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Optical tweezers use the force from a light beam to implement a precise gripping tool. Based purely on an optical principle, it works without any bodily contact with the object. In this paper we describe an optical tweezers that targets an application within the framework of nuclear magnetic resonance (NMR) spectroscopy of small objects, which are embedded inside a microfluidic channel that will be integrated in a micro-NMR detector. In the project’s final stages, the whole system will be installed within the wide bore of a superconducting magnet. The aim is to precisely maintain the position of the object to be measured, without the use of susceptibility disturbing materials or geometries. In this contribution we focus on the design and construction of the tweezers. For the optical force simulation of the system we used a geometrical optics approach, which we combined with a ray fan description of the output beam of an optical system. By embedding both techniques within an iterative design process, we were able to design efficient optical tweezers that met the numerous constraints. Based on details of the constraints and requirements given by the application, different system concepts were derived and studied. Next, a highly adapted and efficient optical trapping system was designed and manufactured. After the components were characterized using vertical scanning interferometry, the system was assembled to achieve a monolithic optical component. The proper function of the optical tweezers was successfully tested by optical trapping of fused silica particles.

Zusammenfassung Wir berichten über die Entwicklung eines Wärmebildgeräts, das auf einem neuartigen, patentierten Sensor basiert. Der Sensor besteht aus einer Matrix aus Mikro-Spiegeln für deren Betreib keine Energiezufuhr in Form von Strom oder Spannung und darüber hinaus keine Kühlung notwendig ist. Die Mikro-Spiegel verbiegen sich proportional zur aufgenommen Wärmestrahlung (Infrarot-Intensität), vergleichbar mit einem bi-Metall-Thermometer. Die Verbiegung des einzelnen Mikro-Spiegels wird durch Auslenkung eines, an dem Spiegel reflektierten Kaltlichtstrahles von einem konventionellen CCD-Sensor erfasst und in Echtzeit-Wärmebilder umgewandelt. Das System besteht aus optischen Standardkomponenten. Durch Dünnschichttechnologien und CMOS-Kompatibilität des Sensors besitzt diese Innovation klare Kostenvorteile gegenüber aktuellen Infrarotdetektoren.

Cyanobacteria are blue-green bacteria that are abundant in the environment. Cyanobacteria in the oceans are among the world’s most important oxygen producers and carbon dioxide consumers. Synechocystis is a spherical single-celled cyanobacterium that measures about three thousandths of a millimetre across. Because Synechocystis needs sunlight to produce energy, it is important for it to find places where the light is neither too weak nor too strong. Unlike some bacteria, Synechocystis can’t swim, but it can crawl across surfaces. It uses this ability to move to places where the light conditions are better. It was already known that Synechocystis cells move towards a light source that is shone at them from one side, which implies that the cyanobacteria can “see” where the light is. But how can such a tiny cell accurately detect where light is coming from? Schuergers et al. tracked how Synechocystis moved in response to different light conditions, and found that the secret of “vision” in these cyanobacteria is that the cells act as tiny spherical lenses. When a light is shone at the cell, an image of the light source is focused at the opposite edge of the cell. Light-detecting molecules called photoreceptors respond to the focused image of the light source, and this provides the information needed to steer the cell towards the light. Although the details are different, and although a Synechocystis cell is in terms of volume about 500 billion times smaller than a human eyeball, vision in Synechocystis actually works by principles similar to vision in humans. Schuergers et al.’s findings open plenty of further questions, as other types of bacteria may also act as tiny lenses. More also remains to be learnt about how the cyanobacteria process visual information.

In this work we present the design process as well as experimental results of an optical system for trapping particles in air. For positioning applications of micro-sized objects onto a glass wafer we developed a highly efficient optical tweezer. The focus of this paper is the iterative design process where we combine classical optics design software with a ray optics based force simulation tool. Thus we can find the best compromise which matches the optical systems restrictions with stable trapping conditions. Furthermore we analyze the influence of manufacturing related tolerances and errors in the alignment process of the optical elements on the optical forces. We present the design procedure for the necessary optical elements as well as experimental results for the aligned system.

