Unless otherwise noted, all physics seminars and colloquia are held on Tuesdays from 4:45 to 6:00 pm, in Lecture Room 3 of Merrill Science Center. Tea and snacks will be served before seminars at 4:15 in 204 Merrill. If you would like to be mailed seminar announcements, please send an email to Physics.
Contact colloquium organizer Larry Hunter with any questions about colloquia.
Tue, Jan 24, 2017
"Generating and Controlling Ultrafast Electron Pulses for Time-resolved Electron Diffraction"
Ultrafast electron diffraction (UED) is a powerful technique that lets us measure the positions of atoms in a crystal as they evolve during chemical and physical transformations. These measurements can give insight into how materials work on a microscopic level as well as guide the design of devices that respond on fast timescales. For some time, the best-available time resolution in UED has hovered around 100 fs (1 fs =10^-15 s), just shy of the 10 fs resolution required to see the fastest atomic motions. In my talk, I’ll explain how ultrafast electron diffraction works and why it’s challenging to break the 100-fs resolution barrier. I’ll show experimental results on a new technique that uses terahertz electromagnetic fields to compress electron pulses in time. This technique has the potential to improve the resolution of UED below 100 fs and maybe even below ~1 fs, into the regime of electronic dynamics. The talk will also introduce ultrafast electron sources based on laser-triggered electron emission from nanometrically sharp metal tips. Not only is the physics of ultrafast electron emission in this system very rich, but the extraordinarily small source size in comparison with typical ultrafast flat photocathode sources can dramatically improve the beam quality, leading to smaller probe sizes, higher quality diffraction patterns, and enabling new techniques like ultrafast electron holography.
Tue, Jan 31, 2017
Tue, Feb 7, 2017
Tue, Feb 14, 2017
Tue, Feb 21, 2017
Tue, Feb 28, 2017
Tue, Mar 7, 2017
Tue, Mar 21, 2017
"Planet Formation through Radio Eyes."
The disks of gas and dust around young stars provide the raw material and initial conditions for planet formation. Millimeter-wavelength interferometry is a powerful tool for studying gas and dust in planet-forming regions, and it has recently undergone an immense leap in sophistication with the advent of the ALMA interferometer. I will discuss some ways in which millimeter-wavelength interferometry is being used to study the process of planet formation in circumstellar disks, with particular emphasis on the degree to which debris disk structure reflects the dynamics of embedded planetary systems.