Affiliation:
1. Purdue University
2. Lawrence Berkeley National Laboratory
3. University of Mary Washington
Abstract
In an ultrafast nonlinear optical interaction, the electric field of
the emitted nonlinear signal provides direct access to the induced
nonlinear transient polarization or transient currents and thus
carries signatures of ultrafast dynamics in a medium. Measurement of
the electric field of such signals offers sensitive observables to
track ultrafast electron dynamics in various systems. In this work, we
resolve the real-time phase of the electric field of a femtosecond
third-order nonlinear optical signal in the molecular frame. The
electric field emitted from impulsively pre-aligned gas-phase
molecules at room temperature, in a degenerate four-wave mixing
scheme, is measured using a spectral interferometry technique. The
nonlinear signal is measured around a rotational revival to extract
its molecular-frame angle dependence from pump-probe time-delay scans.
By comparing these measurements for two linear molecules, carbon
dioxide and nitrogen, we show that the measured second-order phase
parameter (temporal chirp) of the signal is sensitive to the valence
electronic symmetry of the molecules, whereas the amplitude of the
signal does not show such sensitivity. We compare measurements to
theoretical calculations of the chirp observable in the molecular
frame. This work is an important step towards using electric field
measurements in nonlinear optical spectroscopy to study ultrafast
dynamics of electronically excited molecules in the molecular
frame.
Funder
National Science Foundation
U.S. Department of Energy
Cited by
1 articles.
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