SBU

 

AMP
                                      Physics

 

 

Groups | Seminars || Courses | Outreach

Seminars

Seminars will be held held at room S-141 in the Physics and Astronomy Department building on Mondays at 4:00 PM, unless noted otherwise.

 

Fall 2017






September 11, 2017

Ruaridh Forbes

NRC Ottawa/University College London

Strong-Field Probes of Ultrafast Molecular Dynamics

(Host: Tom Weinacht)

Strong laser-field based methods such as high-harmonic generation and strong-field ionization (SFI) are considered novel probes of ultrafast molecular dynamics. Details of an experimental femtosecond time-resolved SFI study of the excited state dynamics of NO$_{2}$ using channel-resolved above-threshold ionization (CRATI) as the probe technique will be presented. CRATI makes use of PhotoElectron-PhotoIon COincidence (PEPICO) spectroscopy to study correlations in fragmentation dynamics in molecular systems. The use of PEPICO and covariance methods allows us to correlate ATI photoelectrons associated with a particular SFI electron orbital ionization channel. In disentangling the excited state dynamics of NO$_{2}$, the complex roles of one-photon excitation, multiphoton excitation to higher-lying neutral states, non-adiabatic dynamics and several neutral and ionic dissociation channels are examined. The results will likely have implications for all SFI based time-resolved studies in polyatomic molecules.



September 29, 2017 (Fri 2:30pm)

Prof. Doerte Blume
The University of Oklahoma

Probing the helium dimer and trimer with fast, intense lasers

(Host: Dominik Schneble)

Helium is the only element that remains liquid under normal pressure down to zero temperature. Below 2.17K, the bosonic isotope helium-4 undergoes a phase transition to a superfluid. Motivated by this intriguing bulk behavior, the properties of finite-sized helium droplets have been studied extensively over the past 25 years or so. A number of properties of liquid helium-4 droplets are, just as those of nuclei, well described by the liquid drop model. The existence of the extremely fragile helium dimer was proven experimentally in 1994 in diffraction grating experiments. Since then, appreciable effort has gone into creating and characterizing trimers, tetramers and larger clusters. The ground state and excited state of the helium trimer are particularly interesting since these systems are candidates for Efimov states. The existence of Efimov states, which are unique due to scale invariance and an associated limit cycle, was predicted in 1971. However, till recently, Efimov states had -- although their existence had been confirmed experimentally -- not been imaged directly. Recently, ingenious experimental advances that utilize femtosecond lasers made it possible to directly image the static quantum mechanical density distribution of helium dimers and trimers. I will review some of these experiments and related theoretical calculations that led to the experimental detection of the excited helium trimer Efimov state. Extensions to the time domain will also be discussed. Intriguing laser-kick induced dynamics of the fragile helium dimer is observed experimentally and analyzed theoretically. These initial results open the door for future studies that probe scattering length dominated few-body systems using fast, intense lasers.



October 23, 2017

Prof. Jonathan Simon
University of Chicago

An introduction to topological photonics

(Host: Hal Metcalf

Charged particles placed in a magnetic field exhibit unique behaviors resulting from the handedness of the Lorentz force. From chiral dynamics in the non-interacting limit to fractional statistics when the particles are allowed to interact with one another, the quantum Hall effect has introduced topology into physics in unexpected and beautiful ways. In this seminar I'll provide an introduction to the quantum Hall effect of non-interacting and strongly interacting electrons, and then discuss the development of a photonic platform to study analogous physics. In particular, I will describe an exploration of a quantum Hall effect of light using a non-planar optical resonator to create a synthetic magnetic field for photons; from here I will describe innovations that have enabled us to employ Rydberg atoms to mediate interactions between photons, and our plans for combining these two exciting new platforms to the entangled, fractional Hall fluids that result.






October 30, 2017

Prof. Jenny Magnes
Vassar College

Diffraction Time Series of Live C. elegans

(Host: Hal Metcalf)

The locomotion of microorganisms is presently understood through video analysis under a microscope. While effective in many aspects, this method is often time-consuming, computationally heavy and omits subtle components of the motion. Time dependent diffraction signals are a complimentary method that speeds up certain aspects of the data collection and analysis while reducing error. We use C. elegans as a sample species since they are easily maintained and have been the focus of many neuroscience studies.

 

C. elegans are free-living soil-dwelling nematodes that navigate in three dimensions. They move both on a solid matrix like soil or agar in a sinusoidal locomotory pattern called crawling and in liquid in a different pattern called swimming. The roles played by sensory information provided by mechanosensory, chemosensory, and thermosensory cells that govern plastic changes in locomotory patterns and switches in patterns are only beginning to be elucidated. We describe an optical approach to measuring nematode locomotion in three dimensions that does not require a microscope and enables us to begin to explore the complexities of nematode locomotion under different conditions.

 

The experimental method presented in this work allows for the characterization of locomotion and the distinction of phenotypes using Fourier analysis. Even more excitingly, principles of complex and chaotic systems indicate that the locomotion of the wildtype as well as a mutant known as ‘Roller’ is chaotic in nature.





November 6, 2017

Dr. Scott Diddams
NIST

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(Host: Tom Allison)

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November 13, 2017

Dr. Anthony Cirri
Stony Brook University

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(Host: Tom Allison)

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November 17, 2017 (Friday)

Prof. Kunal Das
Kutztown University

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(Host: Tom Bergeman)

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2017