Physics Commons^™

Degenerate Parallel Conducting Layer And Conductivity Type Conversion Observed From P-Ge1 - YSnY (Y = 0.06%) Grown On N-Si Substrate, Mee-Yi Ryu, Yung Kee Yeo, M. Ahoujja, Thomas R. Harris, Richard T. Beeler, John Kouvetakis

Faculty Publications

Electrical properties of p-Ge_1−ySn_y (y = 0.06%) grown on n-Si substrate were investigated through temperature-dependent Hall-effect measurements. It was found that there exists a degenerate parallel conducting layer in Ge_1−ySn_y/Si and a second, deeper acceptor in addition to a shallow acceptor. This parallel conducting layer dominates the electrical properties of the Ge_1−ySn_y layer below 50 K and also significantly affects those properties at higher temperatures. Additionally, a conductivity type conversion from p to n was observed around 370 K for this sample. A two-layer conducting model was used …

Serpentine Low Loss Trapezoidal Silica Waveguides On Silicon, Xiaomin Zhang, Mark Harrison, Audrey Harker, Andrea M. Armani

Engineering Faculty Articles and Research

We report the fabrication and characterization of straight and serpentine low loss trapezoidal silica waveguides integrated on a silicon substrate. The waveguide channel was defined using a dual photo-lithography and buffered HF etching and isolated from the silicon substrate using an isotropic silicon etchant. The waveguide is air-clad and thus has a core-cladding effective index contrast of approximately 25%. Measured at 658, 980 and 1550nm, the propagation loss was found to be 0.69, 0.59, and 0.41dB/cm respectively, with a critical bending radius less than 375μm. The waveguide’s polarization behavior was investigated both theoretically and experimentally. Additionally, the output power shows …

Commissioning Of The Asta Laser Lab With Uv Pulse Length Characterization, Daniel Kelley, Jeff Corbett

STAR Program Research Presentations

The Linac Coherent Light Source (LCLS) at SLAC depends on a photocathode electron gun to provide the linear accelerator with the raw material – electrons – used for making X-ray laser pulses. The photocathode used in the LCLS Injector is a clean copper plate in high vacuum. When the cathode is struck with high energy UV light, electrons are liberated from its surface and then accelerated down the linac with radio-frequency electric fields. These fast-moving bunches of electrons are directed through an undulator magnet to radiate X-ray light.

Although scientists have been using photocathode techniques at SLAC for 25 years, …

Spectral Analysis Of Encrypted Chaotic Signals Using Fast Fourier Transforms And Laboratory Spectral Analyzers, Monish Ranjan Chatterjee, Abhinay Kundur

Electrical and Computer Engineering Faculty Publications

The use of acousto-optic chaos, as manifested via first-order feedback in an acousto-optic Bragg cell, in encrypting a message wave and subsequently recovering the message in the receiver using a chaotic heterodyne strategy, has been reported recently [1-3]. In examining the dynamical system analytically using computer simulation, (expected) modulated chaos waveforms are obtained within specified observation windows.

Because of the relatively random nature inherent in chaos waveforms, it is essentially impossible to ascertain from the visual display of the chaotic wave whether a given message signal has in fact modulated the chaotic "carrier". In fact, it has been observed from …

Dynamical Model Of Harmonic Generation In Centrosymmetric Semiconductors At Visible And Uv Wavelengths, Michael Scalora, Maria Antonietta Vincenti, Domenico De Ceglia, N. Akozbek, Vito Roppo, M. J. Bloemer, Joseph W. Haus

Electrical and Computer Engineering Faculty Publications

We study second and third harmonic generation in centrosymmetric semiconductors at visible and UV wavelengths in bulk and cavity environments. Second harmonic generation is due to a combination of spatial symmetry breaking, the magnetic portion of the Lorentz force, and quadrupolar contributions from inner core electrons. The material is assumed to have a nonzero, third-order nonlinearity that gives rise to most of the third harmonic signal. Using the parameters of bulk silicon we predict that cavity environments modify the dependence of second harmonic generation on incident angle, while improving third harmonic conversion efficiency by several orders of magnitude relative to …

Information Encryption And Retrieval In Mid-Rf Range Using Acousto-Optic Chaos, Monish Ranjan Chatterjee, Abhinay Kundur

