Biomedical subjects

J L Reno

Publications and source records attributed to J L Reno.

7 recordsLinked to original sources

PubMed2006

Antenna model for wire lasers.

An antenna model is proposed for long (L >> A) lasers with subwavelength cross sections (wire lasers). It is shown that the far-field pattern of the wire lasers is determined by the ratio of the wavelength to the length. The radiation of the wire laser is predicted to be concentrated in a narrow beam theta approximately radical(2lambda/L) for laser modes where the longitudinal phase velocity is in synchronism with the velocity of light in air. Experimental results obtained using a terahertz quantum cascade wire laser are in agreement with the model.

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PubMed2005

Frequency and phase-lock control of a 3 THz quantum cascade laser.

We have locked the frequency of a 3 THz quantum cascade laser (QCL) to that of a far-infrared gas laser with a tunable microwave offset frequency. The locked QCL line shape is essentially Gaussian, with linewidths of 65 and 141 kHz at the -3 and -10 dB levels, respectively. The lock condition can be maintained indefinitely, without requiring temperature or bias current regulation of the QCL other than that provided by the lock error signal. The result demonstrates that a terahertz QCL can be frequency controlled with 1-part-in-10(8) accuracy, which is a factor of 100 better than that needed for a local oscillator in a heterodyne receiver for atmospheric and astronomic spectroscopy.

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PubMed2005

Two-dimensional metal-insulator transition as a percolation transition in a high-mobility electron system.

By carefully analyzing the low temperature density dependence of 2D conductivity in undoped high-mobility n-GaAs heterostructures, we conclude that the 2D metal-insulator transition in this 2D electron system is a density inhomogeneity driven percolation transition due to the breakdown of screening in the random charged impurity disorder background. In particular, our measured conductivity exponent of approximately 1.4 approaches the 2D percolation exponent value of 4/3 at low temperatures and our experimental data are inconsistent with there being a zero-temperature quantum critical point in our system.

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PubMed2004

Oscillatory magnetothermopower and resonant phonon drag in a high-mobility 2D electron gas.

Experimental and theoretical evidence is presented for new low-magnetic-field (B<5 kG) 1/B oscillations in the thermoelectric power of a high-mobility GaAs/AlGaAs two-dimensional (2D) electron gas. The oscillations result from inter-Landau-level resonances of acoustic phonons carrying a momentum equal to twice the Fermi wave number at B=0. Numerical calculations show that both 3D and 2D phonons can contribute to this effect.

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PubMed2003

Resistivity of dilute 2D electrons in an undoped GaAs heterostructure.

We report resistivity measurements from 0.03 to 10 K in a dilute high mobility 2D electron system. Using an undoped GaAs/AlGaAs heterojunction in a gated field-effect transistor geometry, a wide range of densities, 0.16 x 10(10) to 7.5 x 10(10) cm(-2), are explored. For high densities, the results are quantitatively shown to be due to scattering by acoustic phonons and impurities. In an intermediate range of densities, a peak in the resistivity is observed for temperatures below 1 K. This nonmonotonic resistivity can be understood by considering the known scattering mechanisms of phonons, bulk, and interface ionized impurities. Still lower densities appear insulating to the lowest temperature measured.

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PubMed2002

Zener tunneling between landau orbits in a high-mobility two-dimensional electron gas.

Magnetotransport in a laterally confined two-dimensional electron gas (2DEG) can exhibit modified scattering channels owing to a tilted Hall potential. Transitions of electrons between Landau levels with shifted guiding centers can be accomplished through a Zener tunneling mechanism, and make a significant contribution to the magnetoresistance. A remarkable oscillation effect in weak field magnetoresistance has been observed in high-mobility 2DEGs in GaAs -Al Ga 0.3As (0.7) heterostructures, and can be well explained by the Zener mechanism.

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PubMed2001

New class of magnetoresistance oscillations: interaction of a two-dimensional electron gas with leaky interface phonons.

We report on a new class of magnetoresistance oscillations observed in a high-mobility two-dimensional electron gas (2DEG) in GaAs-Al(x)Ga(1--x)As heterostructures. Appearing in a weak magnetic field ( B < 0.3 T) and only in a narrow temperature range ( 2 K < T < 9 K), these oscillations are periodic in 1/B with a frequency proportional to the electron Fermi wave vector, k(F). We interpret the effect as a magnetophonon resonance of the 2DEG with leaky interface-acoustic phonon modes carrying a wave vector q = 2k(F). Calculations show a few branches of such modes existing on the GaAs-Al(x)Ga(1--)xAs interface, and their velocities are in quantitative agreement with the observation.

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