| 1. |
- Andersen, Torben, et al.
(author)
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Novel concept for large deformable mirrors
- 2006
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In: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286. ; 45:7
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Journal article (peer-reviewed)abstract
- Large, high-bandwidth deformable mirrors (DMs) with thousands of actuators for adaptive optics are of high interest for existing large telescopes and indispensable for construction of efficient future extremely large telescopes. Different actuation and sensing principles are possible. We propose a novel concept using commercially available voice coil actuators attached to the back of the mirror with suction cups and using LVDT sensors on the actuators for local stabilization. Also, a new low-cost sensor for easy measurement of DM displacement or velocity has been developed. It has a sensitivity better than 20 nm and a bandwidth wider than 20 to 1000 Hz. Finally, studies are in progress of global, hierarchical mirror form controllers based on many parallel multiple-input, multiple-output regulators of low order.
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| 2. |
- Andersson, Åke, et al.
(author)
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Coherent synchrotron radiation in the far infrared from a 1-mm electron bunch
- 2000
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In: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286. ; 39:12, s. 3099-3105
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Journal article (peer-reviewed)abstract
- The coherent generation of synchrotron radiation by an electron storage ring is predicted for wavelengths equal to or longer than the electron bunch length. With typical bunch lengths of approximately 1 cm, diffraction and chamber-screening effects have so far blocked observation of coherent radiation from a conventional radiation beamline. In the low-energy, second-generation light source MAX-I, the magnet lattice has been tuned to a small momentum compaction factor, allowing rms bunch lengths as short as 1 mm. Here we report the coherent far-infrared emission observed from such a bunch. The paper discusses the origin of coherent synchrotron radiation for Gaussian and non-Gaussian electron bunches, and the procedure used to generate such bunches. The emission was characterized using the infrared beamline at MAX-I, including an interferometer, a liquid-helium-cooled bolometer detector, waveguide high-pass filters, and a conductive-grid polarization filter. The intensity of the coherent radiation is greater by a factor of 2×103 to 6×103 than normal incoherent synchrotron radiation, and is seen between 8 and 22 cm-1.
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| 3. |
- Benckert, Lars, et al.
(author)
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Measuring true in-plane displacements of a surface by stereoscopic white-light speckle photography
- 1987
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In: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 26:2, s. 167-169
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Journal article (peer-reviewed)abstract
- When in-plane surface deformations are measured using white-light speckle photography, errors arise if an out-of-plane displacement is present. Stereoscopic photography resolves this problem and makes possible the measurement of true in-plane displacements. A rigid-body translation is introduced to determine unambiguously the direction of the displacement
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| 4. |
- Bengtsson, Tomas, 1983, et al.
(author)
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Optical flow estimation on image sequences with differently exposed frames
- 2015
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In: Optical Engineering. - 1560-2303 .- 0091-3286. ; 54:9, s. Article Number: 093103-
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Journal article (peer-reviewed)abstract
- Optical flow (OF) methods are used to estimate dense motion information between consecutive frames in image sequences. In addition to the specific OF estimation method itself, the quality of the input image sequence is of crucial importance to the quality of the resulting flow estimates. For instance, lack of texture in image frames caused by saturation of the camera sensor during exposure can significantly deteriorate the performance. An approach to avoid this negative effect is to use different camera settings when capturing the individual frames. We provide a framework for OF estimation on such sequences that contain differently exposed frames. Information from multiple frames are combined into a total cost functional such that the lack of an active data term for saturated image areas is avoided. Experimental results demonstrate that using alternate camera settings to capture the full dynamic range of an underlying scene can clearly improve the quality of flow estimates. When saturation of image data is significant, the proposed methods show superior performance in terms of lower endpoint errors of the flow vectors compared to a set of baseline methods. Furthermore, we provide some qualitative examples of how and when our method should be used.
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| 5. |
- Bengtsson, Tomas, 1983, et al.
