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Physics & Astronomy Colloquium
Thursdays, 3:30 p.m.
Call us at: (323) 343-2100
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Fall Quarter 2012 Schedule

Biological Sciences Building, BIOS 335
Refreshments - 3:15 p.m., Colloquium - 3:30 p.m


Andrew Jayich
California Institute of Technology

"Optomechanics with SiN Membranes:
Laser Cooling Starting with a 400 mK Base Temperature "

Abstract: Optomechanics is a diverse field where harmonic oscillators are coupled to an optical field via the radiation pressure force. The mechanical devices range from atom clouds to the kilogram scale mirrors used in the LIGO observatories. There are promising applications and there is exciting fundamental physics research taking place. The starting point for many interesting measurements begins with the mechanical device in its ground state, where it has less than a phonon worth of energy. I will present on an optomechanical system from the Jack Harris Lab at Yale University where a high finesse cavity is coupled to a millimeter scale SiN membrane that is anchored to a He3 fridge at 400 mK. We have laser cooled to an occupancy of 100 phonons. The cooling is limited by mechanical vibrations that will hopefully be eliminated in the newest design allowing us to reach the ground state.


Benjamin Zuckerman
University of California, Los Angeles

"Violent Events in Rocky Planetary Systems:
Implications for the Fate of Technological Civilizations, Including our Own"

Abstract: We and Earth will take a voyage of 10 billion years from its violent formation 4.6 billion years ago to its possible violent demise 4-5 billion years from now.  Along the way we will consider a few tumultuous eras suffered by Earth's biosphere, including the present, human-dominated, era. Such eras, from origins to final resting places, can be explored by drawing upon recent astronomical studies of other planetary systems.  We speculate on what the co-evolution of stars and planetary systems portends for the long-term fate of our technological civilization and the prevalence, or lack thereof, of other technological civilizations.


Hu (Tiger) Cao
Department of Physics and Astronomy,
University of California, Riverside

"Phase Transformations in Highly Electrostrictive (1-x)Pb(Mg 1/3 Nb 2/3 O 3 )-xPbTiO 3 and Magnetostrictive (Fe-xGa) Crystals"

Abstract: X-ray and Neutron scattering were performed on two “smart” materials: highly electrostrictive (1-x)Pb(Mg 1/3 Nb 2/3 )-xPbTiO 3 (PMN-xPT) ( ferroelectric) and highly magnetostrictive Fe-xGa alloys (ferromagnetic) . Our studies have revealed that the structural inhomogeneity on a nanoscale is the structural origin of ultrahigh performance observed in these two materials. In PMN-xPT, various intermediate monoclinic (M) phases have been found, which structurally ‘bridge' the rhombohedral (R) and tetragonal (T) ones across the morphtropic phase boundary (MPB). It was found that the phase stability of PMN-xPT crystals is quite fragile: depending not only on modest changes in E (= 0.5kV/cm), but also on the direction along which E is applied. An alternative interpretation for the phase fragility is the “ferroelectric adaptive phase” model, which theorized that the monoclinic phases are miniaturized T or R nanotwins (~10nm) determined by elastic lattice accommodation. In Fe-xGa alloys, h igh resolution transmission electron microscopy showed a DO 3 (bcc) nano-dispersion within an A2 (bcc) matrix, whereas the diffuse neutron scattering surprisingly established a confined distortion of nano-dispersed DO 3 precipitates with a large strain. Investigations as a function of Ga content showed that the diffuse scattering intensity is the strongest near Fe-0.19Ga where the magnetostriction is also maximal: This confirms that the enhanced magnetostriction is directly related to the structural heterogeneity of DO 3 nano-precipitates.




Yaroslav Tserkovnyak
University of California, Los Angeles

" Magnon Transport, Condensation, and Topology in Insulators "

Abstract: In this talk, I will discuss several new topics in spintronics dealing with electrically insulating magnetic media. While lacking Ohmic dissipation, these systems are promising for a range of interesting collective phenomena, quantum correlations, topological properties, and even useful devices: all in insulating systems driven far out of equilibrium. Specifically, I will discuss our recent ideas on magnetocaloritronic "nanomachines," steady-state Bose-Einstein condensation of magnons, thermal Hall effect, and magnetic dynamics in topological insulator heterostructures.


Doug E. MacLaughlin
University of California, Riverside

" Muons: Exotic Probes of Materials and Molecules"

Abstract: Cross-fertilization of experimental techniques often leads to unexpected advances in science and technology.  An example is MRI, the application of nuclear magnetic resonance (NMR) to medical imaging.  This talk will introduce another such marriage: the muon spin rotation (µSR) technique.  µSR, like NMR and other magnetic resonance techniques, provides a magnetic probe of matter on the atomic scale, but µSR is unusual in that nuclear physics methods provide its basic technology.  Spin-polarized muons are obtained from a "meson factory" accelerator and are implanted in a sample.  The direction of emission of the subsequent decay positron, which is correlated with the muon spin orientation at the time of decay, is monitored using standard techniques of experimental nuclear physics.  The time evolution of this orientation is controlled by the local magnetic field at the muon site.  The muon can be used as a probe of its surroundings, as in NMR, or as an exotic particle in its own right, in a solid or molecular environment.  Contributions of µSR experiments to a number of research areas will be discussed.


Andrea M. Armani
Assistant Professor and Fluor Early Career Chair in Engineering,
Mork Family Dept of Chemical Engineering and Materials Science
University of Southern California

"Non-Linear Behavior in Integrated Optical Devices"

Abstract: As the dimensions of integrated photonic devices have been reduced from the milli to the nano-scale, non-linear optical effects have become more apparent.  One device which is particularly interesting to study is the optical resonator.  Because it is able to confine light for long periods of time, very large circulating optical intensities build up inside the device, and this build-up power scales with device size.  As a result, smaller resonators are more susceptible to non-linear effects.  Many researchers have leveraged this feature to create new and interesting resonator-based devices, such as integrated lasers, while other researchers have focused on eliminating the behavior as it can create instabilities.  This presentation will highlight our current research in both domains.  Specifically, I will discuss our development of a Raman-based laser which operates in both air and buffer; this device has clear applications in the bio-detection arena.  Additionally, I will present our work on hybrid devices or devices which consist of multiple materials.  These hybrid systems offer optical and mechanical properties which are not attainable with conventional material systems, such as athermal performance, and are able to study the fundamental behavior of the different materials.  Additionally, new research exploring bio-hybrid devices for communications will be presented.



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