Angular Distribution Of Emission Research Articles

VCSEL end-pumped passively Q-switched Nd:YAG laser with adjustable pulse energy

A compact, passively Q-switched Nd:YAG laser utilizing a Cr4+:YAG saturable absorber, is end-pumped by the focused emission from an 804 nm vertical-cavity surface-emitting laser (VCSEL) array. By changing the VCSEL operating current, we demonstrated 2x adjustability in the laser output pulse energy, from 9 mJ to 18 mJ. This energy variation was attributed to changes in the angular distribution of VCSEL emission with drive current, resulting in a change in the pump intensity distribution generated by a pump-light-focusing lens.

Angular Distribution of Argon Ions and X-Ray Emissions in the Apf Plasma Focus Device

Angular distribution of ion beam emission from an argon gas-filled plasma focus devices has been investigated using an array of five Faraday cups. The argon ion beam emission is found to be highly pressure-dependent and reaches its maximum at the pressure of 1 torr. The ions flux decreased as the working pressure increased; the maximum ion density at 1 torr was estimated to be around 9.24 × 1024 ions/steradian. Also, the study on the angular distribution of X-rays has been carried out using TLD-100 dosimeters. The intensity of ions reduced significantly at angles higher than ±11° but the X-ray distribution was bimodal, peaked approximately at ±15°.

Experimental Study on the Importance of Accurate Neutron Angular Distribution Measurement for Determination of Neutron Yield in a 2.5 kJ Mather type PF

Three activation counters were constructed by thin wall Geiger and were placed in different angels with respect to anode axis; 0°, 45°, 90°; where the Geigers have 20 cm distance from anode top of the 2.5 kJ SBUPF1 plasma focus device. The counters were calibrated by a 5 Ci Am–Be neutron source with source removal method. A computer program receives the Results of each plasma focus experiment and background count rates, estimates the angular distribution of neutron emission and calculates the neutron yield of each shot. The neutron yield of the device was measured about 6 × 107 neutrons per shot. The results, indicate that using three counters (instead of one counter in 0°) in different angles for determination of total neutron yield, gives a more accurate measurement (up to 28% is measured in sample shots), and this error is bigger in those shots that thermonuclear fusion mechanism have greater share in neutron production.

Angular distribution of liquid droplets during the laser ablation of silicon target

AbstractPulsed laser deposition of thin films involves an extremely complex process, and therefore, the study of the different aspects of the basic mechanism of laser ablation is still under investigation and development.In this work, the initial stages of laser ablation process have been studied by considering the roughness of the deposited surfaces, their continuous morphological changes and the angular distribution of liquid droplets produced by laser irradiation.Various experiments on silicon wafers, using a KrF excimer laser (248 nm) impinging at 45° with respect to the target were performed. Scanning electron microscopy technique was used to investigate the morphological changes of the silicon surface and the angular emission distribution of the liquid droplets. Copyright © 2010 John Wiley & Sons, Ltd.

Nuclear data evaluation methodology including estimates of covariances

Evaluated nuclear data rather than raw experimental and theoretical information are employed in nuclear applications such as the design of nuclear energy systems. Therefore, the process by which such information is produced and ultimately used is of critical interest to the nuclear science community. This paper provides an overview of various contemporary methods employed to generate evaluated cross sections and related physical quantities such as particle emission angular distributions and energy spectra. The emphasis here is on data associated with neutron induced reaction processes, with consideration of the uncertainties in these data, and on the more recent evaluation methods, e.g., those that are based on stochastic (Monte Carlo) techniques. There is no unique way to perform such evaluations, nor are nuclear data evaluators united in their opinions as to which methods are superior to the others in various circumstances. In some cases it is not critical which approaches are used as long as there is consistency and proper use is made of the available physical information. However, in other instances there are definite advantages to using particular methods as opposed to other options. Some of these distinctions are discussed in this paper and suggestions are offered regarding fruitful areas for future research in the development of evaluation methodology.

Bremsstrahlung emission accompanying α-decay of deformed nuclei

A fully quantum model describing the angular distribution of the bremsstrahlung photon emission accompanying the α-decay of a deformed nucleus is presented for the first time. An analytical dependence of the bremsstrahlung probability on the quadrupole deformation parameter β 2 of the decaying nucleus has been found. Such a model and the detailed formalism allow us to calculate the stable spectra of the bremsstrahlung emission probability for different values of the angle between the direction of the α-particle motion and the symmetry axis of the decaying nucleus. We present the results of this new model by the calculation of the photon emission probability accompanying the α-decay of the 226Ra nucleus which has the nuclear deformation parameter β 2 = 0.151 . The results show by a clear way the role and the influence of the nuclear deformation of the decaying nucleus on the bremsstrahlung photon spectrum.

