A statistical approach is taken toward the ray optics of optical media with complicated nonspherical and nonplanar surface shapes. As a general rule, the light in such a medium will tend to be randomized in direction and of 2n2(x) times greater intensity than the externally incident light, where n(x) is the local index of refraction. A specific method for doing optical calculations in statistical ray optics will be outlined. These optical enhancement effects can result in a new type of antireflection coating. In addition, these effects can improve the efficiency as well as reduce the cost of solar cells.
Tracing the negative resistance characteristics of 2-terminal and 3-terminal devices often ended in failure due to jump phenomenon, hysteresis, and oscillation resulting from the tracing circuit. All of these problems are overcome in the curve tracer described in this paper. A detailed nonlinear dynamic circuit analysis is used to develop a simple method for quenching oscillations and other exotic phenomena. Our curve tracer is designed to trace either voltage-controlled or current-controlled negative resistance characteristics of both 2-terninal and 3-terminal devices. All six representations which completely characterized a 3-terminal or 2-port nonlinear resistor are allowed. In particular, using a novel approach for implementing a nullator and norator, transmission (chain) characteristics of 3-terminal and 2-port devices have been successfully traced for the first time.
Experimental confirmation has been made on a driven relaxation oscillator circuit, first presented by Van der Pol, of the periodadding route to chaos. The nonlinear element in the circuit is a neon bulb, modeled by a three-segment piecewise-linear current-controlled resistor. A simple nonlinear circuit model has been used to reproduce in simulations the experimentally-observed period-adding phenomenon.
Non-interpenetrating two star polymer catalysts designed to mimic the site isolation characteristics of enzymes enabled a one-pot asymmetric cascade reaction. Thus, the one-pot nucleophilic addition of 2 to 1 and Michael addition of the resulting 3 to 4 were performed with a star polymer salt catalyst 6˙7 (20 mol%) [prepared from an acidic star polymer 6 and imidazolidinone (S,S)-7], a pyrrolidine star polymer (S)-8 (20 mol%), and a catechol mediator 9 (1 mol equiv) to give ( R,S )-5 in 89% yield with >99% ee and 96% de. The use of 10 or 11 in place of 6 or 8 under similar conditions did not give 5.
Evidence is reported for a nonrandom process by which laser-produced plasmas emit suprathermal electrons. Emission is dominated by a 1 to 2 psec monoenergetic burst, during which the electron energy decreases rapidly. The suprathermal tail on the energy distribution is due to the integrated temporal variation of the electron energy, not to statistical processes. The hot-electron temperature thus produced is practically independent of laser pulse energy.
Two different bifurcation patterns are experimentally observed in Chua's circuit. They show that antimonotonicity — inevitable reversals of period-doubling sequences, is a typical phenomenon in Chua's circuit.
Utilizing synchronized 50 ps pulses from two independently tunable CO2 lasers, a pump–probe experiment is performed on pentafluorobenzene. The molecule, which has two infrared active modes accessible to the CO2 laser wavelengths, allows an extensive investigation into the statistical nature of the intramolecular vibrational energy relaxation process. We find discrete state effects, indicated by oscillatory behavior in the time-resolved absorption spectrum, disappear when the molecule is heated into the quasicontinuum. Using the anharmonic redshifting and broadening of the normal mode absorption features in the infrared spectrum as a measure of local temperature, our results indicate rapid equilibration (<50 ps) of absorbed energy among modes, with the final distribution of energy consistent with thermal heating.
Non-interpenetrating star polymer catalysts designed to mimic the site isolation characteristics of enzymes enable the one-pot combination of multiple otherwise incompatible catalysts for asymmetric cascade reactions that involve iminium, enamine, and H-bonding catalysis. Control experiments replacing star polymer catalysts with the corresponding small molecule or linear polymer analogues lead to little or no cascade reaction. Our strategy also allows straightforward access to all possible stereoisomers of the cascade product individually by proper choice of catalyst chirality. To our knowledge, this work represents the most sophisticated study of soluble polymers for site isolation, enzyme-like catalysis that generates cascade products with multiple chiral centers.
