3,088 research outputs found
A theoretical and experimental investigation of the modes of optical resonators with phase-conjugate mirrors
We present an analysis of resonator properties for a cavity bounded by a phase conjugate mirror, which is generated by a degenerate four-wave nonlinear optical interaction. Using a ray matrix formalism to describe the conjugate mirror, resonator stability conditions are derived. Longitudinal and transverse mode characteristics are discussed. Results are compared with an experiment where laser oscillation was observed at 6943 Å using carbon disulfide as the nonlinear interacting medium comprising the phase conjugate mirror
Excimer lasers
The results of a two-year investigation into the possibility of developing continuous wave excimer lasers are reported. The program included the evaluation and selection of candidate molecular systems and discharge pumping techniques. The K Ar/K2 excimer dimer molecules and the xenon fluoride excimer molecule were selected for study; each used a transverse and capillary discharges pumping technique. Experimental and theoretical studies of each of the two discharge techniques applied to each of the two molecular systems are reported. Discharge stability and fluorine consumption were found to be the principle impediments to extending the XeF excimer laser into the continuous wave regime. Potassium vapor handling problems were the principal difficulty in achieving laser action on the K Ar/K2 system. Of the four molecular systems and pumping techniques explored, the capillary discharge pumped K Ar/K2 system appears to be the most likely candidate for demonstrating continuous wave excimer laser action primarily because of its predicted lower pumping threshold and a demonstrated discharge stability advantage
Spin-dependent transport in a quasiballistic quantum wire
We describe the transport properties of a 5 m long one-dimensional (1D)
quantum wire. Reduction of conductance plateaux due to the introduction of
weakly disorder scattering are observed. In an in-plane magnetic field, we
observe spin-splitting of the reduced conductance steps. Our experimental
results provide evidence that deviation from conductance quantisation is very
small for electrons with spin parallel and is about 1/3 for electrons with spin
anti-parallel. Moreover, in a high in-plane magnetic field, a spin-polarised 1D
channel shows a plateau-like structure close to which
strengthens with {\em increasing} temperatures. It is suggested that these
results arise from the combination of disorder and the electron-electron
interactions in the 1D electron gas.Comment: 4 pages, 5 figures, latex to be published in Phys. Rev. B (15/3/2000
Anomalous spin-dependent behaviour of one-dimensional subbands
We report a new electron interaction effect in GaAs/AlGaAs quantum wires.
Using DC-bias spectroscopy, we show that large and abrupt changes occur to the
energies of spin-down (lower energy) states as they populate. The effect is not
observed for spin-up energy states. At B=0, interactions have a pronounced
effect, in the form of the well-known 0.7 Structure. However, our new results
show that interactions strongly affect the energy spectrum at all magnetic
fields, from 0 to 16T, not just in the vicinity of the 0.7 Structure.Comment: 4 pages, 2 figure
Coulomb-Blockade directional coupler
A tunable directional coupler based on Coulomb Blockade effect is presented.
Two electron waveguides are coupled by a quantum dot to an injector waveguide.
Electron confinement is obtained by surface Schottky gates on single
GaAs/AlGaAs heterojunction. Magneto-electrical measurements down to 350 mK are
presented and large transconductance oscillations are reported on both outputs
up to 4.2 K. Experimental results are interpreted in terms of Coulomb Blockade
effect and the relevance of the present design strategy for the implementation
of an electronic multiplexer is underlined.Comment: 4 pages, 4 figures, to be published in Applied Physics Letter
Possible evidence of a spontaneous spin-polarization in mesoscopic 2D electron systems
We have experimentally studied the non-equilibrium transport in low-density
clean 2D electron systems at mesoscopic length scales. At zero magnetic field
(B), a double-peak structure in the non-linear conductance was observed close
to the Fermi energy in the localized regime. From the behavior of these peaks
at non-zero B, we could associate them to the opposite spin states of the
system, indicating a spontaneous spin polarization at B = 0. Detailed
temperature and disorder dependence of the structure shows that such a
splitting is a ground state property of the low-density 2D systems.Comment: 7 pages, 5 figure
Assessing Learning Outcomes in Middle-Division Classical Mechanics: The Colorado Classical Mechanics/Math Methods Instrument
Reliable and validated assessments of introductory physics have been
instrumental in driving curricular and pedagogical reforms that lead to
improved student learning. As part of an effort to systematically improve our
sophomore-level Classical Mechanics and Math Methods course (CM 1) at CU
Boulder, we have developed a tool to assess student learning of CM 1 concepts
in the upper-division. The Colorado Classical Mechanics/Math Methods Instrument
(CCMI) builds on faculty consensus learning goals and systematic observations
of student difficulties. The result is a 9-question open-ended post-test that
probes student learning in the first half of a two-semester classical mechanics
/ math methods sequence. In this paper, we describe the design and development
of this instrument, its validation, and measurements made in classes at CU
Boulder and elsewhere.Comment: 11 pages, 6 figures, 1 tabl
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