Single-acquisition wide-field superresolution for telescopes.

A simple optical setup is introduced here that is capable of improving the diffraction-limited angular resolution of a telescope at minimal cost to image quality. The system consists of, at minimum, an axicon and a convex lens located in the optical path of the telescope, which can increase the angular resolution by up to 38%. Analytical results for this resolution gain along with the Strehl ratio of this system are presented along with experimental results, which show a 30% improvement in single-acquisition image resolution with a Strehl ratio of 0.07, agreeing well with predicted values. With an ultrashallow axicon, large increases in Strehl ratio are possible, up to and beyond unity making higher angular resolution measurements possible with little cost to image quality or experimental complexity.

Optoelectric patterning: Effect of electrode material and thickness on laser-induced AC electrothermal flow.

Rapid electrokinetic patterning (REP) is an emerging optoelectric technique that takes advantage of laser-induced AC electrothermal flow and particle-electrode interactions to trap and translate particles. The electrothermal flow in REP is driven by the temperature rise induced by the laser absorption in the thin electrode layer. In previous REP applications 350-700 nm indium tin oxide (ITO) layers have been used as electrodes. In this study, we show that ITO is an inefficient electrode choice as more than 92% of the irradiated laser on the ITO electrodes is transmitted without absorption. Using theoretical, computational, and experimental approaches, we demonstrate that for a given laser power the temperature rise is controlled by both the electrode material and its thickness. A 25-nm thick Ti electrode creates an electrothermal flow of the same speed as a 700-nm thick ITO electrode while requiring only 14% of the laser power used by ITO. These results represent an important step in the design of low-cost portable REP systems by lowering the material cost and power consumption of the system.

On-chip dilution in nanoliter droplets.

Droplet microfluidics is enabling reactions at nano- and picoliter scale, resulting in faster and cheaper biological and chemical analyses. However, varying concentrations of samples on a drop-to-drop basis is still a challenging task in droplet microfluidics, primarily limited due to lack of control over individual droplets. In this paper, we report an on-chip microfluidic droplet dilution strategy using three-valve peristaltic pumps.

Mapping surface tension induced menisci with application to tensiometry and refractometry.

In this work, we discuss an optical method for measuring surface tension induced menisci. The principle of measurement is based upon the change in the background pattern produced by the curvature of the meniscus acting as a lens. We measure the meniscus profile over an inclined glass plate and utilize the measured meniscus for estimation of surface tension and refractive index.

Optoelectrical microfluidics as a promising tool in biology.

Noncontact robotic particle grippers with trapping, manipulation, and release functions are highly desired in cell biology and microfluidics. Optoelectric techniques combine optical and electrokinetic effects to create thousands of such individually addressable traps. By projecting reconfigurable light patterns, these techniques can concentrate molecules, as well as manipulate, sort, and electroporate cells in a programmable manner. We describe the underlying physical mechanisms and discuss applications in biology and future prospects of these devices.

Single-image far-field subdiffraction limit imaging with axicon.

This Letter presents a technique for subdiffraction limit imaging termed Bessel beam microscopy (BBM). By placing a lens in series with an axicon in the optical path of a microscope, the diffraction-limited resolution of the base microscope is improved by one third. This improvement is demonstrated experimentally by resolving individual subdiffraction limit fluorescent beads in a close-pack arrangement. The behavior of the BBM system is explored using angular diffraction simulations, demonstrating the possibility of resolving features spaced as little as 110 nm apart when viewed with a 100×1.4 NA objective. Unique among super-resolution techniques, BBM acquires subdiffraction limit information in a single image with broadband unstructured illumination using only static geometric optics placed between the microscope and camera.

Three-dimensional locating of paraxial point source with axicon.

This Letter presents a theoretical and experimental study of an axicon illuminated by an off-axis paraxial point source. The Fresnel diffraction integral is applied to show that a paraxial point source produces a Bessel beam. A simple analytical relationship is demonstrated between the location of the point source and the spatial frequency and the center of the resulting Bessel beam in the image plane of a camera. Finally, experimental verification is given by translating a point source of light along the optical axis of an axicon and comparing the resulting predicted and recorded beam intensity profiles. The resulting images are then analyzed to predict the location of the point source with excellent accuracy.