Frequency offsets in frequency-locked semiconductor lasers

A commonly used technique for frequency locking a laser is dithering the laser frequency and monitoring the first derivative of the laser transmission through an absolute reference. In semiconductor lasers, this frequency dithering can be obtained easily by dithering the injection current. However, this dithering also modulates the laser output power. Here we show that this modulation of the laser output power results in an offset of the locked laser frequency from the reference frequency. We derive analytical expressions for these frequency offsets for semiconductor lasers frequency-locked to a Fabry-Perot transmission peak, a Gaussian absorption line, and a Lorentzian absorption line.     

Energy band structure of I–III–VI2 semiconductors

We review recent studies of the energy band structure of I-III-VI₂ semiconductors. The structure of the uppermost valence bands of a I-III-VI₂ compound is profoundly influenced by the proximity of noble metal d levels in the valence band. The direct energy gaps observed in I-III-VI₂ compounds are low relative to the energy gaps in the II–VI analogs by amounts up to 1.6eV, and the spin-orbit splittings observed in the ternaries are low relative to the values observed in the binary analogs, owing to a partial cancellation of the positive spin-orbit parameter for p levels and the negative spin-orbit parameter for d levels. The presence of the noble metal d levels in the valence band has been confirmed directly by the observation of electroreflectance structure due to transitions from the d levels themselves to the lowest conduction band minimum.     

Reversible and persistent electrical bistability in single crystals of a self-assembled pi-conjugated tetraaryl system: a submicrometer scale electrical characterization

A new pi-conjugated electroactive 4,4'-bipyridinium that bears two pyridazone self-complementary units was prepared and characterized. The new system readily assembles and forms at least two stable charge-transfer crystalline structures having a thermal population of unpaired electrons. The crystals of one phase exhibit electrical bistability, displaying either high (ON) and low (OFF) conductivity, at the same applied bias, depending on the electrical history of the system. The relation between the supramolecular structure of the crystals and their electrical properties is also discussed.     

A Note on Average-Case Sorting

This note studies the average-case comparison-complexity of sorting n elements when there is a known distribution on inputs and the goal is to minimize the expected number of comparisons. We generalize Fredman’s algorithm which is a variant of insertion sort and provide a basically tight upper bound: If μ is a distribution on permutations on n elements, then one may sort inputs from μ with expected number of comparisons that is at most H(μ) + 2n, where H is the entropy function. The algorithm uses less comparisons for more probable inputs: For every permutation π, the algorithm sorts π by using at most \(\log _{2}(\frac {1}{\Pr _{\mu }(\pi )})+2n\) comparisons. A lower bound on the expected number of comparisons of H(μ) always holds, and a linear dependence on n is also required.     

Three-species collisionless reconnection: effect of O+ on magnetotail reconnection

The nature of collisionless reconnection in a three-species plasma composed of a heavy species, protons, and electrons is examined. In addition to the usual two length scales present in two-species reconnection, there are two additional larger length scales in the system: one associated with a "heavy whistler" which produces a large scale quadrupolar out-of-plane magnetic field, and one associated with the "heavy Alfvén" wave which can slow the outflow speed and thus the reconnection rate. The consequences for reconnection with O+ present in the magnetotail are discussed.     

Ion debris mitigation from tin plasma using ambient gas,magnetic field and combined effects

Mitigation of energetic ions from laser produced tin plasma is one of the principal issues in the development of an extreme ultraviolet lithographic light source. We explored the possibility of using an ambient gas and/or a magnetic field for controlling the energetic ions from tin plasma. Hydrogen, helium and argon gases provide good transmission to 13.5 nm and are found to be an effective stopper for tin ions. Absorption of in-band radiation limits the density of gas below levels needed to completely protect optics. Tin ion ranges in buffer gases were estimated using the Monte Carlo simulation code SRIM and compared with experimental results. The presence of a moderate transverse magnetic field of 0.64 T slowed the propagation of fast moving tin ions but failed to stop them. The synergistic effect of a combination of magnetic field and an ambient gas is found to be very promising for mitigating tin ions without exceeding EUV gas absorption limits. PACS 42.72.Bj; 52.50.Jm; 52.55.Jd; 52.70.kz     

LCD motion blur reduction: a signal processing approach.

Liquid crystal displays (LCDs) have shown great promise in the consumer market for their use as both computer and television displays. Despite their many advantages, the inherent sample-and-hold nature of LCD image formation results in a phenomenon known as motion blur. In this work, we develop a method for motion blur reduction using the Richardson-Lucy deconvolution algorithm in concert with motion vector information from the scene. We further refine our approach by introducing a perceptual significance metric that allows us to weight the amount of processing performed on different regions in the image. In addition, we analyze the role of motion vector errors in the quality of our resulting image. Perceptual tests indicate that our algorithm reduces the amount of perceivable motion blur in LCDs.     

Filter banks for improved LCD motion

In the past several years much attention has been placed on improving the motion picture quality of liquid crystal displays (LCDs). One pervasive problem is motion blur which occurs due to the inherent sample-and-hold nature of LCD image formation. In this work, we take a signal processing approach to motion blur reduction by pre-processing the data before it is sent to the display. We develop a two-channel non-perfect reconstruction filter bank that is able to reduce the amount of perceivable motion blur. In addition, as in similar works, we discriminate between different regions of the scene and weight the application of the algorithm based on their susceptibility to motion blur. Perceptual tests indicate that our algorithm reduces the amount of perceivable motion blur on LCDs.     

An Integrated Assessment of the Impacts of Hydrogen Economy on Transportation, Energy Use, and Air Emissions

This paper presents an analysis of the potential system-wide energy and air emissions implications of hydrogen fuel cell vehicle (H ₂-FCV) penetration into the U.S. light duty vehicle (LDV) fleet. The analysis uses the U.S. EPA MARKet ALlocation (MARKAL) technology database and model to simultaneously consider competition among alternative technologies and fuels, with a focus on the transportation and the electric sectors. Our modeled reference case suggests that economics alone would not yield H₂-FCV penetration by 2030. A parametric sensitivity analysis shows that H₂-FCV can become economically viable through reductions in H ₂-FCV costs, increases in the costs of competing vehicle technologies, and increases in oil prices. Alternative scenarios leading to H₂-FCV penetration are shown to result in very different patterns of total system energy usage depending on the conditions driving H₂-FCV penetration. Overall, the model suggests that total CO₂ emissions changes are complex, but that CO₂ emission levels tend to decrease slightly with H₂-FCV penetration. While carbon capture and sequestration technologies with H ₂ production and renewable technologies for H₂ production have the potential to achieve greater CO₂ reductions, these technologies are not economically competitive within our modeling time frame without additional drivers     

Growing ZnO crystals on magnetite nanoparticles

We report herein on the oriented growth of ZnO crystals on magnetite nanoparticles. The ZnO crystals were grown by hydrolyzing a supersaturated aqueous solution of zinc nitrate. The seeds for the growth were magnetite nanoparticles with a diameter of 5.7 nm and a narrow size distribution. Hollowed ZnO hexagons of 0.15 microm width and 0.5 microm length filled with Fe(3)O(4) particles were obtained. HR-TEM (high-resolution transmission electron microscopy) and selected-area EDS (energy-dispersive spectroscopy) show that the nanoparticles are homogenously spread in the ZnO tubes. Zeta potential measurements were employed to understand the relationship between the nanoparticles and the oriented growth of the ZnO crystals. The results show that the surfactants induced the directional growth of the ZnO crystals.