M. E. Sasin

Tamm plasmon polaritons: Slow and spatially compact light

We report on the first experimental observation of Tamm plasmon polaritons (TPPs) formed at the interface between a metal and a dielectric Bragg reflector (DBR). In contrast to conventional surface plasmons, TPPs have an in-plane wavevector less than the wavevector of light in vacuum, which allows for their direct optical excitation. The angular resolved reflectivity and transmission spectra of a GaAs∕AlAs DBR covered by Au films of various thicknesses show the resonances associated with the TPP at low temperatures and room temperature. The in-plane dispersion of TTPs is parabolic with an effective mass of 4×10−5 of the free electron mass.

Experimental Demonstration of Reduced Light Absorption by Intracavity Metallic Layers in Tamm Plasmon-based Microcavity

We demonstrate experimentally a microcavity based on SiO2/TiO2 with two gold layers directly attached to the central base of the microcavity. The design of optical modes based on the peculiarities of Tamm plasmons provides reduced absorption due to the fixing of the node of the electric field of optical mode to metallic layers. Experimentally measured reflection and transmission spectra exhibits three features, corresponding to three hybrid modes of the microcavity. The widths of spectral features confirm that absorption of light by metallic layers is vanishing for optimized mode. The latter is confirmed by resonant transmission of light through the structure. In case of the laser structure, two intracavity metallic layers could serve as contacts for electrical pumping.

The effect of a UV preionization pulse on short-wave radiation output from a laser-produced-plasma source with a Xe gas-jet target

Experiments aimed to raise the emissivity of a laser-produced plasma source with a Xe gas target in the far-UV spectral range are described. In these experiments, the main pulse of the IR Nd:YAG laser was preceded by a pre-ionization pulse of a UV KrF excimer laser. The consequences of applying the prepulse and its influence on the short-wavelength emission intensity were traced up to main-pulse delays of about 5 μs with respect to the prepulse. It is supposed that the main mechanism by which the prepulse affects the evolution of the plasma and its emission intensity is related to the density waves excited in the gas target by this pulse.

Ionization dynamics in the laser plasma in a low pressure gas target

In Xe-laser-plasma short-wave-radiation sources, the laser-energy-to-EUV conversion efficiency (CE) turns out to be substantially lower than theoretical expectations. An estimation made in the present work is evidence of what a long period of the primary ionization, lasting up to a moment when high-Z ions appear to emit short-wave photons, can be considered as a main cause for the low CE values. During that period the plasma remains low-ionized and absorbs weakly the laser energy. Data deduced from laser light absorption measurements confirm the estimation above. A preionization of the gas target with the UV excimer laser pulse is proposed as a method to accelerate the ionization process.

The effect of a “Coulomb well” on the absorption and magnetoabsorption spectra of strained InGaAs/GaAs heterostructures

The optical and magnetooptical properties of strained InGaAs/GaAs quantum-well heterostructures grown by molecular-beam epitaxy were studied at T=1.7 K in magnetic fields B⩽7.5 T. The well-resolved oscillatory structure of the magnetoabsorption spectra makes it possible to reproduce the “fan diagrams” for transitions between Landau levels of the HH1E1 quantum-confined states, taking into account exciton binding energies calculated variationally. Based on these results, reduced cyclotron masses of carriers were calculated for quantum wells with various indium contents. A self-consistent variational solution to the exciton problem in the structure under study shows that for weak type-II potentials the effect of Coulomb localization of the hole leads to a relative increase in the oscillator strength of the LH1E1 exciton transition. In this case the LH1E1 and LH3E1 exciton transitions remain spatially direct and retain a considerable intensity. The calculated splitting of ∼9 meV between these two states in zero magnetic field is found to be in agreement with experiment. The significant oscillator strength of light-hole excitons, along with the observed doublet structure, are experimental confirmations that electron-hole attraction can transform a rather low barrier for light holes in a type-II structure into a quantum well with a parabolic “Coulomb” shape near its bottom, i.e., a “Coulomb well.”

Computational simulation of laser plasma emission with shock-wave-affected density distribution in the gas-jet target

Based on the results of numerical fluid dynamics simulation, an imitation parameter has been constructed which simulates the observed intensity of the laser plasma emission in a short-wave range. Within the computational model frame, a high-temperature perturbation is created in the jet that generates a strong shock wave. The resultant complicated target structure and its evolution lead to nonmonotonic time variations of the simulation parameter. This result agrees well with the experimentally measured behavior of emission from the laser plasma formed on the target perturbed by an additional laser prepulse.

Cylindrical multilayer metal–dielectric structures

A method of creating a cylindrical structures consisting of thin metallic layer and dielectric multilayer Bragg reflector is described. Formation of the structures is observed experimentally as a result of separation and twisting away from the substrate a thin layer of gold coated with a multilayer SiO2/TiO2 Bragg reflector. It is suggested that such structures may be of interest for the creation of novel optoelectronic devices.

Features of experimental spectra of the laser plasma with a dense xenon gas-jet target in the extreme ultraviolet range

Emission spectra in the wavelength range of 5–25 nm of the laser plasma produced using a gas jet of Xe and a mixture of Xe + Ar with an atomic density of up to 7 × 1018 cm–3 are described. There are no discrete spectral lines in the xenon spectra, but a wide continuous peak of the radiation is observed within the 9–14 nm wavelength band. At variations of experimental conditions, its maximum demonstrates a regular wavelength shift, which is attributed to the corresponding change in the plasma temperature. Another feature is an only slight decrease in the intensity of xenon emission when the target is strongly diluted with argon.

Above-barrier excitons: First magnetooptic investigation

An above-barrier localized excitonic state in a Bragg confining semiconductor superstructure based on an (In, Ga)As/GaAs heterosystem is observed experimentally. A sharp excitonic resonance corresponding to the interference mechanism of localization is observed in the absorption spectrum of this structure at 1.548 eV, i.e., 33 meV above the energy of a bulk exciton in GaAs. The oscillator strength of the above-barrier exciton is twice that of the main excitonic state in the system, and the above-barrier exciton gives rise to sharp Landau oscillations in the magnetoabsorption spectra.

Absorption of the laser radiation by the laser plasma with gas microjet targets

An upper limit of absorption of the laser radiation in the plasma produced in a gas jet Xe target with the average density of (3–6) × 1018 cm–3 and the effective diameter of 0.7 mm is found. It is equal to ≈50% and remains constant under any variation in this range of densities. This result contradicts both theoretical assessments that have predicted virtually complete absorption and results of earlier experiments with the laser spark in an unlimited stationary Xe gas with the same density, where the upper limit of absorption was close to 100%. An analysis shows that nonlinearity of absorption and plasma nonequilibrium lead to the reduction of the absorption coefficient that, along with the limited size of plasma, can explain the experimental results.