Optical tweezers use the forces exerted by a strongly focused beam of light to trap and move objects ranging in size from tens of nanometres to tens of micrometres. Since their introduction in 1986, the optical tweezer has become an important tool for research in the fields of biology, physical chemistry and soft condensed matter physics. Recent advances promise to take optical tweezers out of the laboratory and into the mainstream of manufacturing and diagnostics; they may even become consumer products. The next generation of single-beam optical traps offers revolutionary new opportunities for fundamental and applied research.

http://physics.nyu.edu/grierlab/nreview2c/nreview2c.pdf

A revolution in optical manipulation

Photonic crystal fibers guide light by corralling it within a periodic array of microscopic air holes that run along the entire fiber length Largely through their ability to overcome the limitations of conventional fiber optics—for example, by permitting low-loss guidance of light in a hollow core—these fibers are proving to have a multitude of important technological and scientific applications spanning many disciplines The result has been a renaissance of interest in optical fibers and their uses

https://science.sciencemag.org/content/sci/299/5605/358.full.pdf

Photonic crystal fibers

Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

As they travel through space, some light beams rotate. Such light beams have angular momentum. There are two particularly important ways in which a light beam can rotate: if every polarization vector rotates, the light has spin; if the phase structure rotates, the light has orbital angular momentum (OAM), which can be many times greater than the spin. Only in the past 20 years has it been realized that beams carrying OAM, which have an optical vortex along the axis, can be easily made in the laboratory. These light beams are able to spin microscopic objects, give rise to rotational frequency shifts, create new forms of imaging systems, and behave within nonlinear material to give new insights into quantum optics.

/pdf/orbital-angular-momentum-origins-behavior-and-applications-1sv8qfuhrs.pdf

Orbital angular momentum: origins, behavior and applications

Internet data traffic capacity is rapidly reaching limits imposed by optical fiber nonlinear effects Having almost exhausted available degrees of freedom to orthogonally multiplex data, the possibility is now being explored of using spatial modes of fibers to enhance data capacity We demonstrate the viability of using the orbital angular momentum (OAM) of light to create orthogonal, spatially distinct streams of data-transmitting channels that are multiplexed in a single fiber Over 11 kilometers of a specially designed optical fiber that minimizes mode coupling, we achieved 400-gigabits-per-second data transmission using four angular momentum modes at a single wavelength, and 16 terabits per second using two OAM modes over 10 wavelengths These demonstrations suggest that OAM could provide an additional degree of freedom for data multiplexing in future fiber networks

http://science.sciencemag.org/content/sci/340/6140/1545.full.pdf

Terabit-Scale Orbital Angular Momentum Mode Division Multiplexing in Fibers

The success of optical tweezers in cellular biology 1 is in part due to the wide range of forces that can be applied, from femto- to hundreds of pico-Newtons; nevertheless extending the range of applicable forces to the nanoNewton regime opens access to a new set of phenomena that currently lie beyond optical manipulation. A successful approach to overcome the conventional limits on trapping forces involves the optimization of the trapped probes. Jannasch et al. 2 demonstrated that an anti-reflective shell of nanoporous titanium dioxide ( aTiO 2 , n shell = 1.75) on a core particle made out of titanium dioxide in the anatase phase ( cTiO 2 , n core = 2.3) results in trappable microspheres capable to reach forces above 1 nN. Here we present how the technique can be further improved by coating the high refractive index microspheres with an additional anti-reflective shell made out of silica ( SiO 2 ). This external shell not only improves the trap stability for microspheres of different sizes, but also enables the use of functionalization techniques already established for commercial silica beads in biological experiments. We are also investigating the use of these new microspheres as probes to measure adhesion forces between intercellular adhesion molecule 1 (ICAM-1) and lymphocyte function-associated antigen 1 (LFA-1) in effector T-Cells and will present preliminary results comparing standard and high-index beads.

Improved antireflection coated microspheres for biological applications of optical tweezers

Colloidal Interactions with Optical Fields: Optical Tweezers

We demonstrate phase conjugation by means of degenerate four-wave mixing from a colloidal crystal. The nonlinear medium is provided by a periodic spatial refractive index grating created in a colloidal suspension of dielectric microparticles trapped in the intensity distribution of two nearly copropagating interfering laser beams. Phase conjugation is achieved for a probe beam carrying orbital angular momentum as evidenced by the inversion of the topological charge of a phase singularity within the beam. The e ciency and nonlinear parameters of the colloidal crystal as well as its lattice properties are measured and compared to theoretical predictions and previous experimental work.

Phase conjugation and four-wave mixing in a colloidal medium

We demonstrate the use of holographic optical tweezers for the optical trapping and manipulation of arrays of airborne water droplets (aerosols). Making use of a phase-only spatial light modulator we present evidence of stable, interactive manipulation of both single and multiple aerosol droplets, of the order of 10 microns in diameter, and also their controlled coagulation. We discuss the advantages, disadvantages, and limitations of using a spatial light modulator for droplet manipulation including the implications of the update speed of the device (a Holoeye LC-R2500 SLM), diffraction efficiency, and droplet growth and evaporation due to laser intensity variations. We will examine the generic difficulties of trapping in air, working in the absence of inertial damping. Finally we will discuss the applications of the above work in fields such as atmospheric chemistry and microfluidic microchemical reactors whilst presenting preliminary results on fusion of two or more droplets of differing phases.

Controlled aerosol manipulation using holographic optical tweezers

We present a compact, diffuser assisted, single-pixel computational camera. A rotating ground glass diffuser is adopted, in preference to a commonly used digital micro-mirror device (DMD), to encode a two-dimensional (2D) image into single-pixel signals. We retrieve images with an 8.8% sampling ratio after the calibration of the pseudo-random pattern of the diffuser under light-emitting diode (LED) illumination. Furthermore, we demonstrate hyperspectral imaging with line array detection by adding a diffraction grating. As the random and fixed patterns of a rotating diffuser placed in the image plane can serve as 2D modulation patterns in single-pixel imaging, we do not need further calibration for spectral imaging case since we use a parallel recovery strategy for images at all wavelengths. The implementation results in a cost-effective single-pixel camera for high-dimensional imaging, with potential for imaging in non-visible wavebands.

/pdf/single-pixel-diffuser-camera-4ncuwjl5th.pdf

David McGloin

Papers

Improved antireflection coated microspheres for biological applications of optical tweezers

Colloidal Interactions with Optical Fields: Optical Tweezers

Phase conjugation and four-wave mixing in a colloidal medium

Controlled aerosol manipulation using holographic optical tweezers

Single-Pixel Diffuser Camera