Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session N13: Devices and Applications I |
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Sponsoring Units: FIAP Chair: Alan Todd, Advanced Energy Systems Room: LACC 402B |
Wednesday, March 23, 2005 8:00AM - 8:12AM |
N13.00001: The Influence of Dielectric Imperfections on the Optical Properties of 1D and 2D Photonic Crystal Structures Karlene Maskaly, W. Craig Carter, James Maxwell, Richard Averitt Both 1D and 2D photonic crystals have become extremely useful tools in the optics industry due to the presence of wavelength-tunable photonic band gaps. However, little is known about the optical effects of dielectric imperfections, such as interfacial roughness, in the geometry of these structures. We have employed a Finite Difference Time Domain (FDTD) code to explore this problem and gain further insight into the effect of such imperfections on the optical properties of both 1D and 2D photonic crystal geometries. Imperfections that have been explored include: interfacial roughness and surface scratches in 1D photonic crystals, and aspherical holes in 2D photonic crystal structures. We present the effects of these imperfections on the reflectivity of the photonic crystal structures for wavelengths corresponding to the perfect structures' photonic band gap. We also provide a parameterized fit to quantify the results and aid in tolerance estimations. [Preview Abstract] |
Wednesday, March 23, 2005 8:12AM - 8:24AM |
N13.00002: The effect of the Crystal Geometry and Photorefraction to Electro-optic field sensors Dong Ho Wu, Anthony Garzarella For the development of electro-optic (EO) field sensors we have investigated the EO response of several Lithium Niobate and Strontium Barium Niobate crystals. The EO responsivity is greatly affected by the spatial variation of the refractive index induced by the photorefractive effects. For a Lithium Niobate crystal, with which the photorefractive effect is negligibly small, the detector output signals could be accurately modeled by assuming a beam of coherent phase. For a strongly photorefractive Strontium Barium Niobate crystals, we need to modify the model using a distribution function for the phase of polarization to reconcile our model with the data. Such distributions were evident through spatial-temporal instabilities of the detector signals. While the modeled distribution of the polarization phase which fits the data corresponds to refractive index variations of only 10$^{-5}$, the impact on the EO detector sensitivity can be devastating. We will discuss our detailed experimental results on the EO and photorefractive materials. [Preview Abstract] |
Wednesday, March 23, 2005 8:24AM - 8:36AM |
N13.00003: Strain Induced Switching of Magnetostrictive Dot Arrays M.-T. Bootsmann, S. Dokupil, M. L\"ohndorf For further miniaturization of magnetostrictive TMR strain sensors [1], it is necessary to analyze the switching properties of the magnetostrictive free layers under mechanical strain. Therefore, we have combined MEMS and thin-film technologies in order to fabricate highly magnetostrictive FeCo and amorphous CoFeSiB micro-/ nano-dot arrays on 0.5-1$\mu $m thick Si3N4-membranes with diameters of 50 to 300$\mu $m. By applying variable pressure to the membrane the dot arrays were exposed to compressive or tensile strain. MFM as well as MOKE measurements have been applied to resolve the micromagnetic structures and the corresponding hysteresis loops for different levels of applied mechanical strain. For 1$\mu $m CoFeSiB dots we observed a multi-domain state under stress free condition, whereas for 0.01{\%} of tensile strain a single domain behavior has been observed with an alignment of the magnetization parallel to the strain direction. By changing to compressive strain the domains are rotated by 90\r{ } leading to a magnetization perpendicular to the strain direction as expected for positive magnetostrictive materials. [1] M. L\"{o}hndorf et al. APL 81(2), 313 (2002) [Preview Abstract] |
Wednesday, March 23, 2005 8:36AM - 8:48AM |
N13.00004: Minimizing 1/f Noise in Magnetic Sensors with a MEMS Flux Concentrator Alan Edelstein, Greg Fischer, Jeff Pulskamp, Michael Petersen, William Bernard, Shu Fan Cheng, Cathy Nordman The performance of magnetic sensors at frequencies on the order of 1 Hz is generally limited by $1/f $noise and the fact that the signal is small relative to the DC background. We have developed a new device, the MEMS flux concentrator, that solves these problems. Often flux concentrators (soft magnetic materials) are placed around magnetic sensor to increase the field. In the new device, the flux concentrators are placed on MEMS flaps that are driven to oscillate in the plane of the sensor, by electrostatic comb drives, at a frequency of about 15 kHz. The two MEMS flaps are connected by Si springs so that there is an 180$^{\circ}$ out of phase normal mode. If the amplitude of the motion is 12 microns, the amplitude of the magnetic field at the position of the sensor varies by a factor of about two. At 15 kHz, the sensor is operating in a region where the 1/f noise is often reduced by several orders of magnitude. Spin valves were employed as the magnetic sensor. SOI wafers were used in the fabrication. Because the Q of the mechanical resonance is 30, only microwatts of power are required to drive the motion. [Preview Abstract] |
