RESUMEN

We show that the generalized phase contrast method (GPC) can be used as a versatile tool for shaping an incident Gaussian illumination into arbitrary lateral beam profiles. For illustration, we use GPC in an energy-efficient phase-only implementation of various apertures that do not block light but instead effectively redirect the available photons from a bell-shaped light distribution. GPC-based generation of lateral beam profiles can thus be achieved using a simplified optical implementation as it eliminates the need for a potentially lossy initial beam shaping. The required binary phase input is simple to fabricate for static applications and can be easily reconfigured up to device frame refresh rates for dynamic applications.

RESUMEN

We explore the dynamic properties of multiple-beam optical traps to manipulate arrays of microstructures for biosensor applications. Multiple optical traps are generated by a virtually loss-less transformation of input phase patterns into high-intensity trapping-beams. A direct image projection of the phase patterns enables an adjustable number of optical traps in addition to instantaneous control of the position, size, shape and intensity of each trapping-beam. We present experimental results showing various colloidal formations through dynamic optical manipulation of polystyrene microspheres and yeast cells in aqueous media. The experimental configurations are geared towards the use of multiple-beam optical traps for biosensor applications.

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RESUMEN

We demonstrate the use of a phase-only liquid-crystal spatial light modulator (SLM) for polarization-controlled rotation and alignment of an array of optically trapped birefringent particles. A collimated beam incident upon a two-dimensional lenslet array yields multiple foci, scaled to produce optical gradient traps with efficient three-dimensional trapping potentials. The state of polarization of each trapping beam is encoded by the SLM, which acts as a matrix of wave plates with computer-controlled phase retardations. Control of the rotation frequency and alignment direction of the particles is achieved by the transfer of tunable photon spin angular momentum.

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RESUMEN

We explain the vulnerability of the phase-only encryption procedure suggested by Seo and Kim [Opt. Lett. 28, 304 (2003)] and clarify issues regarding its robustness and degree of security compared with those of a previously reported phase-only encryption method.