Effect of beam-splitter emission in Fourier-transform emission spectroscopy

A simple model of an emission Fourier-transform spectrometer is provided for a beam splitter with infinitesimal thickness but with general optical properties otherwise. Using the principle of conservation of energy, we derived the rigorous expressions that relate the interferograms from three different signals (source, reference, and beam-splitter emission), which are simultaneously observed by the detector. The relationship among phase and amplitude of the three interferograms is evaluated. The results indicate that the behavior of a Fourier-transform emission spectrometer may be more complicated than what is assumed in some models. Calibration procedures should reflect the implications of this rigorous approach.     

Spontaneous emission in microcavities

The transverse distributions of intensity inside and outside an optical cavity produced by spontaneous emission from atoms inside the cavity are reviewed. The mode properties inside a closed passive one-dimensional cavity are summarised and the spatial distributions of emitted light for a passive cavity with partially transmitting mirrors are discussed. A qualitative theory describes the effects of an amplifying medium inside the cavity, covering the regimes both below and above the lasing threshold. Expressions are derived for the angular spread of the output light in the presence of gain. A theory based on rigorous general relations between gain and noise provides more complete results for the spontaneous emission noise from an amplifying slab within an optical cavity.     

Vibroelectronic emission

A newly discovered effect in which electrons are emitted from a vibrating silver-oxygen-cesium photocathode is described. Pis’ma Zh. Tekh. Fiz. 24, 65–69 (December 12, 1998)     

Greenhouse emission pinch analysis (GEPA) for evaluation of emission reduction strategies

Wastewater treatment plants (WWTPs) are one of the important sources of greenhouse gas (GHG) emission. There is a need for systematical tool that can be used to analyze GHG emission from WWTPs, and to evaluate the associated reduction strategies. In this paper, a systematic analysis methodology, called the greenhouse emission pinch analysis (GEPA), is developed for this purpose. GEPA is graphical in nature, and can be used to analyze the on-site and off-site GHG emissions of the WWTP. Furthermore, three GHG reduction strategies, i.e., increased aeration capacity, external carbon source controller, and reuse of biogas, are evaluated for their environmental load and operational cost reduction using the GEPA. A case study is used to elucidate the proposed method. In this study, the third strategy which reuses biogas from anaerobic digestion shows the largest reduction of GHG emissions.     

Light emission in silicon nanostructures

The many and diverse approaches to materials science problems have greatly enhanced our ability in recent times to engineer the physical properties of semiconductors. Silicon, of all semiconductors, underpins nearly all microelectronics today and will continue to do so for some time to come. However, in optoelectronics and, more recently, in photonics, the severe disadvantage of an indirect band gap has limited the application of elemental silicon. Here we review a number of diverse approaches to engineering efficient light emission in silicon nanostructures. These different approaches are placed in context and their prospects are assessed for applications in silicon-based photonics.     

Resonance RF emission from water

The method and results of an experimental investigation of stable intrinsic RF (microwave) emission from water upon EHF 65 GHz → UHF 1 GHz resonance excitation are described. The Curie point for the radiation quenching is determined at 95°C. The mechanism of emission is explained in terms of conservation of the synchronization and polarization of the superthermal selective oscillations in the molecular system of water, which are induced by a short-term resonance action of linearly polarized EHF radio waves of low intensity.     

Ferroelectric emission studies for electron emission lithography applications

Ferroelectric switching emission, dielectric switching emission, and pyroelectric emission were studied by patterning images on electron resist for electron emission lithography applications. It was observed that the pyroelectric emission is most acceptable for a high throughput 1:1 electron projection lithography application. A 1:1 electron projection lithography was demonstrated by patterning images with line widths of 30 /spl mu/m and using pyroelectric emission. A degradation of the pyroelectric emission property of the material was observed during repeated heating cycles below the phase-transition temperature of the ferroelectric material. Annealing excursions above the phase transition temperature prevented the degradation of the pyroelectric emitter.     

Uncertainties of particle emission probabilities

This paper presents analytical methods for calculating uncertainties of particle emission probabilities, and shows how they are affected by decay-scheme normalization procedures. The equations have been derived with standard mathematical error-propagating techniques, using first-order approximations in Taylor series expansions of emission probabilities.     

Elastic wave emission from damage processes

The theory of elastic wave emission (i.e., acoustic emission; AE) from damage processes such as slip and microcracking is discussed. Analogous developments in the literature on earth-quake seismology and dynamic dislocation theory are noted and utilized. A general representation of the displacement field of an AE event is given in terms of the double-couple response to a distribution of moment density tensor in the source region. Results are specialized to a point source model and to a general far-field analysis of outgoing elastic waves, and conditions for validity of such representations and their low-frequency specializations are noted. Emitted wave fields are compared for tensile opening and slip events, and procedures which might enable the approximate determination of the size or area increase of tensile microcracks are discussed.     

Acoustic emission from subsonic turbulent jets

A method is proposed for determining the noise intensity of subsonic jets. The results are given from a calculation of the far-field intensity level of a jet for various Mach numbers at the nozzle orifice. The results of the calculation are compared with the experimental data.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 4, pp. 711–716, April, 1971.     

Numerical calculations of acoustic emission

Two computer programs which solve the partial differential equations for sound propagation numerically are applied to the study of problems in acoustic emission. The programs use finite difference and finite element techniques to calculate sound fields due to distributions of sources in complex geometries in two dimensions. The potential to handle more complex geometries and to model more realistic sources is the main advantage of these numerical calculations over the analytic calculations. The main disadvantage of the numerical techniques is the cost of obtaining results since a large main frame computer or supercomputer is required. Both numerical methods are found to agree well with analytic calculations using Green's functions. The finite difference method agrees very well with the analytic calculations but, in its current implementation, is much slower and contains more numerical noise compared to the finite element method. The finite element method has the additional advantage of being capable of handling more complex geometries than the finite difference method.     

