Multi-particle three-dimensional coordinate estimation in real-time optical manipulation

oai:ojs.pkp.sfu.ca:article/304We have previously shown how stereoscopic images can be obtained in our three-dimensional optical micromanipulation system [J. S. Dam et al, Opt. Express 16, 7244 (2008)]. Here, we present an extension and application of this principle to automatically gather the three-dimensional coordinates for all trapped particles with high tracking range and high reliability without requiring user calibration. Through deconvolving of the red, green, and blue colour planes to correct for bleeding between colour planes, we show that we can extend the system to also utilize green illumination, in addition to the blue and red. Applying the green colour as on-axis illumination yields redundant information for enhanced error correction, which is used to verify the gathered data, resulting in reliable coordinates as well as producing visually attractive images

An optically actuated surface scanning probe

We demonstrate the use of an extended, optically trapped probe that is capable of imaging surface topography with nanometre precision, whilst applying ultra-low, femto-Newton sized forces. This degree of precision and sensitivity is acquired through three distinct strategies. First, the probe itself is shaped in such a way as to soften the trap along the sensing axis and stiffen it in transverse directions. Next, these characteristics are enhanced by selectively position clamping independent motions of the probe. Finally, force clamping is used to refine the surface contact response. Detailed analyses are presented for each of these mechanisms. To test our sensor, we scan it laterally over a calibration sample consisting of a series of graduated steps, and demonstrate a height resolution of ∼ 11 nm. Using equipartition theory, we estimate that an average force of only ∼ 140 fN is exerted on the sample during the scan, making this technique ideal for the investigation of delicate biological samples

Dynamic optical manipulation of colloidal systems using a spatial light modulator

A method and mathematical foundation are presented for generating multiple-beam optical tweezers capable of introducing complex trapping beam configurations that enable optical manipulation for a variety of colloidal structures. The method is based on the generalized phase contrast technique for generating high intensity beam patterns from an input phase modulation encoded on a spatial light modulator. The mathematical foundation describes issues concerning how the method provides high photon efficiency adequate for generating large array traps while maintaining dynamic features. Experimental results show multiple trapping of up to 25 particles using a 200 mW laser diode operating at 830 nm. Arbitrary array beam configurations are also shown where the shape, position and size can easily be reconfigured and applied for dynamic manipulation of colloidal particles

Orbital angular momentum of photons, atoms, and electrons

The orbital angular momentum of light, and also of waves beyond the electromagnetic spectrum, is a powerful concept in all systems with cylindrical or rotational symmetry. Expressing quantum images in terms of orbital angular momentum modes allows one to describe image rotations in terms of OAM dependent phase shifts. We discuss image rotations, and in particular Faraday rotations in optical systems, and predict a Faraday rotation for electron vortices. Our considerations highlight connections between orbital angular momentum features in different systems, in particular between image rotations in optical and electron systems, and also between parametric processes in parametric down-conversion and atomic cascades. We compare the phasematching conditions of the two latter systems and demonstrate the efficient transfer of OAM modes and their superpositions from near-infrared pump light to blue light in a four-wave mixing process in rubidium vapour