Showing papers by "David McGloin published in 2012"
TL;DR: The binary coalescence of aqueous droplets has been observed in a single-beam gradient-force optical trap by measuring the time-dependent intensity for elastic scattering of light from the trapping laser and the time scale for equilibration of a composite droplet to ambient conditions has been determined.
Abstract: The binary coalescence of aqueous droplets has been observed in a single-beam gradient-force optical trap. By measuring the time-dependent intensity for elastic scattering of light from the trapping laser, the dynamics of binary coalescence have been examined and the time scale for equilibration of a composite droplet to ambient conditions has been determined. These data are required for modeling the agglomeration of aqueous droplets in dense sprays and atmospheric aerosol. Elastic-light scattering from optically trapped particles has not been used previously to study the time-resolved dynamics of mixing. It is shown to offer a unique opportunity to characterize the binary coalescence of aqueous droplets with radii from 1 to 6 μm. The study of this size regime, which cannot be achieved by conventional imaging methods, is critical for understanding the interactions of droplets in the environment of dense sprays.
25 citations
TL;DR: In this paper, the authors demonstrate directed jetting from pulsed laser-induced cavities subjected to a burst of focused ultrasound, and interpret their observations in terms of radiation forces exerted on the cavity, due to the pressure gradient introduced to the ultrasound focus by its presence.
Abstract: We demonstrate directed jetting from pulsed laser-induced cavities subjected to a burst of focused ultrasound. Alignment of the ultrasound focus and the pressure amplitudes in the vicinity of the cavity dictate the direction and length of the resulting jet, respectively. We interpret our observations in terms of radiation forces exerted on the cavity, due to the pressure gradient introduced to the ultrasound focus by its presence. We support our hypothesis with a linear analysis of the force distribution across the cavity surface, at the moment of maximum inflation, which shows reasonable predictive agreement with the observed jet characteristics.
22 citations
TL;DR: In this paper, an optimized optical tweezers system based upon the conical refraction of circularly polarized light in abiaxial crystal is presented, which avoids distortions to the Lloyd plane rings.
Abstract: We present an optimized optical tweezers system based upon the conical refraction of circularly polarized light in a
biaxial crystal. The described optical arrangement avoids distortions to the Lloyd plane rings that become apparent when
working with circularly polarized light in conventional optical tweezers. We demonstrate that the intensity distribution of
the conically diffracted light permits optical manipulation of high and low refractive index particles simultaneously.
Such trapping is in three dimensions and not limited to the Lloyd plane rings. By removal of a quarter waveplate the
system also permits the study of linearly polarized conical refraction. We show that particle position in the Raman plane
is determined by beam power, and indicates that true optical tweezing is not taking place in this part of the beam.
15 citations
TL;DR: It is demonstrated that annular beams allow droplets to be trapped at higher powers, and with reduced axial displacement with increasing power, than Gaussian beams, and a reduction in the axial scattering forces is confirmed using this theoretical model.
Abstract: In this paper we explore the trapping of aerosol droplets using an annular beam, formed by blocking the central portion of a Gaussian beam, and quantify the improvements over conventional Gaussian beam traps. Recent work on the modelling of single aerosol dynamics within an optical tweezer trap [Burnham et al., Journal of the Optical Society of America B, 2011, 28, 2856-2864] has indicated that the use of annular beams can allow smaller droplets to be trapped, which we experimentally verify. We also demonstrate that annular beams allow droplets to be trapped at higher powers, and with reduced axial displacement with increasing power, than Gaussian beams. We confirm these results, due to a reduction in the axial scattering forces, using this theoretical model. Finally back focal plane interferometry is used to determine the axial and lateral trap stiffnesses for a series of droplets, showing a significant increase in the axial : lateral trap stiffness ratio from 0.79 ± 0.04 to 1.15 ± 0.04 when an annular beam is used.
13 citations
TL;DR: The use of a low cost games console interface, the Microsoft Kinect for the control of holographic optical tweezers and a study into the effect of using such a system upon the quality of trap generated are presented.
Abstract: The increased application of holographic optical manipulation techniques within the life sciences has sparked the
development of accessible interfaces for control of holographic optical tweezers. Of particular interest are those that
employ familiar, commercially available technologies. Here we present the use of a low cost games console interface, the
Microsoft Kinect for the control of holographic optical tweezers and a study into the effect of using such a system upon
the quality of trap generated.
10 citations
TL;DR: A neat study shows that a sheet of laser light can be used to reflect light- absorption liquid droplets and manipulate their trajectories, which may open up new ways of controlling and studying aerosols.
Abstract: A neat study shows that a sheet of laser light can be used to reflect light-absorbing liquid droplets and manipulate their trajectories. This observation may open up new ways of controlling and studying aerosols.
TL;DR: In this paper, a novel method for spatial mapping of the luminescent properties of single optically trapped semiconductor nanowires by combing dynamic optical tweezers with micro-photoluminescence is presented.
Abstract: We present a novel method for spatial mapping of the luminescent properties of single optically trapped semiconductor
nanowires by combing dynamic optical tweezers with micro-photoluminescence The technique involves the use of a
spatial light modulator (SLM) to control the axial position of the trapping focus relative to the excitation source and
collection optics When a nanowire is held in this arrangement, scanning the axial position of the trapping beam enables
different sections of the nanowire axis to be probed In this context we consider the axial resolution of the luminescence
mapping and optimization of the nanowire trapping by spherical aberration correction