Drake Cannan

Nonparaxial Mathieu and Weber accelerating beams.

We demonstrate both theoretically and experimentally nonparaxial Mathieu and Weber accelerating beams, generalizing the concept of previously found accelerating beams. We show that such beams bend into large angles along circular, elliptical, or parabolic trajectories but still retain nondiffracting and self-healing capabilities. The circular nonparaxial accelerating beams can be considered as a special case of the Mathieu accelerating beams, while an Airy beam is only a special case of the Weber beams at the paraxial limit. Not only do generalized nonparaxial accelerating beams open up many possibilities of beam engineering for applications, but the fundamental concept developed here can be applied to other linear wave systems in nature, ranging from electromagnetic and elastic waves to matter waves.

Generation of linear and nonlinear nonparaxial accelerating beams

We study linear and nonlinear self-accelerating beams propagating along circular trajectories beyond the paraxial approximation. Such nonparaxial accelerating beams are exact solutions of the Helmholtz equation, preserving their shapes during propagation even under nonlinearity. We generate experimentally and observe directly these large-angle bending beams in colloidal suspensions of polystyrene nanoparticles.

Observation of trapping and transporting air- borne absorbing particles with a single optical beam

We demonstrate optical trapping and manipulation of micron-sized absorbing air-borne particles with a single focused Gaussian beam. Transportation of trapped nonspherical particles from one beam to another is realized, and the underlying mechanism for the trapping is discussed by considering the combined action of several forces. By employing a specially-designed optical bottle beam, we observe stable trapping and optical transportation of light-absorbing particles from one container to another that is less susceptible to ambient perturbation.

Trapping and rotating microparticles and bacteria with moiré-based optical propelling beams

We propose and demonstrate trapping and rotation of microparticles and biological samples with a moiré-based rotating optical tweezers. We show that polystyrene beads, as well as Escherichia coli cells, can be rotated with ease, while the speed and direction of rotation are fully controllable by a computer, obviating mechanical movement or phase-sensitive interference. Furthermore, we demonstrate experimentally the generation of white-light propelling beams and arrays, and discuss the possibility of optical tweezing and particle micro-manipulation based on incoherent white-light rotating patterns.

Mathieu and Weber accelerating beams beyond the paraxial limit

We demonstrate nonparaxial Mathieu and Weber accelerating beams, generalizing the concept of previously found accelerating beams. Such beams bend into large angles along elliptical or parabolic trajectories but still retain nondiffracting and self-healing capabilities.

Rotating Beads and Bacteria with Moiré-Based Optical Tweezers

Since Ashkin’s pioneering work, optical trapping and manipulation have been of great interest to the optical community. Researchers have proposed many techniques for optically rotating trapped particles, but most relied on either mechanical instruments or phase-sensitive interference, which is susceptible to ambient perturbations. Recently, we demonstrated an approach for generating rotating intensity blades using the moire technique. Our propeller-like beams can be generated with variable speed and direction of rotation without requiring mechanical movement or optical interference. Furthermore, they can achieve dynamic control of trapped microparticles and bacteria.