Giant Optical Manipulation

We demonstrate a new principle of optical trapping and manipulation increasing more than 1000 times the manipulation distance by harnessing strong thermal forces while suppressing their stochastic nature with optical vortex beams. Our approach expands optical manipulation of particles into a gas media and provides a full control over trapped particles, including the optical transport and pinpoint positioning of $\sim 100\mu \mathrm{m}$ objects over a meter-scale distance with $\pm 10\mu \mathrm{m}$ accuracy.

Figure 1

Experimental setup of an optical trapping system for long-range transport of aerosol particles. The vortex beam is formed by the diffraction hologram DH; $L1$ and $L2$ are collimators which control the beam parameters, and the propagation direction is controlled by the moving mirror $M$. Particle transport visualization is performed in the longitudinal (microscope MO1) and transverse (microscope MO2) directions; BS—beam splitter; $T$—glass target; NF—notch filter to cut off the laser radiation;WL—white light source; and C—cuvette with particles. The inset shows the intensity distribution inside the vortex-induced pipeline. It varies from low [dark grey (blue)] to high [grey (red)] values. The arrow shows the direction $z$ of the particles’ transport, the latter are represented by (yellow) balls.

Figure 2

Carbon particles used for the giant transport and manipulation. (a) Structure of trapped carbon particles by scanning electron microscopy. (b) Measured time of flight $t$ for four different particles in the 1.5 m-long optical vortex pipeline. The average photophoretic speed $⟨\nu ⟩$ and its variation during transport is $⟨{\nu }^2⟩=8.1\pm 0.4\mathrm{mm}/\mathrm{s}$ for the particle marked (A), $11.7\pm 0.6\mathrm{mm}/\mathrm{s}$ (B), $13.7\pm 0.7\mathrm{mm}/\mathrm{s}$ (C), and $21.8\pm 0.7\mathrm{mm}/\mathrm{s}$ (D). (c) Optical microscope images of particles deposited on the substrate after the measurements in (b).

Figure 3

Hollow glass microspheres used in giant trap experiments. (a)–(c) Scanning electron microscopy images of trapped single microsphere; (b) same sphere broken to measure shell thickness; (c) magnified edge of the broken shell showing the carbon coating layer $\sim 180\mathrm{nm}$ and the glass shell thickness $\sim 400\mathrm{nm}$. (d),(e) The snapshots in longitudinal and transverse cross sections, respectively, of the particle with characteristic size $a=35\mu \mathrm{m}$, moving in the vortex pipeline; the vortex ring radius in (d),(e) is $w=125\mu \mathrm{m}$. (f) Average speed $⟨\nu ⟩$ (markers) of microspheres versus particle radius $a$ in the optical pipeline of length $L=30\mathrm{cm}$, with vortex beam waist $w_0=75\mu \mathrm{m}$ and power $P=0.8\mathrm{W}$. Solid curve: least-squares fit to experimental data, $⟨\nu ⟩={\nu }_0(a/w_0{)}^3$, with ${\nu }_0=14.8\pm 1.3\mathrm{cm}/\mathrm{s}$; for comparison, dashed curves show the same function with parameter ${\nu }_0=27$ and 7 cm/s.

Figure 4

Remote manipulation of particles using the optical vortex pipeline. (a) Principle of operation for targeted delivery of particles. Inset explains the method of stopping the particle before the target $T$ using balance of forces between the main beam [light grey (green) arrows] and the beam reflected from the substrate [grey (red) arrows]. (b) Example of the remote deposition of glass microspheres; the letters “ANU” stands for the Australian National University, and the positioning accuracy is $\pm 10\mu \mathrm{m}$ over the distance of 0.5 m. (c) Transverse stability of static trapping; solid (red) line encircles the area of particle localization; the radius of the sphere $a=50\mu \mathrm{m}$. Dashed (green) line shows the vortex ring (intensity maximum) with radius $w=236\mu \mathrm{m}$; white lines show the transverse displacement of the particle $R=61\mu \mathrm{m}$ from vortex axis due to gravitation.