Ronald Kampmann

Hybrid optical (freeform) components—functionalization of nonplanar optical surfaces by direct picosecond laser ablation

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.

Fast and scalable algorithm for the simulation of multiple Mie scattering in optical systems.

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.

Perturbed Talbot patterns for the measurement of low particle concentrations in fluids

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.

Efficient and precise simulation of multiple Mie scattering events using GPGPUs

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.

Optimized systems for energy efficient optical tweezing

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.

Thermographischer Detektor basierend auf einem neuartigen Mikro-Spiegel Sensor

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.

Iterative design process for highly efficient optical trapping systems

The development of an optical system for trapping particles in air is presented. Based on optics design as well as optical force simulations an efficient optical system is designed, manufactured and characterized.

Three-dimensional laser ablation for functionalization of non-planar optical surfaces

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...

Synthetic design and integrated fabrication of multifunctional hybrid beam shapers

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.