Field emission in doped nanotubes

Doping into nanotubes is an attractive and significant way to tailor their electron transport and emission properties. This article reviews some recent experimental and theoretical advances in the studies of doping behaviors in carbon nanotubes and gallium nitrogen nanotubes, and doping effects on their field electron emission properties. The general theory for field emission mechanism of one-dimensional nanosystems is presented to provide an overall picture of the field emission process and doping behavior. Potential applications of doped nanotubes as diverse nanoscale emitters, microscopy probes, electronic guns and nanoelectronic devices are discussed.     

Planar array infrared emission spectroscopy

Planar array infrared spectroscopy (PA-IR) is shown to be a powerful new approach to infrared emission spectroscopy (IRES). A proof-of-concept study of selected polymers indicates that PA-IRES allows acquisition of emission spectra with a high signal-to-noise ratio at temperatures as low as 80 degrees C. It is shown that a time resolution below 20 ms is readily achievable for time-resolved characterization of single non-repeatable events. The possibility of recording spatially resolved emission spectra is also demonstrated, and potential applications of this novel technique are finally described.     

Acoustic emission sources modelled by dislocations

Acoustic emission sources representing dislocations and cracks under tensile forces, shear forces or a combination of these forces are modelled by a single circular dislocation loop and by a continuous distribution of such loops. The medium is assumed to be linear, elastic isotropic, homogeneous and unbounded. The quasistatic and the point source approximations are assumed. The wave displacement induced by the expansion of a loop and of a continuous distribution of loops is calculated for a tensile and a shear source on the basis of the dynamic dislocation theory by using the Green's function formalism. The wave is given in terms of L-, SV- and SH-waves as a function of the expansion law of the source and is calculated in a simple case. The wave form, radiation pattern and the diameter of the source are calculated; the influence of the expansion time of the source and of the distance between the source and the observation point is discussed. The results are used to check the assumptions of linearity and elasticity. They are compared with experiments and applied to characterise the source from measurements.     

Improved acoustic emission locations

Acoustic emission locations have been determined in a modest-size specimen of Westerly granite ( 50×50×200 mm) under uniaxial compressive loading to failure. Periodically during the experiment acoustic pulses were transmitted from a set of source transducers to an acoustic emission receiver array. Axial and transverse velocities were determined from these transmission data. The piezoelectric transducers used in this study were too large to be treated as points. A separate experiment was performed to determine the effect of finite transducer size and incident angle on observed arrival times. Velocity pulse arrival times were inverted for the known source transducer positions using (1) an isotropic, fixed velocity model, (2) the observed anisotropic, stress dependent velocity field, and (3) transducer size corrections. Incorporation of the observed velocity field and transducer size effects dramatically improved location accuracy. Acoustic emissions were located using this technique. Synthetic data, exact and with realistic errors, were inverted to determine location uncertainties at various locations throughout the sample. Suggestions are made for further improvements.     

Field emission deposition sources

A new metal ion deposition process, field emission deposition, is described in which ions, clusters and droplets are extracted directly from the melt by an electric field. Films deposited in this way exhibit interesting physical, metallurgical and electrical properties.     

Surface-enhanced emission from single semiconductor nanoribbons

Emission enhancement from single semiconductor CdSe nanoribbons by introduction of surface plasmon polaritons (SPPs) via Au contacts is studied. Scanning confocal microscopy is employed to investigate the emission enhancement behavior via photoluminescence measurements. Large enhancement factors of 77-130 at a peak emission of CdSe of ～710 nm are obtained, which are ascribed to the gain-assisted propagation of the short-range mode of SPPs. Our findings open the exciting possibilities for high-efficiency SPP-enhanced light-emitting devices based on luminous bodies with finite lateral dimensions.     

Optical emission of InAs nanowires

Wurtzite InAs nanowire samples grown by chemical beam epitaxy have been analyzed by photoluminescence spectroscopy. The nanowires exhibit two main optical emission bands at low temperatures. They are attributed to the recombination of carriers in quantum well structures, formed by zincblende-wurtzite alternating layers, and to the donor-acceptor pair. The blue-shift observed in the former emission band when the excitation power is increased is in good agreement with the type-II band alignment between the wurtzite and zincblende sections predicted by previous theoretical works. When increasing the temperature and the excitation power successively, an additional band attributed to the band-to-band recombination from wurtzite InAs appears. We estimated a lower bound for the wurtzite band gap energy of approximately 0.46?eV at low temperature.     

Cesium microwave emission without population inversion

The use of coherent population trapping (CPT) for the realization of a Cs coherent microwave emitter without population inversion is described. Preliminary experimental results are reported regarding the radio frequency spectrum of the emitted microwave radiation, the emission profile width, and the transient behavior of the output power. This new approach, based on the coherence properties of the laser radiation, allows the implementation of a microwave frequency standard where the linear light shift is absent and the thermal noise limit for the frequency instability is below 10(-12) for an integration time of 1 s.     

Quantum interference in double photon emission

We study Fano-like interference in double photon absorption, describing quantum beats in the second-order correlation function for both a free Λ-V system and a driven four-level scheme which approximately reproduces the first one in the dressed state picture. Because of interference, both amplitude and frequency of the beat oscillations are modified and (in some case) suppressed. In the case of the driven system, a partial coherent control of these features can be obtained, even in the presence of spontaneous emission for the driven transition.