We showed that the optomechanical oscillations exhibit sensitivity to the density
and viscosity of fluid present in the
device, thus demonstrating a noteworthy
Other groups have published impressive results using optomechanical coupling to engineer phenomena previously
known from atomic systems, including
ground-state laser cooling, slow light
and induced transparency. 4-5 Our result
provides a new bridge between the worlds
of fluidics and optomechanics, which
could now open up disruptive applications in quantum-limited biological
and chemical sensing. Furthermore, the
traveling acoustic WGMs we generate
possess angular momentum, which also
creates the possibility of optomechanical
interactions with vortices in superfluids
Optomechanical systems that enable strong phonon-photon coupling have been with us for a while
but have never been demonstrated
with non-solid phases of matter. The
motivation to perform optomechanics
experiments in fluid-phase arises
with interest in superfluids for
ultra-low-loss optomechanics, and
also for optomechanical interrogation
of biological analytes such as living
cells. 1 However, attempts to achieve
optomechanical oscillation with
a device submerged in fluid have
proven challenging, as phonons tend
to escape into a surrounding medium
having high acoustic impedance.
Our team solved this problem by
confining the liquid within the device,
demonstrating an optomechanical
system that operates with fluids. 2, 3 Our
device is based on a silica microcapil-lary resonator through which fluids
can flow with convenient microfluidic
control. This device supports ultra-high-Q optical whispering-gallery
modes (WGMs) that are used to excite
and interrogate a variety of acoustic
resonances including wineglass modes,
breathing modes and acoustic WGMs.
The actuation forces are generated
through optical electrostriction and
also through centrifugal pressure
of light. The diversity of available
mechanical modes enables vibrational
rates spanning 2 MHz – 11,000 MHz
on a single physical device, even with
highly viscous fluids inside. Because
fluids are now confined within the
device, the optical and acoustic losses
by absorption and sound radiation are
small enough to enable optomechanics.
(Left) Temporal interference between pump and scattered light occurs on a photo-detector at the acoustic frequency and is measured electrically. (Top, right) Acoustic
vibrations are generated on the microfluidic resonator via forces exerted by light confined
in ultra-high-Q optical modes. (Bottom, right) A 99 MHz acoustic WGM on a water-filled
resonator that is optically generated by means of electrostriction.
Gaurav Bahl ( firstname.lastname@example.org)
University of Illinois at Urbana
Champaign, Ill., U.S.A.
Kyu Hyun Kim, Wonsuk Lee,
Jing Liu, Matthew Tomes,
Xudong Fan and Tal Carmon
University of Michigan at
Ann Arbor, Mich., U.S.A.
1. L.A. DeLorenzo et al.
2. G. Bahl et al. Nat. Comm.
4, 2994 (2013).
3. K.H. Kim et al. Light Sci. App.
2, e110 (2013).
4. J. Chan et al. Nature 478, 89
5. S. Weis et al. Science 330,
Bridging Two Worlds:
200 400 600 800 1,000
(NIR diode laser)
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