Polarization-gated surface enhanced optical fields for ultrafast electron acceleration

We show that the field polarization of the surface-plasmon-resonance enhanced optical field can be controlled to be linear with doubled intensity enhancement by using the polarization-gated excitation scheme with two counter-incident femtosecond laser pulses under the Kretschmann configuration, which is hence used for ultrafast electron acceleration to increase the maximum kinetic energy. The spatiotemporal evolution of the polarization-gated surface-enhanced optical field is studied by means of a simplified analytical model to describe the dynamical processes of electron acceleration, the kinetic energy and emission angular distributions of the accelerated electrons.

Excited state distribution of reflected hydrogen atoms at metal surfaces – Development of theoretical models

Numerical methods were developed to study single electron capture by translating hydrogen atoms above metal surfaces. The present method gives predictions for hitherto unknown population distribution of excited species in hydrogen atoms reflected at the metal surfaces. The excited state abundance was calculated for Mo surface. Kinetic energy distribution of the reflected atoms was taken into account with the aid of the Monte-Carlo simulation code (ACAT). Energy distribution associated with the 3d 2 excited state in reflected neutrals consistently explains peak energy variation with incident energies of Doppler-shifted D α lines measured by Tanabe et al. Occupation probability of the magnetic sub-levels is obtained to be highly polarized. It suggests strong anisotropy in angular distribution of photon emission from the excited states created via the surface electron capture.

Electromagnetic Radiation from Organic Light-emitting Diodes

An analytical prototype model for the electromagnetic radiation emitted from a nanometric organic light-emitting diode device is presented and thoroughly investigated herein. The results are obtained via asymptotic evaluation of the resultant radiation integral in con- junction with coherence considerations, resulting in closed-form analytical expressions. For the sake of simplicity and clarity, we focus on a two-dimensional canonical conflguration excited by impulsive (line) sources. The resultant expressions can be most efiectively utilized by engineers for improved design, as they enable the calculation of the device's physical parameters, such as electrical to optical conversion e-ciency and emission angular distribution, as a function of de- vice structure. It should be pointed out that the incorporation of both rigorous electromagnetic analysis and coherence efiects is addressed in our report, to the best of our knowledge, for the flrst time. This results in a precise model capable of repeating and interpreting experimental and simulated data.

Measurements of the surface microroughness with the scanning electron microscope

A three-dimensional reconstruction system for scanning electron microscope consisting of a quadruple scintillator detector, a four-channel frame-grabber and PC-based processing unit was developed. The authors explored a method that takes advantage of the angular distribution of secondary electron emission to obtain quantitative topography contrast and surface profiles. Software processing algorithms were developed to carry out the reconstruction process and compensate for several types of errors, inherent in the method. After pre-calibration, the system allows obtaining surface topography with calculation of microroughness and waviness statistical parameters. The roughness estimation procedure was tested on metal roughness standards for machining and etched silicon surfaces. The main advantages of the system are almost real-time operation and reliable, composition-independent reconstruction for a broad class of materials.

Angular distribution and conversion of multi-keV L-shell X-ray sources produced from nanosecond laser irradiated thick-foil targets

AbstractAn experimental study on the angular distribution and conversion of multi-keV X-ray sources produced from 2 ns-duration 527nm laser irradiated thick-foil targets on Shenguang II laser facility (SG-II) is reported. The angular distributions measured in front of the targets can be fitted with the function of f(θ) = α+ (1−α)cosβθ (θ is the viewing angle relative to the target normal), where α = 0.41 ± 0.014, β = 0.77 ± 0.04 for Ti K-shell X-ray sources (~4.75 keV for Ti K-shell), and α = 0.085 ± 0.06, β = 0.59 ± 0.07 for Ag/Pd/Mo L-shell X-ray sources (2–2.8 keV for Mo L-shell, 2.8–3.5 keV for Pd L-shell, and 3–3.8 keV for Ag L-shell). The isotropy of the angular distribution of L-shell emission is worse than that of the K-shell emission at larger viewing angle (>70°), due to its larger optical depth (stronger self-absorption) in the cold plasma side lobe surrounding the central emission region, and in the central hot plasma region (emission region). There is no observable difference in the angular distributions of the L-shell X-ray emission among Ag, Pd, and Mo. The conversion efficiency of Ag/Pd/Mo L-shell X-ray sources is higher than that of the Ti K-shell X-ray sources, but the gain relative to the K-shell emission is not as high as that by using short pulse lasers. The conversion efficiency of the L-shell X-ray sources decreases with increasing atomic numbers (or X-ray photon energy), similar to the behavior of the K-shell X-ray source.

