Applications In Optical Manipulation Research Articles

Scattering of an axicon-generated Bessel beam by a sphere

The scattering of an axicon-generated Bessel beam (AGBB) by a sphere is investigated. An analytical formula for the calculation of Beam Shape Coefficients (BSCs) of an AGBB is first derived according to the Integral Localized Approximation (ILA). After the verification of BSCs by the comparison of the reconstructed field using BSCs with the original field obtained from the definition, the far-field scattered intensity is evaluated, and the rainbow produced by AGBB is also studied. The effect of angle α0 on the far-field scattered intensity and the first rainbow is analyzed in detail. Such investigation could provide a useful tool for the research on radiation forces and torques, which is important in optical tweezers and the related optical manipulation applications.

Generation of enhanced evanescent Bessel beam using band-edge resonance

A method for generating enhanced evanescent Bessel beam is reported. When a radially polarized beam is strongly focused onto the last interface of one-dimensional photonic band gap structure, enhanced evanescent J0 type Bessel beam can be generated via the band-edge resonance. Similarly, enhanced evanescent J1 type Bessel beam can be created by reversing the multilayer structure under azimuthally polarized illumination. These enhanced evanescent Bessel fields may have important applications in optical manipulations of nanoparticles.

Generation of electron beams carrying orbital angular momentum

All forms of waves can contain phase singularities. In the case of optical waves, a light beam with a phase singularity carries orbital angular momentum, and such beams have found a range of applications in optical manipulation, quantum information and astronomy. Here we report the generation of an electron beam with a phase singularity propagating in free space, which we achieve by passing a plane electron wave through a spiral phase plate constructed naturally from a stack of graphite thin films. The interference pattern between the final beam and a plane electron wave in a transmission electron microscope shows the 'Y'-like defect pattern characteristic of a beam carrying a phase singularity with a topological charge equal to one. This fundamentally new electron degree of freedom could find application in a number of research areas, as is the case for polarized electron beams.

Controllable rotation of optical beams with bored helical phases

We achieve controllable noninterferometric rotation of a bored helical beam by introducing a phase shift exclusively to the annular helical region of the phase. We present a derivation based on the decomposition of the beams, which shows that a constant phase shift of DeltaPhi between the bore and the surrounding helical phase with topological charge l will rotate the intensity profile by -DeltaPhi/l about its center. The effect of the phase shifting is verified with experiments. This technique is simple, while it preserves the transverse intensity profiles of the beams. Our report may find applications in optical manipulation and trapping.

Three-dimensional photonic "molecules" from sequentially attached polymer-blend microparticles.

We report the observation of 3D linear or branched chains of polymer-blend microspheres generated from liquid droplets of solution where the modified surface structure of the polymer composite results in highly robust interparticle bonds. Using a linear quadrupole to precisely position particles in space, we are able to take advantage of this novel material property to actively assemble particles in programmable three-dimensional architectures. The robust interlocking nature of interparticle linkage gives rise to strongly coupled morphology-dependent resonances in bisphere and trisphere systems, suggesting the possibility of three-dimensional photonic "molecules" and microscale optical manipulation applications.

Optical Manipulation. Biological Applications of Optical Manipulation.

Micromanipulation of biological materials by laser trapping and laser scalpel has now become indispensable for biological studies under observation by high-resolution microscope. Piconewton-scale controlled forces given by infrared laser trapping enable us not only to analyze mechanical rigidity of filamentous macromolecules to support cellular structure but also to measure working forces to promote motor protein molecules. In contrast to such invasive infrared laser trapping, weak focused laser beam of ultraviolet or visible radiation transects biological materials or structures instantaneously and thus can serve as a micro-surgical scalpel for in-situ characterization of living cells. This article reviews recent progress in biological studies applied by these laser techniques, and also discusses the effect of laser irradiation to biological samples.