Showing papers by "David McGloin published in 2008"
TL;DR: The single gradient force trapping of water aerosols in the 2-14 micron diameter range using both 532 nm and 1064 nm light, as well as the holographic optical trapping of arrays of aerosols, are discussed.
Abstract: In the following paper, we discuss new methods to trap and manipulate airborne liquid aerosol droplets. We discuss the single gradient force trapping of water aerosols in the 2–14 micron diameter range using both 532 nm and 1064 nm light, as well as the holographic optical trapping of arrays of aerosols. Using this holographic technique, we are able to show controlled aerosol coagulation. We also discuss two techniques based on the radiation pressure trapping of aerosols, namely the dual beam fibre trap and the controlled guiding of aerosols using Bessel beams. We conclude with a discussion of new topics for study based upon these techniques and some possible applications.
95 citations
TL;DR: In this article, holographically generated optical patterns offer greater flexibility for the thermocapillary control of water droplets than Gaussian spots; droplets can be stopped in faster flows while using less optical intensity when the surface tension variations are created by line patterns instead of single spots.
Abstract: We demonstrate that holographically generated optical patterns offer greater flexibility for the thermocapillary control of water droplets than Gaussian spots; droplets can be stopped in faster flows while using less optical intensity when the surface tension variations are created by line patterns instead of single spots. Further, experiments are performed making use of variable light patterns to achieve controlled droplet routing in a four-way cross microfluidic channel. Finally, multiple droplet storage is demonstrated as well as changing drop order.
93 citations
TL;DR: The technique is used to make comparisons between aerosol and colloid tweezing through power spectra analysis of the particle's positions fluctuations for identical particles trapped in a water or air suspending medium.
Abstract: We demonstrate a method for the optical trapping of solid aerosol particles. Suspension of silica particles in ethanol allows their delivery to the trapping volume using a commercial medical nebulizer. The ethanol quickly evaporates, leaving the solid particles trapped in air. We use the technique to make comparisons between aerosol and colloid tweezing through power spectra analysis of the particle’s positions fluctuations for identical particles trapped in a water or air suspending medium.
67 citations
TL;DR: It is shown that fiber based trapping offers a good candidate for studying optical binding in air and is able to hold suspended particles for extended periods of time and to precisely manipulate them over distances of several hundred microns.
Abstract: We present the use of optical fibers to form a counter-propagating optical trap as a means of manipulating both solid and liquid aerosols. We explore the use of single and multimode fibers to achieve trapping of various particles in air, present the trapping properties of the different fiber types and compare the observed trends to those predicted by theory. Using fibers, we are able to hold suspended particles for extended periods of time and to precisely manipulate them over distances of several hundred microns. We discuss the difficulties and advantages of each fiber configuration and conclude with a demonstration that fiber based trapping offers a good candidate for studying optical binding in air.
35 citations
TL;DR: This work reports on the optical trapping of water droplets with a supercontinuum laser source that covers several resonances of the first excited Mie coefficients in contrast to monochromatic trapping.
Abstract: We report on the optical trapping of water droplets with a supercontinuum laser source. Droplet size is determined by observing the spectrum of the on-axis backscattered light. In contrast to to monochromatic trapping, the broad spectrum of the supercontinuum covers several resonances of the first excited Mie coefficients. A minimum value of Q ~0.16 for the trapping efficiency is estimated.
29 citations
TL;DR: A simple and efficient model is presented, which accounts for the diffraction of the strongly localized optical field of the tightly focused laser beam, the spherical aberration introduced by the dielectric glass-to-water interface, and employs the multidipole approximation for force calculations, and is able to reproduce the experimentally measured force map.
Abstract: This paper describes the quantitative force mapping of micron-sized particles held in an optical vortex trap. We present a simple and efficient model, which accounts for the diffraction of the strongly localized optical field of the tightly focused laser beam, the spherical aberration introduced by the dielectric glass-to-water interface, employs the multidipole approximation for force calculations, and is able to reproduce, with quantitative agreement, the experimentally measured force map.