Fluxes of carbon dioxide, water vapor, sensible heat, and momentum obtained over the boreal forest from the Twin Otter aircraft and six tower‐based systems are compared. These measurements were collected as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS) during three intensive field campaigns between May 25 and September 17, 1994. The representativeness of the tower‐based measurements collected during BOREAS is discussed. Even though the net radiation from aircraft‐ and tower‐based systems agreed well, in general, the aircraft tended to observe larger latent heat and smaller sensible heat fluxes than the towers. The CO 2 fluxes from the aircraft were substantially less than from the tower, while the differences were relatively small for the momentum fluxes. The relationships between aircraft and tower‐based flux measurements obtained by making repeated runs past various towers are used to scale up tower‐based fluxes to a 16×16 km 2 area near Prince Albert, Saskatchewan. It is demonstrated that except for a couple of cases primarily due to rapidly changing radiation conditions, this combination of measurements provides regional flux estimates of momentum, CO 2 , and sensible and latent heat similar to those obtained by flying a grid pattern over the area.
The objective of this program is to make infrared pigments whose emissivity can be controlled. The principal approach we have taken is to make 3-dimensionally microstructured metallodielectric materials by two-photon lithography in photoresist, and back-filling with metals. In this program we demonstrated that we can quickly and efficiency fabricate 3<1 microstructures in photoresist using a diode pumped Ti-sapphire modelocked laser in combination with a mechanical scanning technology. Metal back-filling of copper into porous membranes was accomplished using electrodeposition methods and complementary fundamental studies were able to establish some of the details of this metallization process. Initial results using self-assembly methods for metallization were also obtained. Another approach for producing 3<1 metallo-dielectric structures, based on the direct writing of silver structures by two-photon processes, was also demonstrated. In addition to experimental work, this program included computational activities. An analysis of the resolution limits of two-photon lithography showed that a doubling of resolution was possible. Other studies in this program included the design of frequency selective grid structures and an analysis showing that 1-d interference filters can be used to achieve a broad reflection spectrum.
Development in the WDM technologies has made multi-wavelength optical sources and components available. By combining WDM mux-demux and fast electro-optic switches, a fast configurable WDM add-drop filter can be obtained. This enables using WDM with TDM in a way that each TDM time slot is also wavelength multiplexed. Hence introducing a second dimension for switching in addition to the time dimension. This also alleviates the demanding requirement on TDM as the switching throughput increases. The number of channels that can be supported in a WDM/TDM hybrid switching system is the product of the number of time slots and the number of available wavelengths. We have done preliminary analysis on the system throughput. We will present implementation considerations of the above described systems, the give the comparison on the throughput and security sides.
Read moreWe present an optical tandem single-sideband receiver that enables the detection of signals having different information in the two sidebands of the same optical carrier. The technique relies on the use of a dual-electrode Mach-Zehnder modulator and achieves heterodyne detection without the use of an optical local oscillator. Sharp filtering requirements are met in the electrical domain, eliminating the need for wasteful guardbands.
Read moreWe describe how quantum information may be transferred from photon polarization to electron spin in a semiconductor device. The transfer of quantum information relies on selection rules for optical transitions, such that two superposed photon polarizations excite two superposed spin states. Entanglement of the electron spin state with the spin state of the remaining hole is prevented by using a single, non-degenerate initial valence band. The degeneracy of the valence band is lifted by the combination of strain and a static magnetic field. We give a detailed description of a semiconductor structure that transfers photon polarization to electron spin coherently, and allows electron spins to be stored and to be made available for quantum information processing.
Read moreWe derive an exact formula for the decomposition of Gaussian spatially averaged experimental data. The true nonlinear functional dependence of a physical parameter on the local light intensity can be obtained.
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