Wednesday, March 23, 2005 8:48AM - 9:00AM |
N13.00005: Anti-Stokes solid-state random laser M. Noginov, G. Zhu, C. Small We report on the first demonstration of anti-Stokes solid-state laser operating in the regime, when only one pumping photon is required to excite one electron to the upper laser level. The anti-Stokes stimulated emission, which photon energy was almost fifty percent larger than the energy of the pumping photon, was realized in GaAs \textit{random laser}. Stimulated emission in random lasers is supported by feedback provided by scattering. In the experiment, highly scattering GaAs powder was pumped with $\sim $5 ns pulses of optical parametric oscillator tunable between 920 and 1300 nm. The random laser emission with the maximum at $\approx $885 nm (which corresponds to the edge of the absorption band in GaAs) has been observed when the pumping energy exceeded some critical threshold level. In some measurements, two distinctively different slopes have been found in the input-output curve. At 1100 nm pumping, the stimulated emission threshold scaled with the diameter of the excited spot d as $\sim $d$^{x}$, with x$\le $2. This behavior is typical to one-photon pumping of anti-Stokes GaAs random laser, while at two-photon pumping, the expected range of x is 3$<$x$<$4. The longest pumping wavelength, at which the stimulated emission in GaAs random laser has been obtained, was equal to 1300 nm. This implies that in an ideal medium without loss the cooling effect per photon can be as high as 46{\%}. [Preview Abstract] |
Wednesday, March 23, 2005 9:00AM - 9:12AM |
N13.00006: Suppression of spatial hole-burning in a standing wave solid-state laser with a degenerate resonator Po-Tse Tai, Hsiao-Hua Wu, Wen-Feng Hsieh We numerically and experimentally demonstrated that the spatial hole burning in a solid-state laser with a standing wave resonator can be suppressed in use of a tightly-focused pumping beam. The laser can self- adjust its mode waist to match the small pump volume when it is operated in a degenerate cavity configuration, so that variation of the gain profile along the laser crystal can be minimized via the gain saturation. [Preview Abstract] |
Wednesday, March 23, 2005 9:12AM - 9:24AM |
N13.00007: Recovering semiconductor lasers from coherence collapse by orthogonal-polarization optical feedback Tsu-Chiang Yen, Da-Long Cheng A coherent optical feedback (COF) greater than around -30 dB will generally conduct a single-mode semiconductor laser to the coherence collapse that present a multimode oscillation and high-level intensity noise in the laser's output. This research employed orthogonal-polarization optical feedback (OPF) to recover semiconductor lasers from coherence collapse, induced by strong COF, to the solitary single-mode state. Experimentally, under a COF as strong as -14 dB, an OPF of -29 dB could recover the laser's primitive single-mode state from multimode. Moreover, a pre-fed OPF of around -25 dB provided the semiconductor laser with a resistivity against up to -19 dB COF. These results will significantly improve the performance of semiconductor lasers in many applications and provide a new method to investigate the coherence collapse. [Preview Abstract] |
Wednesday, March 23, 2005 9:24AM - 9:36AM |
N13.00008: Nuclear Magnetization by Rotating Magnetic Fields Detected with a Superconducting Quantum Interference Device SeungKyun Lee, Erwin L. Hahn, John Clarke We demonstrate that, in the absence of any static magnetic field, protons in a liquid sample can be polarized along the $z$-direction by application of a magnetic field rotating in the $xy$-plane. By detecting spin precession in 3 $\mu$T with a low-$T_{\mathrm{c}}$ Superconducting QUantum Interference Device, we observed that a rotating field can induce nuclear polarization comparable to that from a static field of the same magnitude. The spin-lattice relaxation times of Cr-doped methanol samples in the frame rotating at 10 kHz were the same as those in the laboratory frame within the error of the experiment. This experiment provides a direct test of the modified Bloch equation that includes spin relaxation in the instantaneous field when strong oscillating fields are present. A field rotating at several kHz is capable of polarizing only materials with short correlation times of spin fluctuation ($\tau_c \ll$ 1 ms) such as liquid. Therefore, use of such fields to prepolarize the sample enables high-resolution liquid-state nuclear magnetic resonance experiments even in the presence of strongly magnetic solid material near the sample. Supported by USDOE. [Preview Abstract] |
