Low pressure gain measurements in KrF

Optical gain at 248 nm is measured in low pressure krypton/fluorine mixtures excited by an electron-beam. Measurable gain is observed down to a pressure of 50 mbar. Results are compared with the predictions of a simple kinetic model. The application of low pressure operation to ultra high power short pulse amplifiers is discussed.     

Line scattering images on admixtures in alkali-halides

Different types of line scattering images in cubic crystals are discussed and a method for finding the distribution of rods in the basic substance by means of the scattering image is demonstrated on NaCl:SrCl₂. It is shown that the rods in NaCl:SrCl₂ are distributed in all equivalent 141 directions with the same probability.     

光在随机增益介质中的放大

 结合环形腔理论,运用蒙特卡罗法模拟了光子在介质中的随机行走。研究了倍频Nd:YAG（脉宽6 ns,频率20 Hz）脉冲激光器作为泵浦光,在TiO₂ / 若丹明 B有机增益介质中,散射微粒的颗粒密度和泵浦光面积对随机激光器阈值强度的影响。模拟结果表明：随机激光阈值和光子在增益介质中的随机行走路程长度和光子通过边界返回增益区和非增益区的几率有关。随着泵浦光面积的增加,随机激光器阈值降低;增益介质中散射颗粒密度的增加降低了随机激光器的阈值。     

光在随机增益介质中的放大

结合环形腔理论,运用蒙特卡罗法模拟了光子在介质中的随机行走。研究了倍频Nd:YAG（脉宽6 ns,频率20 Hz）脉冲激光器作为泵浦光,在TiO2 / 若丹明 B有机增益介质中,散射微粒的颗粒密度和泵浦光面积对随机激光器阈值强度的影响。模拟结果表明：随机激光阈值和光子在增益介质中的随机行走路程长度和光子通过边界返回增益区和非增益区的几率有关。随着泵浦光面积的增加,随机激光器阈值降低;增益介质中散射颗粒密度的增加降低了随机激光器的阈值。     

Optical properties of doped quasi-two-dimensional systems

A wide class of experimental data on luminescence in doped two-dimensional systems is explained in terms of multiphonon optical transitions. A zero-radius-potential model is employed to describe localized states in square quantum wells. Specifically, it is shown that the luminescence intensity varies nonmonotonically with the acceptor-impurity position, whereas the half-width of the luminescence peak decreases with the impurity distance from the center of the size-confined system. The features of luminescence in a longitudinal magnetic field are investigated.     

Optical gain in GaSe due to exciton-exciton recombination

Measurements of the optical gain spectrum in high quality GaSe are reported. The mechanism for light amplification has been investigated, giving evidence that the exciton-exciton scattering process is responsible for stimulated emission.     

PbTe/CdTe量子点的光学增益

PbTe/CdTe量子点是一类新型异系低维结构材料,实验发现具有强的室温中红外光致发光现象.为研究这一材料体系的发光特性,建立了理论模型,计算了PbTe/CdTe量子点的光学跃迁和增益.模型基于k·p包络波函数方法并考虑了PbTe能带结构的各向异性.分析了量子点光学增益与量子点尺寸、注入载流子浓度的关系.结果表明,当注入载流子浓度在(0.3—3)×10¹⁸cm^-3范围时,尺寸为15—20nm的量子点可以产生 关键词： PbTe/CdTe量子点 光学增益 铅盐矿半导体     

Negative probabilities and information gain in weak measurements

We study the outcomes in a general measurement with postselection, and derive upper bounds for the pointer readings in weak measurement. The probabilities inferred from weak measurements change along with the coupling strength; and the true probabilities can be obtained when the coupling is strong enough. By calculating the information gain of the measuring device about which path the particles pass through, we show that the “negative probabilities” only emerge for cases when the information gain is little due to very weak coupling between the measuring device and the particles. When the coupling strength increases, we can unambiguously determine whether a particle passes through a given path every time, hence the average shifts always represent true probabilities, and the strange “negatives probabilities” disappear.     

Optical properties of doped graphene layers

The reflectance of a graphene monolayer, as well as of a system of monolayers, is calculated in the infrared range. A quantum expression for the conductivity in the collisionless regime that depends on the frequency, the temperature, and the concentration of carriers is used in the calculations. Above the threshold of the interband electron absorption, the reflectance decreases with increasing frequency. With decreasing temperature, excitation of plasmons in the system of layers is possible in a narrow range near the threshold, which results in the occurrence of a deep and sharp minimum in the frequency dependence of the reflectance.     

Conductivity and Hall effect measurements in doped polyacetylene

Conductivity and Hall effect measurements are reported for polyacetylene films heavily doped with AsF₅. The Hall coefficient is anomalously small, however, it is p-type and relatively temperature insensitive in the range 4–300 K indicative of metallic conduction. The effects of film degration by heating and air exposure are also investigated.     

Optical storage in doped microstructures of alkali halides

Peculiarities of colour centres production and their recombination in photostimulated processes in doped alkali halide microstructures were examined in connection with their practical use as active photostimulable media in miniaturised optoelectronic and photonic devices. The specific interaction of unrelaxed H-centres and electrons with the dopants in different valence and electronic states open a way for widening the scope of multifunctional (logical and mathematical) optical data processing and transfer.     