The performance of optical tweezers in the presence of monochromatic aberrations is investigated theoretically and experimentally. For the calculation of optical forces we use a ray-optics-based force simulation, which is embedded in a ray tracing routine. By considering optical path differences caused by monochromatic aberrations, we are able to simulate their effect on the trapping forces. Optical trapping experiments considering the influence of aberrations were performed with an optical tweezers system, specially adapted to trap particles in gaseous surrounding. The conformity of these measurements with the theoretical predictions verifies the correct performance of the optical force simulation routine. Based on the reliable simulation tool, further theoretical studies are performed on how optical aberrations affect the function and performance of optical tweezers.

An innovative optical system for trapping particles in air is presented. We demonstrate an optical system specifically optimized for high precision positioning of objects with a size of several micrometers within a nanopositioning and nanomeasuring machine (NPMM). Based on a specification sheet, an initial system design was calculated and optimized in an iterative design process. By combining optical design software with optical force simulation tools, a highly efficient optical system was developed. Both components of the system, which include a refractive double axicon and a parabolic ring mirror, were fabricated by ultra-precision turning. The characterization of the optical elements and the whole system, especially the force simulations based on caustic measurements, represent an important interim result for the subsequently performed trapping experiments. The caustic of the trapping beam produced by the system was visualized with the help of image processing techniques. Finally, we demonstrated the unique efficiency of the configuration by reproducibly trapping fused silica spheres with a diameter of 10 μm at a distance of 2.05 mm from the final optical surface.

Mie theory describes the scattering of electromagnetic waves on spheroidal particles whose diameter is comparable to the wavelength of the incident radiation. We have implemented a parallel algorithm using graphics adapters to calculate perpendicular and parallel polarized scattered waves, from which other scattering parameters can be derived. This facilitates parallel propagation of monochromatic electromagnetic waves in scattering media. We have shown that a parallelization can reduce computation time rigorously.

Compared to conventional optics like singlet lenses or even microscope objectives advanced optical designs help to develop properties specifically useful for efficient optical tweezers. We present an optical setup providing a customized intensity distribution optimized with respect to large trapping forces. The optical design concept combines a refractive double axicon with a reflective parabolic focusing mirror. The axicon arrangement creates an annular field distribution and thus clears space for additional integrated observation optics in the center of the system. Finally the beam is focused to the desired intensity distribution by a parabolic ring mirror. The compact realization of the system potentially opens new fields of applications for optical tweezers such as in production industries and micro-nano assembly.

Efficient laser beam shaping is one of the keys to achieve maximum process performance and to exploit new application fields for lasers. However, with increasingly more complex beam shaping tasks typically the challenges related to system size, weight and reliability scale up as more and more conventional optical components like spherical lenses, gratings, prisms etc. are involved. To overcome this traditional tradeoff several optical functions can be integrated in a single hybrid [1] [2] (reflective/diffractive, refractive/ diffractive [3]) optical freeform component enabling miniaturized [4] and robust beam shaping solutions. For the fabrication of these complex optical surfaces we use integrated fabrication techniques (section 2), which combine micromachining of continuous reflective freeform surfaces [5] and precise laser ablation of high frequency diffractive structures efficiently [6]. In this article we focus on the generation of high quality diffractive structures in copper using 3-dimensional picosecond laser ablation within a five-axis ultraprecision micromachining center (section 3).Efficient laser beam shaping is one of the keys to achieve maximum process performance and to exploit new application fields for lasers. However, with increasingly more complex beam shaping tasks typically the challenges related to system size, weight and reliability scale up as more and more conventional optical components like spherical lenses, gratings, prisms etc. are involved. To overcome this traditional tradeoff several optical functions can be integrated in a single hybrid [1] [2] (reflective/diffractive, refractive/ diffractive [3]) optical freeform component enabling miniaturized [4] and robust beam shaping solutions. For the fabrication of these complex optical surfaces we use integrated fabrication techniques (section 2), which combine micromachining of continuous reflective freeform surfaces [5] and precise laser ablation of high frequency diffractive structures efficiently [6]. In this article we focus on the generation of high quality diffractive structures in copper using 3-dimensional pic...

