PHYSICS DISSERTATION DEFENSE: Jordan O'Neal

Date
Fri September 16th 2022, 12:00 - 1:00pm
Location
PAB 102/103

When built, the MAGIS-100 atom interferometer will be the largest in the world. But it's still missing a key component: a detailed camera. Stanford University

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Ph.D. Candidate:  Jordan O'Neal

Research Advisor: 
Philip Bucksbaum

Date: September 16, 2022
Time: 12:00 pm

Location: PAB 102/103


Zoom Link: 
https://stanford.zoom.us/j/98203820889

Zoom Password: email nickswan [at] stanford.edu for password.

 

Title: 
Tracking Charge Migration with Attosecond X-ray Pulses from a Free-Electron Laser


Abstract: 
Photochemistry begins with electrons reacting to an incident field on an attosecond timescale.  At longer time scales, the electron dynamics couples to the nuclear dynamics, driving chemical changes.  I report an observation of the purely electronic attosecond response, dubbed charge migration, in the time domain, and find the coherence lifetime is at least a few femtoseconds.  We use attosecond X-ray pump/attosecond X-ray probe pulses developed recently by our group at the Linac Coherent Light Source~(LCLS) X-ray free-electron laser in an impulsive ionization scheme.  The short pulse enables high temporal resolution, while the X-ray wavelength allows measurements of the charge density around specific atomic sites.  This measurement agrees with simulations including the effect of zero-point geometry spread, showing how the nuclear wavepacket affects charge migration.

From a separate experiment, I report an observation of impulsive stimulated X-ray Raman scattering~(SXRS) using a single attosecond X-ray pulse.  Impulsive SXRS is a building block for nonlinear X-ray spectroscopic techniques that can pump and probe charge migration of valence electrons in a controllable manner.  I will also discuss planned future experiments to implement impulsive SXRS in a Raman interferometry scheme to measure and manipulate charge migration more systematically.