Jesper Glückstad

Helico-conical optical beams: a product of helical and conical phase fronts

Helico-conical optical beams, different from higher-order Bessel beams, are generated with a parallel-aligned nematic liquid crystal spatial light modulator (SLM) by multiplying helical and conical phase functions leading to a nonseparable radial and azimuthal phase dependence. The intensity distributions of the focused beams are explored in two- and threedimensions. In contrast to the ring shape formed by a focused optical vortex, a helico-conical beam produces a spiral intensity distribution at the focal plane. Simple scaling relationships are found between observed spiral geometry and initial phase distributions. Observations near the focal plane further reveal a cork-screw intensity distribution around the propagation axis. These light distributions, and variations upon them, may find use for optical trapping and manipulation of mesoscopic particles.

Vision-guided manipulation of colloidal structures

We propose the use of a vision-guided system for the formation and dynamic manipulation of an assembly of microscopic particles. Microscopic particles having visually recognizable characteristics, i.e. shape and color, are arranged and manipulated using patented and recently demonstrated fully dynamic multiple-beam optical trapping for real-time and simultaneous manipulation and control of arrays of particles. A derived application is the simultaneous manipulation of an assembly of particles at the same time as they are observed and identified with microscopic image processing. We will point to novel experiments based on micro-fluidic and lab-on-a-chip technology, where the aim is to attain all-optical and simultaneous control of aggregated micro-structures that can function as channels, reservoirs, sensors and micro-pumps.

Optically fabricated and controlled microtool as a mobile heat source in microfluidics

Microfluidic systems have gained much interest in the past decade as they tremendously reduce sample volume requirements for investigating different phenomena and for various medical, pharmaceutical and defense applications. Rapid heat transfer and efficient diffusive material transport are among the benefits of miniaturization. These have been achieved so far by tediously designing and fabricating application-specific microfluidic chambers or by employing microdevices that can be difficult to integrate in microfluidic systems. In this work, we present the fabrication and functionalization via two-photon polymerization and physical vapor deposition of microstructures that serve as heat sources in microfluidic devices upon laser illumination. In contrast to other existing methods that rely on photo-thermal effects, our microtools are amenable to optical manipulation and can be actuated in specific locations where heat generation is desired. Heating effects manifest in the presence of a temperature gradient, induced fluid flow and the formation of microbubbles.

Rational design of light-controlled microrobots

Light Robotics is one of the newest progenies of the robotics family, bringing together advances in microfabrication and optical manipulation with intelligent control ideas from robotics and Fourier optics. The development of lightcontrollable microrobots capable of performing specific tasks at the microscale requires the ability to sculpt the two protagonists of the story: the light and the microrobots. Complex light sculpting for optical trapping has been in focus for over three decades, and its importance for controlling microscopic objects is well understood. Designing intricate microrobots for the task is a more recent development facilitated by state-of-the-art microfabrication techniques, and particularly by two-photon polymerization. The full 3D design freedom offered by two-photon polymerization opens the door for imagination, while at the same time bringing the responsibility of rationally designing microrobots tailored to specific tasks. In addition to shape and topology features, the surface chemistry of the microrobots can also help steer them towards specific applications. This paper will discuss strategies for the design and fabrication of light-controllable microrobots as a toolbox for biomedical applications.

Track and trap in 3D

Three-dimensional light structures can be created by modulating the spatial phase and polarization properties of an an expanded laser beam. A particularly promising technique is the Generalized Phase Contrast (GPC) method invented and patented at Risø National Laboratory. Based on the combination of programmable spatial light modulator devices and an advanced graphical user-interface the GPC method enables real-time, interactive and arbitrary control over the dynamics and geometry of synthesized light patterns. Recent experiments have shown that GPC-driven micro-manipulation provides a unique technology platform for fully user-guided assembly of a plurality of particles in a plane, control of particle stacking along the beam axis, manipulation of multiple hollow beads, and the organization of living cells into three-dimensional colloidal structures. Here we present GPC-based optical micromanipulation in a microfluidic system where trapping experiments are computer-automated and thereby capable of running with only limited supervision. The system is able to dynamically detect living yeast cells using a computer-interfaced CCD camera, and respond to this by instantly creating traps at positions of the spotted cells streaming at flow velocities that would be difficult for a human operator to handle.

Three-dimensional intensity distribution of helico-conical optical beams

Helico-conical optical beams are a recently introduced class of beams that multiplicatively combine helical and conical phase fronts. Focusing these beams leads to a spiral intensity distribution at the focal plane of the lens. Further theoretical and experimental examination reveals interesting three-dimensional intensity patterns near the focal region, including a cork-screw structure around the optical axis. Variations on these light distributions based on the superposition of multiple helico-conical beams are also presented here. These beams are expected to yield interesting dynamics when applied to the optical trapping of microscopic particles, such as dielectric microspheres or even biological cells.

Optically driven microtools fabricated by UV lithography and RIE

We demonstrate the use of multiple optical traps for driving various microfabricated silica structures in liquid host medium. Multiple counterpropagating-beam traps are formed using a generalized phase contrast (GPC) -based optical trapping system. A combination of UV-lithography and reactive-ion etching (RIE) is employed to fabricate the microtools whose design includes having multiple appendages with rounded endings by which optical traps hold and actuate them. Experiments show the collective and user-coordinated utility of multiple beams for driving microstructured objects whose future integration may lead to optically controlled micromachineries.

A 3D interactive optical manipulation platform

Three-dimensional light structures can be created by modulating the spatial phase and polarization properties of the laser light. A particularly promising technique is the Generalized Phase Contrast (GPC) method invented and patented at Riso National Laboratory. Based on the combination of programmable spatial light modulator devices and an advanced graphical user-interface the GPC method enables real-time, interactive and arbitrary control over the dynamics and geometry of synthesized light patterns. Recent experiments have shown that GPC-driven micro-manipulation provides a unique technology platform for fully user-guided assembly of a plurality of particles in a plane, control of particle stacking along the beam axis, manipulation of multiple hollow beads, and the organization of living cells into three-dimensional colloidal structures. These demonstrations illustrate that GPC-driven micro-manipulation can be utilized not only for the improved synthesis of functional microstructures but also for non-contact and parallel actuation crucial for sophisticated opto- and micro-fluidic based lab-on-a-chip systems.

Far-field technique for tunable coupling to high-order guided modes of photonic crystal fibers

We investigate the potentials of using a far-field technique for tunable coupling to high-order guided modes of photonic crystal fibers. The field distribution matched for coupling to the fiber is generated by the optical Fourier transform of grating-based phase patterns dynamically encoded on a spatial light modulator. Tuning the parameters of phase-only binary diffractive patterns can modulate both amplitude and phase of the coupling field. Experiments demonstrate tunable and spatially controllable coupling to the second-order mode of a commercially available index-guided micro-structured fiber with a triangular lattice air-hole structure.

Integrated miniaturized laboratories using dynamic multiple-beam optical manipulators

We use fully dynamic multiple-beam optical manipulators to directly control the activity on miniaturized laboratories that can be operated under a microscope. Scaling down conventional laboratory procedures to micron scale devices facilitates localized synthesis/analysis of chemicals and speeds-up biological assays while maintaining accuracy in the results. The switching mechanism in micro-fabricated fluidic channels and the control of pumps, valves, mixers, filters, separators and the like can be controlled using dynamic light handles. Moreover, continuous liquid flows can be used to transport particles throught the micro-channels and integrate a range of microfluidic components into fully functional devices.