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In
this talk, I
will discuss
some of the
major results
from my
postdoctoral
work at
JILA/CU
Boulder, as
well as new
projects we
are embarking
on in the
Weichman Lab,
which launched
in July 2020
at Princeton
Chemistry.
Direct
frequency comb
spectroscopy
is a
sensitive,
broadband, and
precision
technique that
can be used to
interrogate
the quantum
structure of
unprecedentedly
large
molecular
species.
Frequency
combs are
light sources
consisting of
thousands of
evenly spaced,
sharp
frequency
“teeth.”
Cavity-enhanced
frequency comb
spectroscopy
(CE-FCS)
matches a
comb’s evenly
spaced
spectral
structure to
the resonant
modes of a
high-finesse
optical
cavity. This
method allows
for
simultaneous
detection of
absorption
signal across
the comb
spectrum,
extremely high
frequency
resolution,
and high
sensitivity as
the cavity
enhances the
interaction
length between
light and
sample. We
combined
cryogenic
buffer gas
cooling of
large
molecules with
CE-FCS in
order to
measure the
rovibrational
structure of
buckminsterfullerene
(C60), a
molecule of
great
fundamental
and
astrochemical
interest and a
longstanding
spectroscopic
challenge. I
will discuss
the details of
these
measurements,
which
represent the
first direct
probe of the
quantum
state-resolved
structure of
C60 and
establish it
as by far the
largest
molecule for
which a
state-resolved
spectrum has
been reported.
For
applications
in
cavity-enhanced
spectroscopy,
optical
cavities
enhance the
strength of
light-matter
interactions
and increase
absorption
sensitivity.
The Weichman
Lab’s future
interests lie
in a more
exotic regime
for
intracavity
molecules. The
interaction of
light and
matter is
typically weak
and can be
treated
perturbatively.
This picture
breaks down in
the regime of
strong
coupling,
where the rate
of
light-matter
interaction
competes with
the
dissipation of
excitations.
In this
regime,
Schrödinger’s
cat-like
superposition
states with
mixed
light-matter
character,
dubbed
polaritons,
emerge.
Polaritons
inherit the
coherent,
wavelike
nature of
light while
maintaining
local
molecular
interactions
and structure.
Polaritonic
molecules may
therefore
demonstrate
distinct
reactivity
from their
ordinary
uncoupled
counterparts,
representing
an extremely
rich sandbox
for new
chemistry. I
will discuss
two new
polariton
chemistry
projects we
are starting
at Princeton.
We are setting
out to build a
detailed
picture of how
molecular
polaritons
behave and
react, using
ultrafast and
precision
spectroscopy
to follow the
reaction
dynamics of
benchmark
condensed-phase
and gas-phase
systems under
strong
light-matter
coupling.
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