25 citations
TL;DR: The progressive migration of phase singularities is assessed and the predicted increase in fractional orbital angular momentum content of the beam is explained in terms of this gradual process.
Abstract: The vortex emergence process as an integer order Bessel field progresses continuously onto the contiguous higher order Bessel field is studied in detail. We assess the progressive migration of phase singularities and explain the predicted increase in fractional orbital angular momentum content of the beam in terms of this gradual process.
21 citations
28 Aug 2008
TL;DR: In this paper, a real-time reconfigurable beam shaping method was proposed to enable real time reconfigurability of microfluidic channels allowing them to redirect, slow, stop, and merge droplets with diameters of approximately 200 microns.
Abstract: 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.
5 citations
28 Aug 2008
TL;DR: Aerosol tweezing with a supercontinuum laser source has been successfully demonstrated in this article, where saltwater droplets in the range between 3 and 7 microns in diameters are trapped with a 300nm-wide super-continuum spectrum.
Abstract: Aerosol tweezing with a super-continuum laser source has been successfully demonstrated. Salt-water droplets in the range between 3 and 7 microns in diameters are trapped with a 300nm-wide super-continuum spectrum. As the spectrum covers a few Mie resonances, the optical force is averaged and the trapping efficiency varies smoothly with the square of the radius as in the case of the ray optics approximation. On-axis elastically backscattered spectrum allows a direct and precise determination of the trapped droplet. Evaporation of a single droplet is precisely followed using this method. Alternative spectroscopic droplet sizing techniques are proposed and discussed.
1 citations
TL;DR: In this paper, a phase-shifting interferometric method was used to determine the topological charge of multiple singularities embedded in the transverse phase of singular beams, which can be used to identify closely spaced singular points and elucidate the dynamics of optical vortices.
Abstract: We make use of a spatial light modulator to implement a phase-shifting interferometric method to determine the
topological charge of multiple singularities embedded in the transverse phase of singular beams. This method
allows us to discern between closely spaced singular points and elucidate the dynamics of optical vortices as their
charge is increased continually. The transverse phase of beams with a determined phase profile are analyzed
used this technique, yielding the precise location of multiple singularities as well as the value of their topological
charge. We use apply this method to accurately map the phase and study the transit of vortices across fractional
Bessel beams during their continuous order upconversion.
29 Aug 2008
TL;DR: In this article, the authors describe the behavior of optically trapped airborne particles, both solid and liquid, using back focal plane interferometry and measure characteristic power spectra describing the position fluctuations within the trap, and show it is easy to transfer between an over and under damped regime by either varying the trapping power or the distance into the medium the beam is focused.
Abstract: We present results describing the behavior of optically trapped airborne particles, both solid and liquid. Using back focal plane interferometry we measure characteristic power spectra describing the position fluctuations within the trap. We show it is easy to transfer between an over and under damped regime by either varying the trapping power or the distance into the medium the beam is focused. The results assist in the understanding of airborne tweezers and it is hoped having under damped systems could lead to exploring analogies in many areas of fundamental physics.
TL;DR: In this article, the interaction of aerosols with an optical potential, examining the Brownian and optical forces, was explored, and it was shown that optical tweezers can be used for studies of airborne particles.
Abstract: In order to use optical tweezers for studies of airborne particles we must understand the underlying physics. We explore the interaction of aerosols with an optical potential, examining the Brownian and optical forces.
TL;DR: In this paper, the ability of optical tweezers to both trap and probe airbrone particles was discussed and it was shown that both liquid and solid aerosols can be trapped and that even broadband laser sources such as a supercontinuum may be used to trap particles and can probe properties such as evaporation.
Abstract: In this article we discuss the ability of optical tweezers to both trap and probe airbrone particles. We highlight that a number of optical trapping techniques such as holographic optical tweezers and dual beam traps are possible and may open up new ways to analyse aerosols, for atmospheric studies. We show that both liquid and solid aerosols can be trapped and that even broadband laser sources such as a supercontinuum may be used to trap particles and can probe properties such as evaporation.