Nanoantenna array-induced fluorescence enhancement and reduced lifetimes

Enhanced fluorescence is observed from dye molecules interacting with optical nanoantenna arrays. Elliptical gold dimers form individual nanoantennae with tunable plasmon resonances depending upon the geometry of the two particles and the size of the gap between them. A fluorescent dye, Rhodamine 800, is uniformly embedded in a dielectric host that coats the nanoantennae. The nanoantennae act to enhance the dye absorption. In turn, emission from the dye drives the plasmon resonance of the antennae; the nanoantennae act to enhance the fluorescence signal and change the angular distribution of emission. These effects depend upon the overlap of the plasmon resonance with the excitation wavelength and the fluorescence emission band. A decreased fluorescence lifetime is observed along with highly polarized emission that displays the characteristics of the nanoantenna's dipole mode. Being able to engineer the emission of the dye–nanoantenna system is important for future device applications in both bio-sensing and nanoscale optoelectronic integration.

Dependence of AMSU-A Brightness Temperatures on Scattering From Antarctic Firn and Correlation With Polarization of SSM/I Data

A function of Advanced Microwave Sounding Unit-A (AMSU-A) measurements at 50.3 and 52.8 GHz is defined, which has the property of being sensitive to the angular distribution of surface-scattered atmospheric thermal emission but insensitive to the surface reflectivity, assuming reflectivity to be equal at the two frequencies. A scattering model consisting of a linear combination of specular reflection and Lambertian scattering is fitted to observed values of the function over Antarctica. The Lambertian fraction typically lies in the range of 0.7-1.0 with a mean of 0.84, and it is negatively correlated with polarization of the surface reflectivity, as determined from Special Sensor Microwave/Imager data. Dual-polarized 37-GHz measurements, combined with a separate measurement of the surface temperature, could be used as a predictor of the diffuseness of surface scattering when the atmospheric temperature profile is retrieved from measurements made by AMSU-A or a similar instrument, or when the radiances are assimilated for numerical weather prediction.

Single Molecule Studies in Chemical Biology and Nanosciences

Modern ultra-sensitive instrumental skill and expertise on surface modification of single biological molecules have sharpened the capabilities of scientists to address important current problems and explore new frontiers in many sci- entific disciplines including chemistry, molecular biology, molecular medicine and nano-structured materials. Develop- ment in single molecule studies (SMS) and manipulation (SMM) in the past two decades has unearthed very important in- formation hidden in chemical biology and nanosciences that was not possible earlier by ensemble measurements. For ex- ample, studying motion of biological motors like ATP synthase, DNA polymerase, RNA polymerase, etc could only be possible through single molecule manipulation. Single molecule fluorescence spectroscopy and studies could, for the first time directly show the surface dependent catalytic activities of a catalyst and angular distribution of emission of single chromophore unit. Estimation of step size of linear motors like myosin, kinesin, dynein, etc. was possible due to the de- velopment of single molecule fluorescence imaging with one nanometer accuracy and other techniques. Single molecule fluorescence resonance energy transfer could measure the distance between two moieties present in a single biomolecule and study the kinetics. Twisting DNA topoisomerase was directly observed by single molecule imaging technique. The dynamic properties of biomolecules through SMS have been expanding to DNA sequencing, sizing, conformational study, protein-DNA interaction, molecular motors, protein folding, conformational study, diffusion of single biomolecule in membrane, biomolecular reaction dynamics and single virus tracing etc. In this review our focus is to summarize some of the recent developments in single molecule studies and manipulation as mentioned above in chemical biology and nanosciences.