We report on the realization and characterization of a novel infrared imaging system. The prototype setup serves as a technological platform for a low-cost uncooled infrared camera. The core component of the infrared imager is a novel-type surface micro-machined sensor consisting of a micro-mirror focal plane array. A micro-mirror represents one pixel and exhibits a linear deflection upon long wave infrared irradiation (7-14 μm). The thermo-mechanical deflection is captured by an optical configuration and real-time, full-frame thermal imagery is generated. The sensor does not require any power for operation and can be micro-fabricated with as little as three lithographic steps using standard CMOS technology.

The Monte Carlo simulation of light propagation in optical systems requires the processing of a large number of photons to achieve a satisfactory statistical accuracy. Based on classical Mie scattering, we experimentally show that the independence of photons propagating through a turbid medium imposes a postulate for a concurrent and scalable programming paradigm of general purpose graphics processing units. This ensures that, without rewriting code, increasingly complex optical systems can be simulated if more processors are available in the future.

The performance of optical systems is typically improved by adding conventional optical components which is automatically connected to an increasing system size and weight. Hybrid optical freeform components can help to overcome this traditional tradeoff by designing a single complex optical surface that performs several optical functions at once. In this article we present the synthetic design and integrated fabrication of a reflective hybrid beam shaper offering beam deflection, transformation and splitting capabilities. The shape accuracy and surface quality of the component are demonstrated with profilometric measurements. Experimental investigations of the optical performance verify the suitability of the applied fabrication methods and design approach.

The performance of optical systems is typically improved by increasing the number of conventionally fabricated optical components (spheres, aspheres, and gratings). This approach is automatically connected to a system enlargement, as well as potentially higher assembly and maintenance costs. Hybrid optical freeform components can help to overcome this trade-off. They merge several optical functions within fewer but more complex optical surfaces, e.g., elements comprising shallow refractive/reflective and high-frequency diffractive structures. However, providing the flexibility and precision essential for their realization is one of the major challenges in the field of optical component fabrication. In this article we present tailored integrated machining techniques suitable for rapid prototyping as well as the fabrication of molding tools for low-cost mass replication of hybrid optical freeform components. To produce the different feature sizes with optical surface quality, we successively combine mechanical machining modes (ultraprecision micromilling and fly cutting) with precisely aligned direct picosecond laser ablation in an integrated fabrication approach. The fabrication accuracy and surface quality achieved by our integrated fabrication approach are demonstrated with profilometric measurements and experimental investigations of the optical performance.

Behind periodic amplitude or phase objects, the object transmittance is repeated at the so-called Talbot distances. In these planes perpendicular to the propagation direction, Talbot self-images are formed. In the case of plane wave illumination, the distances between the self-images are equally spaced. A periodic pattern called optical carpet or Talbot carpet is formed along the propagation direction. We show theoretically how the presence of spherical particles (10 to 100 μm in diameter) behind gratings of 20 and 50 μm period affects the formation of Talbot carpets and Talbot self-images at 633 nm illumination wavelength. The scattering of the particles is modeled by the Fresnel diffraction of its geometrical shadow. We analytically calculate the interference of the diffraction orders of rectangular and sinusoidal amplitude gratings disturbed by the presence of particles. To verify our model, we present measurements of Talbot carpets perturbed with both opaque disks and transparent spheres, and discuss the effects for various size parameters. We present an approach to simulate the movement of particles within the Talbot pattern in real time. We simulate and measure axial and lateral particle movements within a probe volume and evaluate the effect on the signal formation in a Talbot interferometric setup. We evaluate the best system parameters in terms of grating period and particle-detector-distance for a prospective measuring setup to determine characteristics of flowing suspensions, such as particle volume concentration or particle size distribution.