Optical Pipeline: Trapping and
Guiding of Airborne Particles
Vladlen G. Shvedov, Andrei V. Rode, Yana Izdebskaya, Anton S. Desyatnikov,
Wieslaw Krolikowski and Yuri S. Kivshar
Optical manipulation of particles with lasers is an indispensable tool
in many branches of science, from physics to biology and medicine. 1 Optical
tweezers, which apply radiation pressure
on transparent particles in liquids, are
leading tools in this field. However, the
e;cient trapping of light-absorbing aerosol particles, such as air contaminants
and novel nanostructured materials, represents a challenge because of dominating thermal or radiometric forces. 2
When an incident light heats a surface
of absorbing particle nonuniformly, gas
molecules rebound o; the surface with
di;erent velocities, thus creating an integrated photophoretic force. For positive
photophoresis, the absorbing particles are
repelled from an intensity maximum, and
stable trapping with Gaussian laser beams
becomes impossible. Recently, we used
two optical vortex beams3, 4 and created
a new type of a stable trap for controlling
absorbing particles in open air. ;e trap
is formed between the focal planes of
counterpropagating vortex beams. Optical vortices create a ring-shaped transverse
intensity distribution, and the particles
are trapped at the intensity minima. Consequently, the heating of trapped particles
is minimal, which is important for in situ
studies of particle properties.
To illustrate photophoretic manipulation of aerosols, we used clusters of
carbon nanoparticles produced by a
high-repetition-rate laser ablation with
typical sizes between 0.1 and 10 µm as
well as hollow glass spheres coated with a
carbon layer to increase light absorption,
with a typical size from 10 to 150 µm.
By retaining only a single vortex beam,
the trap can be converted into an optical
pipeline5 for transporting particles over
large distances in gases. We demonstrated
the transport over 1. 5 m, which is 1,000
times larger than any spatial scale of typical trapping schemes. Moreover, by tilting
(d) Input beam
(a) Light scattered from trapped particle is visible in the center. (Inset) Glass microsphere
suspended in the vortex beam. (b) Photophoretic trapping with two counterpropagating
vortex beams; the imbalance of powers causes the particle to move to the right (left) if the
left (right) beam becomes stronger; for equal powers, the particle sits in the center between
focal planes. (c) Light intensity distribution in the vortex pipeline. (d) Delivery system based
on the vortex pipeline. The position of the vortex beam can be varied by tilting the mirror.
(e) Image shows multiple trapping of some 1,000 carbon particles in a speckle beam.
the vortex beam, the trapped particles
could be delivered to the desired remote
spatial location with accuracy better than
10 µm over a half-meter distance—which
is like shooting a dime from 500 m. Further, using spatially modulated beams, we
could trap many particles simultaneously.
Our approach can be applied for
touch-free transport of containers
holding gases, ultrapure or dangerous
substances, viruses or living cells. ;e
dual-beam optical pipeline, in particular,
allows such movement in opposite directions, acceleration up to several centimeters per second, or holding containers
anywhere in the pipeline. ;e method
is well suited to many light-absorbing
materials and ambient gases or liquids,
and thus can be applied, in particular, in
studies of various airborne particles. t
;is work is supported by the National Health
and Medical Research Council of Australia.
Authors thank J. Mohr for help with the figure.
Wieslaw Krolikowski ( firstname.lastname@example.org)
and coauthors are with the Laser Physics Center
and Nonlinear Physics Center, Research School
of Physics and Engineering, Australian National
University, Canberra, Australia.
to view the video that accompanies
1. K. Dholakia et al. Chem. Soc. Rev. 37, 42-55 (2008).
2. D. McGloin et al. Faraday Discuss. 137, 335-50 (2008).
3. V. G. Shvedov et al. Opt. Express 17, 5743 (2009); V. G.
Shvedov et al., Appl. Phys. A 100, 327-31 (2010).
4. V.G. Shvedov et al. Opt. Express 18, 3137-42 (2010).
5. V.G. Shvedov et al. Phys. Rev. Lett. 105, 118103 (2010).