suppressed. However, a system of resonance atoms inside the polariton gap can radiate when their coherent interaction is sufficiently strong. Thus the suppression of spontaneous emission for a single atom can be overcome by a collective of atoms radiating coherently. Conditions when such collective effects can appear and their dynamics are analysed. Received 7 June 2000     

Thickness dependence of photoluminescence-decay profiles of exciton-exciton scattering in ZnO thin films

We have investigated the photoluminescence (PL) dynamics of ZnO thin films under intense excitation conditions using an optical-Kerr-gating method. The PL bands originating from exciton-exciton scattering (P emission) and biexciton (M emission) have been observed at 10 K. The ultrashort gating time of 0.6 ps has enabled us to obtain precise information of the temporal profiles of the peak energies and the intensities of the P- and M-PL bands. We have found that the decay time of the P emission becomes longer with increasing film thickness, while that of the M emission is independent of the film thickness. Although the decay time of the P emission is an increasing function of the film thickness, the relation is not in proportion, which is contrary to the predicted proportionality based on a simple model of photon-like polariton propagation.     

Effect of polarization on femtosecond pulsed laser ablation of surface relief gratings using a novel interferometer

In this paper, we report the effects of polarization state of individual beams in ablation of surface relief gratings using a two-beam interferometric technique. We have carried out ablation experiments on (1 1 1) silicon to form surface relief gratings by interfering two femtosecond laser beams under different polarization combinations. Four combinations of polarization were studied, i.e., s-: s-polarization, s-: p-polarization, p-: p-polarization and circular-: circular-polarization (c-: c-polarization). A novel interferometer was used for the investigation. The grating depths, surface roughness and ablation thresholds have been shown to depend on the polarization state of the interfering beams.     

Polaritons in semiconductor/insulator superlattices with nonlocal excitonic response

We report a polariton mode structure calculations based on nonlocal model for semiconductor/insulator superlattices. The reflection spectra and the spatial distributions of intrinsic electric fields near polariton resonance are presented. We show that near the polariton resonance the electric component of polariton mode changes drastically and depends strongly upon the quantum confined exciton wavefunctions.     

Modification of the spontaneous emission of quantum dots near the surface of a three-dimensional colloidal photonic crystal

This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal.In experiments,semiconductor core-shell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated.The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence (PL) measurements.The modification of the spontaneous emission rate,which is reflected in the change of spectral shape and PL lifetime,is clearly observed.While an obvious increase in the PL lifetime is found at most wavelengths in the band gap,a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge.Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal.It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously.This finding provides a simple and effective way for improving the performance of light emitting devices.     

Luminescence of color centers formed in alkali-earth-doped yttrium orthoaluminate crystals

Alkali-earth-doped yttrium orthoaluminate crystals grown in a reducing atmosphere are found to show bright photoluminescence (PL) in visible wavelength regions under the excitation by UV light source. From the results of transmission, PL, PL excitation and time-resolved PL spectra for the samples with different types and concentrations of dopants and the comparison to the results for the samples grown under different conditions, the origin of principal emission is determined to be color centers stabilized by heterovalent ions. The observed fast lifetime and high quantum yield of the luminescence can be explained by dipole-allowed transition between the levels localized in a vacancy. Comparing the effects on the optical properties from several types of dopant ions and taking influence from the UV irradiation into account, a model for the structure of emission centers is proposed.     

Temperature-dependent optical properties of wurtzite InN

Optical properties and carrier recombination dynamics of a series of InN epilayers, with varying free electron concentrations, grown by molecular beam epitaxy were studied by steady-state photoluminescence (PL) and time-resolved differential transmission spectroscopy. At room temperature strong PL around 0.7 eV was observed. Temperature-dependent PL measurements show a redshift of the peak energy and a linear increase of the emission linewidth with temperature. Furthermore, our results demonstrate that room temperature carrier lifetimes are inversely proportional to the free electron concentrations for theses samples. Carrier lifetime as long as 1.3 ns was observed in the best quality sample, indicating a highly improved crystalline quality.     

Total reflection of ultrasound from a ferromagnetic plate with surface pinning of the spins

Using the effective transfer matrix for coupled elastic and spin waves, formulas are derived for the amplitudes of reflection and transmission of right-hand polarized elastic waves incident, in a direction along the normal, on a transversely magnetized ferromagnetic film with homogeneous conditions for pinning of the spins on the surfaces of the film. It is shown that a series of lines with reflectance maxima appears, to the extent of the magnetoelastic coupling, near the magnetoacoustic resonance. The shapes of the spectral line contours and the effect of the thickness of the film and damping are analyzed. The possibility of a similar effect in other polariton systems is discussed.     

Investigation of the relation between photoluminescence intensity and decay time reduction with plasmon effect in InGaAs quantum dots

Plasmonic effects on photoluminescence are investigated via time-integrated and resolved photoluminescence (PL) in epitaxially grown InGaAs quantum dots (QDs). The decay time and PL intensities are compared as a function of the density of Ag nanoplates. Optimal conditions for both reduction lifetime and enhanced PL intensity were found to be a 1:15 ratio of Ag nanoplates to water. Both less and greater than that ratio 1:15, the lifetime increased and the enhancement factor of PL intensity decreased. In addition, the plasmon effect was investigated via resonance wavelength and temperature-dependent PL measurements. At 150K near the resonance conditions between PL from InGaAs QDs and Ag nanoplates, both the lifetime reduction and enhancement factor are maximized. Intensity enhancement is correlated to lifetime reduction for various conditions to identify a condition for maximized enhancement of radiative recombination for designing future ultrafast plasmonic nanolasers.     

Evanescent quadrupole polariton

In this work we demonstrate the formation of a new type of polariton on the interface between a cuprous oxide slab and a polystyrene microsphere placed on the slab. The evanescent field of the resonant whispering gallery mode (WGM) of the microsphere has a substantial gradient, and therefore effectively couples with the quadrupole 1S excitons in cuprous oxide. This evanescent polariton has a long lifetime, which is determined only by its excitonic and WGM component. The polariton lower branch has a well-pronounced minimum. This suggests that this excitation is localized and can be utilized for possible BEC. The spatial coherence of the polariton can be improved by assembling the microspheres into a linear chain.     

Magnetic polariton,impurity mode enhancement,and superradiance effects in FeF2

The first clear evidence for the existence of $\text{magnetic polaritons}$ from a high resolution, far-infrared (FIR) study of the antiferromagnetic resonance (AFMR) of FeF₂ is presented. The broad (4 kOe) asymmetric structure observed in transmission is shown to be a characteristic polariton effect; the linewidth ΔH at 4.2 K is only 350 Oe. The Mn impurity mode is enhanced by ～50 in agreement with a coupled equations of motion prediction. Both host and impurity resonances are broadened by superradiance.