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

Oriented cell intercalations and cell shape changes are key determinants of large-scale epithelial cell sheet deformations occurring during gastrulation in many organisms. In several cases directional intercalation and cell shape changes have been shown to be associated with a planar cell polarity in the organisation of the actin-myosin cytoskeleton of epithelial cells. This polarised cytoskeletal organisation has been postulated to reflect the directional tension necessary to drive and orient directional cell intercalations. We have now further characterised and applied a recently introduced non-destructive optical manipulation technique to measure the tension in individual cell junctions in the epiblast of chick embryos in the early stages of primitive streak formation. We have measured junctional tension as a function of position and orientation. Junctional tension of mesendoderm cells, the tissue that drives the formation of the streak, is higher than tension of junctions of cells in other parts of the epiblast. Furthermore, in the mesendoderm junctional tension is higher in the direction of intercalation. The data are fitted best with a Maxwell model and we find that both junctional tension and relaxation time are dependent on myosin activity.

https://biorxiv.org/content/biorxiv/early/2018/12/19/501775.full-text.pdf

Measurement of junctional tension in epithelial cells at the onset of primitive streak formation in the chick embryo via non-destructive optical manipulation

We demonstrate that a range of liquid channels can be created within ice blocks using light. We show that channels with dimensions as small as 40  µm can be made using a 1064 nm laser beam coupled through single-mode fibre. This is in contrast to larger 'tapered' fibres that can be made using multimode fibre and more irregular channels using free space beams. The channels can be stabilized over timescales of minutes using powers as low as 30 mW. Furthermore we demonstrate that liquid samples containing particles may be inserted into the channels and present evidence that particles can be trapped and manipulated using a combination of optical and thermal forces within the light-created microchannels. Furthermore we suggest that such techniques could be used to create templates for conventional microfluidic channels.

Optically written optofluidic ice channels

Ghost imaging can capture 2D images with a point detector instead of an array sensor. It therefore offers a solution to the challenge of building area format sensors in wavebands where such sensors are difficult and expensive to produce and opens up new imaging modalities due to high-performance single-pixel detectors. Traditionally, ghost imaging retrieves the image of an object offline, by correlating measured light intensities and applied illuminating patterns. Here we present a feedback-based approach for online updating of the imaging result that can bypass post-processing, termed self-evolving ghost imaging (SEGI). We introduce a genetic algorithm to optimize the illumination patterns in real-time to match the objects shape according to the measured total light intensity. We theoretically and experimentally demonstrate this concept for static and dynamic imaging. This method opens new perspectives for real-time ghost imaging in applications such as remote sensing (e.g. machine vision, LiDAR systems in autonomous vehicles) and biological imaging.

Self-evolving ghost imaging

Droplet microfluidics is an emerging area in miniaturisation of chemical and biological assays, or "lab-on-a-chip"
devices. Normally consisting of droplets flowing in rigid microfluidic channels they offer many advantages over
conventional microfluidic design but lack any form of active control over the droplets. We present work, using
holographic beam shaping, that allows the real time reconfigurability of microfluidic channels allowing us to redirect,
slow, stop, and merge droplets with diameters of approximately 200 microns. A single beam is be sufficient to perform
simple tasks on the droplets but by using holographic beam shaping we can produce multiple foci or continuous patterns
of light that enable a far more versatile tool.

Holographic control of droplet microfluidics

Migratory environments of various eukaryotic cells, such as amoeba, leukocytes and cancer cells, typically involve spatial confinement. Numerous studies have recently emerged, aimed to develop expe...

https://www.tandfonline.com/doi/pdf/10.1080/19420889.2021.1872917

David McGloin

Papers

Measurement of junctional tension in epithelial cells at the onset of primitive streak formation in the chick embryo via non-destructive optical manipulation

Optically written optofluidic ice channels

Self-evolving ghost imaging

Holographic control of droplet microfluidics

Effects of spatial confinement on migratory properties of Dictyostelium discoideum cells.