Single Molecule Studies in Chemical Biology and Nanosciences

Modern ultra-sensitive instrumental skill and expertise on surface modification of single biological molecules have sharpened the capabilities of scientists to address important current problems and explore new frontiers in many scientific disciplines including chemistry, molecular biology, molecular medicine and nano-structured materials. Development in single molecule studies (SMS) and manipulation (SMM) in the past two decades has unearthed very important information hidden in chemical biology and nanosciences that was not possible earlier by ensemble measurements. For example, studying motion of biological motors like ATP synthase, DNA polymerase, RNA polymerase, etc could only be possible through single molecule manipulation. Single molecule fluorescence spectroscopy and studies could, for the first time directly show the surface dependent catalytic activities of a catalyst and angular distribution of emission of single chromophore unit. Estimation of step size of linear motors like myosin, kinesin, dynein, etc. was possible due to the development of single molecule fluorescence imaging with one nanometer accuracy and other techniques. Single molecule fluorescence resonance energy transfer could measure the distance between two moieties present in a single biomolecule and study the kinetics. Twisting DNA topoisomerase was directly observed by single molecule imaging technique. The dynamic properties of biomolecules through SMS have been expanding to DNA sequencing, sizing, conformational study, protein-DNA interaction, molecular motors, protein folding, conformational study, diffusion of single biomolecule in membrane, biomolecular reaction dynamics and single virus tracing etc. In this review our focus is to summarize some of the recent developments in single molecule studies and manipulation as mentioned above in chemical biology and nanosciences.

The Five College Radio Astronomy Observatory CO Mapping Survey of the Taurus Molecular Cloud

The FCRAO Survey of the Taurus molecular cloud observed the 12CO and 13CO J = 1–0 emission from 98 deg2 of this important, nearby, star-forming region. This set of data with 45'' resolution comprises the highest spatial dynamic range image of an individual molecular cloud constructed to date and provides valuable insights to the molecular gas distribution, kinematics, and the star formation process. In this contribution, we describe the observations, calibration, data processing, and characteristics of the noise and line emission of the survey. The angular distribution of 12CO and 13CO emission over 1 km s−1 velocity intervals and the full velocity extent of the cloud are presented. These reveal a complex, dynamic medium of cold, molecular gas.

Two dimensional expansion effects on angular distribution of 13.5nm in-band extreme ultraviolet emission from laser-produced Sn plasma

The angular distribution of extreme ultraviolet emission at 13.5nm within 2% bandwidth was characterized for laser irradiated, planar, Sn targets at prototypic conditions for a lithography system. We have found that two dimensional plasma expansion plays a key role in the distribution of in-band 13.5nm emission under these conditions. The angular distribution was found to have two peaks at 45° and 15°. This complex angular distribution arises from the shape of both the emitting plasma and the surrounding absorbing plasma. This research reveals that the detailed angular distribution can be important to the deduction of conversion efficiency.

Extreme Ultraviolet Lithography Simulation by Tracing Photoelectron Trajectories in Resist

In order to evaluate the roughness of a resist pattern after development, photoelectron trajectories excited by extreme-ultraviolet (EUV) light are traced, and the resist pattern quality is discussed on the basis of a time-dependent resist development simulation. Binding energies of all subshells of atoms in poly(methyl methacrylate) (PMMA) and Si, and the photoionization cross section (dipole oscillator strength) are obtained by solving the Schrödinger equation with the Hartree–Fock–Slater potentials. The angular distribution of photoelectron emission is also taken into account. The photoelectron range from the generated position is around 30 nm in PMMA. If EUV light exposure has the square-wave intensity distribution, the critical dimension (CD) error and line edge roughness (LER) are almost negligible. If the aerial image is laterally sinusoidal, however, even if the contrast is unity, the pattern is seriously distorted. If the contrast is 0.5, the pattern is hardly formed for the doses less than 5.0 mJ/cm2.

Atomic-Layer Resolved Magnetic and Electronic Structure Analysis of Ni Thin Film on a Cu(001) Surface by Diffraction Spectroscopy

Up until now there has been no direct method for detecting the electronic and magnetic structure of each atomic layer at the surface, which is an essential analysis technique for nanotechnology. For this purpose, we have developed a new method, diffraction spectroscopy, based on the photon energy dependence of the angular distribution of Auger electron emission. We have applied this method to analyze the magnetic structure of a Ni ultrathin film on a Cu(001) surface around the spin reorientation transition. Atomic-layer resolved x-ray absorption and magnetic circular dichroism spectra were obtained. Surface and interior core-level shifts and magnetic moments are determined for each atomic layer individually.

Photoluminescence emission profiles of Y_2O_3:Eu films composed of high-low density stacks produced by glancing angle deposition

Periodic high-/low-index film stacks composed of Y(2)O(3) : Eu were grown by glancing angle deposition on silicon and fused silica substrates. Postdeposition annealing at temperatures from 600 to 1000 degrees C for 1 h in air was performed to activate photoluminescence. Absolute photoluminescence spectra were obtained as a function of observation angle. The angular emission distribution was non-Lambertian, with peak emission at angles of 50 to 60 degrees with respect to substrate normal. Spectroscopic transmittance and ellipsometry measurements were performed to characterize the films. Using this description, we were able to reproduce the angular photoluminescence patterns of the films.