Lateral speckle size in Phase Retrieval systems. - In: DGaO-Proceedings, ISSN 1614-8436, Bd. 113.2012, A34, insges. 2 S.
Phase Retrieval (PR) techniques provide a complimentary approach to Digital Holography (DH) for estimating the complex amplitude of a wavefield. If one uses a Gerchberg-Saxon type iterative approach, generally two intensity distributions at different optical planes are captured. Fast Fourier Transform (FFT) based algorithms are then employed to iteratively recover the phase information. Once we have estimated the complex amplitude of the wavefield we can use numerical propagation algorithms to calculate the distribution at any optical plane. We expect however that the finite size of the camera aperture and the sampling effect introduced by the camera pixels will act to reduce the performance of the optical system. In this manuscript we attempt to examine these performance limiting factors in more detail using a special field as the input into our system; namely a speckle field. This particular type of field contains high spatial frequencies which in turn are related to the lateral speckle size. A series of PR experiments at different capture planes are conducted and we report on how the system performance is effected.
http://www.db-thueringen.de/servlets/DocumentServlet?id=21323
RBF-based optical surfaces. - In: DGaO-Proceedings, ISSN 1614-8436, Bd. 113.2012, P39, insges. 2 S.
Freeform optical surfaces offer additional degrees of freedom for designing imaging systems without rotational symmetry. This allows for a reduction in the number of optical elements, leading to more compact and lightweight systems, while at the same time improving the image quality. This also enables new areas of application. Commonly used representations for freeform surfaces are x-y-polynomials, Zernike polynomials and NURBS. Radial basis functions (RBF) have been used for many years e.g. in artificial neural networks and functional approximation and can also be used to describe optical surfaces. In this contribution we investigate properties specific to RBF-based optical surfaces and compare the performance of RBF-based surfaces to other representations in selected optical imaging systems. Interesting aspects include the dependency on the number of RBF that are summed to form the surface, the locality structure and its effects on optimization.
http://www.db-thueringen.de/servlets/DocumentServlet?id=21333
Ghost images for optical systems with tilted object plane. - In: DGaO-Proceedings, ISSN 1614-8436, Bd. 113.2012, P38, insges. 2 S.
Ghost images are formed by light that is partially reflected by optical surfaces. Ghost images may cause contrast reduction and may veil parts of the nominal image. Performing ghost image analysis during the design stage is important to ensure the success of the system. In a previous paper (Applied Optics, Vol. 50, Issue 15, pp. 2305-2315 (2011), modeling ghost images was performed using a sequential ray tracing technique. Synthesizing ray paths into ghost and nominal paths and performing sequential ray tracing provides a powerful tool for describing ghost image formation in optical systems. We address the applicability of Scheimpflug principle for ghost image formation and we present a new criterion to identify problematic ghost images in the paraxial approximation. Numerical examples are considered and discussed.
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Measuring the refractive index of double-clad fibers using an interferometric technique. - In: DGaO-Proceedings, ISSN 1614-8436, Bd. 113.2012, P32, insges. 2 S.
Multiple-beam Fizeau interferometry is an accurate, simple, and nondestructive technique in the field of fiber research. Inserting the fiber into the liquid silvered wedge causes the fringes to shift across the fiber region with respect to the fringes at the liquid region. Fringe shift is a function in the geometry of the different regions of the fiber and the refractive index profile of the fiber. In a previous paper (Applied Optics, Vol. 50, No. 31, (2011)) the theory for the interference pattern formation was developed. In this contribution, we extend the theory to include graded index double-clad fibers. In addition, we discuss the experimental aspects of the measuring system.
http://www.db-thueringen.de/servlets/DocumentServlet?id=21331
Optimized Alvarez phase plates for hyperspectral imaging. - In: DGaO-Proceedings, ISSN 1614-8436, Bd. 113.2012, B35, insges. 2 S.
In the late 1960s Alvarez and Lohmann independently suggested cubic phase plates as varifocal elements. A variety of different theoretical as well as experimental approaches have been discussed since. Today compact tunable optics is of specific interest e.g. in miniaturized optical systems. Recently developed fabrication technologies like diamond turning or milling nowadays enable the fabrication of higher order freeform surface profiles as implementation of efficient phase plates for an optimization of the imaging properties. We present a non-paraxial analysis of the imaging behavior of diffractive, refractive and hybrid Alvarez-Lohmann lenses with increased numerical aperture. Our analysis includes the influence of lateral focus shifts as well as monochromatic and polychromatic aberrations over the tuning range. Experimental results with phase plates fabricated by diamond milling and lithographic techniques will be presented.
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Design and integration of a multi-channel fluorescence detector. - In: DGaO-Proceedings, ISSN 1614-8436, Bd. 113.2012, P1, insges. 2 S.
In combination with fluidic systems, fluorescence detectors have a large variety of applications e.g. in biomedicine for ph-sensoring or the characterization of chemical reaction processes. Highly integrated and miniaturized optofluidic microsystems enable the handling of very small sample volumes in so-called segmented flow systems, which is beneficial for the practical application. A single-channel fluorescence sensor using planar integrated free space optical systems has been developed in the past. In order to increase the measuring flexibility and accuracy the extension to a multi-wavelength and multi-channel sensor system based on this concept is currently investigated. We present the concept, optical design and fabrication strategy of a highly integrated free space optical fluorescence detector for the application in a segmented-flow environment. The performance of the system is characterized and the application as a biochemical analysis system is discussed.
http://www.db-thueringen.de/servlets/DocumentServlet?id=21328
Realistic ray-tracing of surface and volume diffusers. - In: Proceedings, ISBN 9783941417847, (2012), S. 55-70
Low-cost uncooled infrared detector using microcantilever arrays with optical readout. - In: 23rd Micromechanics and Microsystems Europe Workshop, (2012), insges. 4 S.
We report on characterization of an uncooled infrared (IR) detector set-up which serves as a low-cost IR camera technology platform. The imaging detector consists of a passive microsensor and a simple optical readout. IR radiation is detected by a microcantilever focal plane array (FPA) which working principle is described. The cantilever serves as a thermo-mechanical transducer, converting photon energy in a reservible mechanical deflection on the micro.level. The mechanical deflection is captured by a visual imager (CCD / CMOS) which is part of the simple optical readout and converted into changes of gray scale intensity. Finally, we present first results of real-time thermographic imagery taken by the uncooled IR detector.
Hyperchromatic confocal sensor systems. - In: 8th EOS Topical Meeting on Diffractive Optics, (2012), insges. 2 S.
Free-form optical trapping systems. - In: Optical trapping applications, ISBN 978-1-55752-909-1, (2011), insges. 1 S.
We report a breakthrough in designing and fabricating free-form trapping systems which opens up a new class of systems for optical micromanipulation. We show 3D-trapping with a specialized optics (WD=650 [my]m), which is made of a single piece of PMMA.
http://dx.doi.org/10.1364/OTA.2011.OTTuC2p