Optical bistability in Coumarin-450 doped polymeric samples

Experimental observations of optical bistability in Coumarin-450 dye molecule entrapped in polymeric (PMMA) host inside Fabry–Perot cavity have been reported. Efforts have been made to demonstrate the nonlinear behavior of optical materials in solid form using 532 nm of Nd: YAG laser. The nonlinearity in terms of optical bistability and excited state absorption (ESA) has been discussed. The nonlinearity in Coumarin-450 dye molecule originated from unique intensity dependence of the complex index of refraction. It has been observed that nonlinear refraction dominates over nonlinear absorption in giving rise to the optical bistability. Nonlinear refractive index in both polymeric and liquid samples has been calculated.     

Absorption spectra of excitons in alkali-halides in the vacuum-ultra-violet region

On the basis of the localized excitation model, the spectra of K⁺ - 3p electron excitation in potassium halides are studied theoretically by using methods of the ligand field theory and a good agreement with the experiment is obtained. Some discussions are given on the applicability of the Frenkel exciton model to the VUV spectra of other alkali halides.     

Optical and thermal properties of doped semiconductor

The knowledge of doping effects on optical and thermal properties of semiconductors is crucial for the development of optoelectronic compounds. The purpose of this work is to investigate theses effects by mirage effect technique and spectroscopic ellipsometry SE. The absorption spectra measured for differently doped Si and GaAs bulk samples, show that absorption in the near IR increases with dopant density and also the band gap shifts toward low energies. This behavior is due to free carrier absorption which could be obtained by subtracting phonon assisted absorption from the measured spectrum. This carrier absorption is related to the dopant density throw a semi-empirical model.     

Optical properties of laser-induced heavily doped Si

An analysis of recently reported experimental studies⁽¹⁾ of the optical properties of laser-induced heavily doped Si layers is presented here. The analysis has been made on the basis of models like those of Penn⁽²⁾ and Breckenridge et al.⁽³⁾ Our calculations show that, in general, N_eff, the effective number of electrons contributing to optically induced electronic transitions, increases as does ε₂(E), the imaginary part of the complex dielectric constant. This reflects an increased absorption coefficient for these As-doped samples. These studies have been carried out on samples of Si heavily doped by ion-implantation followed by a laser-annealing process. The conclusions based on these studies are seen to be in accord with those of Aspnes et al.⁽⁴⁾ and Vina and Cardona.⁽⁵⁾     

Hall effect measurements on transmutation doped semiconductors

Transmutation doping of semiconductors by neutron irradiation is a well known technique, mainly applied to achieve an extremely uniform low level n-doping of large Si crystals via the ³⁰Si(n,γ)³¹Si→³¹P nuclear reaction. Similar experiments in other semiconductors never gained a comparable importance. In the last years, however, it has been shown that the doping of semiconductors by implanting radioactive isotopes can yield valuable information about the processes occurring during the incorporation of dopant atoms into the lattice as well as the defect–dopant interactions occurring after the decay of the unstable isotope to a daughter isotope with usually different elemental properties. In this contribution, Hall effect measurements carried out so far on implanted radioactive dopants will be reviewed. The specific problems and the potential of the method will be discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optical properties of samarium doped zinc-phosphate glasses

Samarium doped zinc-phosphate glasses having composition Sm₂O_{3 (x)}ZnO_(60−x) P₂O_{5 (40)} (where x=0.1-0.5 mol%) were prepared by melt quenching method. The density of these glasses was measured by Archimedes method; the corresponding molar volumes have also been calculated. The values of density range from 3.34 to 3.87 gm/cm³ and those of molar volume range from 27.62 to 31.80 cm⁻³. The optical absorbance studies were carried out on these glasses to measure their energy band gaps. The absorption spectra of these glasses were recorded in UV-visible region. No sharp edges were found in the optical spectra, which verifies the amorphous nature of these glasses. The optical band gap energies for these glasses were found to be in the range of 2.89-4.20 eV. The refractive index and polarizability of oxide ion have been calculated by using Lorentz-Lorentz relations. The values of refractive index range from 2.13 to 2.42 and those of polarizability of oxide ion range from 6.51×10⁻²⁴ to 7.80×10⁻²⁴ cm³.     

Optical absorption studies on cobalt doped struvite

Abstract

Optical absorption spectrum of cobalt doped MgNH₄PO₄ · 6H₂O (struvite) is investigated in UV-VIS-NIR regions. The spectrum in UV-VIS-NIR region is attributed to Co²⁺ in octahedral symmetry whereas the IR spectrum is attributed to vibrations due to PO₄ ^3-, NH₄ ⁺ and H₂O. The following crystal field (Dq) and interelectronic repulsion (B, C) parameters are evaluated: Dq = 940cm^?1, B = 870cm^?1 and C = 3970cm^?1.     

Optical bistability in defective photonic multilayers doped by graphene

We study the optical bistability (OB) in photonic multilayers doped by graphene sheets, stacking two Bragg reflectors with a defect layer between the reflectors. OB stems from the nonlinear effect of graphene, so the local field of defect mode (DM) could enhance the nonlinearity and reduce the thresholds of bistability. The structure achieves the tunability of bistability due to that the DM frequency and transmittance could be modulated by the chemical potential. Bistability thresholds and interval of the two stable states could be remarkably reduced by decreasing the chemical potential. A lager Bragg periodic number could increase the localizing of field, but the graphene loss may decrease the intensity of transmission light. We have concluded an appropriate periodic number to achieve OB. The study suggests that the tunable bistability of the structure could be used for all-optical switches in optical communication systems.