Wednesday, March 23, 2005 9:36AM - 9:48AM |
N13.00009: Magnetic resonance elastography detected with a SQUID in microtesla magnetic fields Nathan Kelso, Michael M\"{o}{\ss}le, Whittier Myers, John Clarke, Kristie Koski, Jeffrey Reimer We have used a SQUID-based microtesla magnetic resonance imaging (MRI) system to perform magnetic resonance elastography (MRE) experiments in a measurement field of 132 microtesla. Magnetic resonance elastography is based on MRI and measures three-dimensional displacement and strain fields in a sample. With appropriate data processing this allows for a quantitative map of the physical response of a material to an applied deformation. In the past, MRE experiments using conventional (1.5 tesla and above) MRI systems have demonstrated that MRE may be used as a non-invasive method for measuring stiffness of human tissues, which may aid in the detection and diagnosis of breast cancer and other cancers. Our MRE experiment consists of applying a small axial deformation to a cylindrical sample of 0.5\% agarose gel. For samples approximately 30 mm in height, we were able to measure displacements on the order of 500 micrometers. Supported by USDOE. [Preview Abstract] |
Wednesday, March 23, 2005 9:48AM - 10:00AM |
N13.00010: Correcting Concomitant Gradient Distortion in Microtesla Magnetic Resonance Imaging Whittier Myers, Michael M\"{o}{\ss}le, Nathan Kelso, Alexander Pines, John Clarke Progress in ultra-low field magnetic resonance imaging (MRI) using an untuned gradiometer coupled to a Superconducting Quantum Interference Device (SQUID) has resulted in three-dimensional images with an in-plane resolution of 2 mm. Protons in samples up to 80 mm in size were prepolarized in a 100 mT field, manipulated by $\sim $100 $\mu $T/m gradients for image encoding, and detected by the SQUID in the $\sim $65 $\mu $T precession field. Maxwell's equations prohibit a unidirectional magnetic field gradient. While the additional concomitant gradients can be neglected in high-field MRI, they distort high-resolution images of large samples taken in microtesla precession fields. We propose two methods to mitigate such distortion: raising the precession field during image encoding, and software post-processing. Both approaches are demonstrated using computer simulations and MRI images. Simulations show that the combination of these techniques can correct the concomitant gradient distortion present in a 4-mm resolution image of an object the size of a human brain with a precession field of 50 $\mu $T. Supported by USDOE. [Preview Abstract] |
Wednesday, March 23, 2005 10:00AM - 10:12AM |
N13.00011: Mixing with the radiofrequency single-electron transistor Loren Swenson, Daniel Schmidt, Sequoyah Aldridge, David Wood, Andrew Cleland By configuring a radio-frequency single-electron transistor as a mixer, we have demonstrated good charge sensitivity and large bandwidth around a tunable center frequency. Our implementation greatly increases the spectral range achievable for sensitive broadband charge measurements with this device, limited only by the RC time of the transistor's center island. In the current demonstration operating at 300 mK, a 16 MHz resonance bandwidth has been shown to be tunable to 1.2 GHz with an unoptimized charge sensitivity of $5 \times 10^{-3} e$/Hz$^{1/2}$. [Preview Abstract] |
Wednesday, March 23, 2005 10:12AM - 10:24AM |
N13.00012: Quantum Steering of Electron Wave in 70nm InAs Y-Branch Switches G. M. Jones, C. H. Yang, M. J. Yang, Y. B. Lyanda-Geller We report quantum steering of electron wavefunction in gated Y-branch switches (YBS). In this quantum regime, the coherent transport characteristics are drastically different from their classical counterparts. The practical difficulty in realizing YBS has been in fabricating nanometer-scale electron waveguides without depleting electrons in narrow channels. We overcome this hurdle by using InAs because it has zero lateral depletion width. We first fabricated cross-junctions for bend resistance measurements to verify the relatively long elastic mean free path of our devices. In addition, in order to verify the gating effect, we characterized quantum point contact devices made on the same wafer and observed a series of quantum conductance plateaus. Finally, we measured conductances through two drains of YBS, and observed oscillatory transconductances that are always out of phase. Our observation not only verifies the quantum steering of electron wave functions in a semiconductor waveguide, but it also opens up possibilities for further studies of quantum switches in multiple-terminal, nanometer-scale structure for information processing. [Preview Abstract] |
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