Electrical and Computer Engineering Faculty Publications

In recent work, low-frequency AC signal encryption, decryption and retrieval using system-parameter based keys at the receiver stage of an acousto-optic (A-O) Bragg cell under first-order feedback have been demonstrated [1,2]. The corresponding nonlinear dynamics have also been investigated using the Lyapunov exponent and the so-called bifurcation maps [3]. The results were essentially restricted to A-O chaos around 10 KHz, and (baseband) signal bandwidths in the 1-4 KHz range. The results have generally been satisfactory, and parameter tolerances (prior to severe signal distortion at the output) in the ±5% - ±10% range have been obtained.

Periodic AC waveforms, and a …

Low-Loss Meta-Atom For Improved Resonance Response, Derrick Langley, Ronald Coutu Jr., Peter J. Collins

Faculty Publications

Measurements of a meta-atom integrated with a low noise amplifier into the split-ring resonator are presented. A comparison is made between baseline meta-atoms and one integrated with a GaAs low noise amplifier. S-parameter measurements in a RF strip-line show the resonant frequency location. The resonance null is more prominent for the integrated meta-atom. Biasing the low noise amplifier from 0 to 7 VDC showed that the resonant null improved with biasing voltage. As the biasing voltage increases, the transmission null reduced from -11.82 to -23.21 dB for biases from 0 to 7 VDC at resonant frequency.

A Threshold-Based Approach To Calorimetry In Helium Droplets: Measurement Of Binding Energies Of Water Clusters, William K. Lewis, Barbara A. Harruff-Miller, Michael A. Gord, Joseph R. Gord, Elena A. Guliants, Christopher E. Bunker

Electrical and Computer Engineering Faculty Publications

Helium dropletbeam methods have emerged as a versatile technique that can be used to assemble a wide variety of atomic and molecular clusters. We have developed a method to measure the binding energies of clusters assembled in helium droplets by determining the minimum droplet sizes required to assemble and detect selected clusters in the spectrum of the dopeddropletbeam. The differences in the droplet sizes required between the various multimers are then used to estimate the incremental binding energies. We have applied this method to measure the binding energies of cyclic waterclusters from the dimer to the tetramer. We obtain measured …

Time Dynamics Of Self-Pumped Reflection Gratings In A Photorefractive Polymer, Partha P. Banerjee, S. H. Buller, C. M. Liebig, S. A. Basun, Gary Cook, Dean R. Evans, Pierre-Alexandre Blanche, J. Thomas, Cory W. Christenson, N. Peyghambarian

Electrical and Computer Engineering Faculty Publications

The time dynamics of self-pumped reflection gratings in a commonly used photorefractive polymer PDCST:PVK:ECZ-BBP:C60 with no additional electron sources or traps is investigated. While holes are normally the mobile charges and responsible for grating formation, our experimental observations, analyzed using multi-exponential fitting curves, show evidence of electrons in addition to holes as charge carriers, particularly above an applied field of 40 V/μm.

The dependence of effective carrier mobilities on the applied electric field, deduced from experimental results, show stronger field dependence of electron mobility at high electric fields. At an applied field of 70 V/μm, electron and hole mobilities become …

Examination Of The Nonlinear Dynamics Of A Chaotic Acousto-Optic Bragg Modulator With Feedback Under Signal Encryption And Decryption, Mohammed A. Al-Saedi, Monish Ranjan Chatterjee

Electrical and Computer Engineering Faculty Publications

An acousto-optic Bragg cell with first-order feedback, which exhibits chaotic behavior past the threshold for bistability, was recently examined for possible chaotic encryption and recovery of simple messages (such as low-amplitude periodic signals) applied via the bias input of the sound cell driver. We carry out a thorough examination of the nonlinear dynamics of the Bragg cell under intensity feedback for (i) dc variations of the feedback gain (β˜) and the phase shift parameter (α^ 0) and (ii) ac variations of α^ 0; total under signal encryption, investigating both from two different perspectives: (i) examining chaos in view of the …

Commentary And Interpretations Of Tagore’S 'Ode To Africa', Monish Ranjan Chatterjee

Electrical and Computer Engineering Faculty Publications

This is a commentary/interpretation of Rabindranath Tagore's poem "Ode to Africa."