(author)
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Super-resolution reconstruction of high dynamic range images in a perceptually uniform domain
- 2013
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In: Optical Engineering. - 1560-2303 .- 0091-3286. ; 52:10
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Journal article (peer-reviewed)abstract
- Super resolution is a signal processing method that utilizesinformation from multiple degraded images of the same scene in order to reconstruct an image with enhanced spatial resolution. The method is typically employed on similarly exposed pixel valued images, but it can be extended to differently exposed images with a high combined dynamicrange. We propose a novel formulation of the joint super-resolution, high dynamic range image reconstruction problem, using an image domain in which the residual function of the inverse problem relates to the perception of the human visual system. Simulated results are presented,including a comparison with a conventional method, demonstrating that the proposed approach avoids some severe reconstruction artifacts.
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| 6. |
- Bergström, Per, et al.
(author)
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Shape verification using dual-wavelength holographic interferometry
- 2011
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In: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 50:10
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Journal article (peer-reviewed)abstract
- In automotive industry there is an interest of controlling the shape of a large number of identical components on-line in the manufacturing process. We propose a method to do this by capturing a digital hologram of the object and then using information from its computer aided design (CAD) model to calculate the shape and determine the agreement between the manufactured object and the CAD-model. The holographic recording of the object is done using dual wavelengths with a synthetic wavelength of approximately 400 μm. The optical measurement results in a wrapped phase map with the phase values in the interval [−π, π]. Each phase interval represents a depth distance on the object of about 0.2 mm. The phase unwrapping is done iteratively using information from the CADmodel. This implies that it is possible to measure large discontinuities on the surface of the measured object. The method also gives a point-to-point correspondence between the measurement and the CAD-model which is vital for tolerance control.
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| 7. |
- Bergström, Per, 1981-, et al.
(author)
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Virtual projective shape matching in targetless CAD-based close-range photogrammetry for efficient estimation of specific deviations
- 2018
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In: Optical Engineering. - : SPIE - International Society for Optical Engineering. - 0091-3286 .- 1560-2303. ; 57:5
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Journal article (peer-reviewed)abstract
- A concept for targetless, computer-aided design (CAD)-based, close-range photogrammetry for online shape inspection is introduced. The shape of an object, which is arbitrarily located on a conveyor belt, is to be measured and compared with its nominal shape as defined by a CAD model. For most manufactured objects, deviations are only measured at a few given comparison points. These deviations can be estimated using local photogrammetry based on a priori geometrical information given by the CAD model and the comparison points. Our method results in faster output with higher precision, because we do not generate a shape representation of the entire measured object using typical photogrammetric methods. Images depicting the object from convergent angles are captured by an array of cameras in a precalibrated network, and the CAD model is matched and aligned, within the projective geometry of the camera network, to the depicted object in the images without the use of targets. An algorithm for solving this virtual projective targetless shape matching problem is presented.
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| 8. |
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| 9. |
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| 10. |
- Brunnström, K, et al.
(author)
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Object Detection in Cluttered Infrared Images.
- 2003
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In: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 42:2, s. 388-399
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Journal article (peer-reviewed)abstract
- Implementation of the Johnson criteria for infrared images is the probabilities of a discrimination technique. The inputs to the model are the size of the target, the range to it, and the temperature difference against the background. The temperature difference is calculated without taking the background structure into consideration, but it may have a strong influence on the visibility of the target. We investigated whether a perceptually based temperature difference should be used as input. Four different models are discussed: 1. a probability of discrimination model largely based on the Johnson criteria for infrared images, 2. a peak signal-to-noise ratio model, 3. a signal-to-clutter ratio model, and 4. two versions of an image discrimination model based on how human vision analyzes spatial information. The models differ as to how much they try to simulate human perception. To test the models, a psychophysical experiment was carried out with ten test persons, measuring contrast threshold detection in five different infrared backgrounds using a method based on a two-alternative forced-choice methodology. Predictions of thresholds in contrast energy were calculated for the different models and compared to the empirical values. Thresholds depend on the background, and these can be predicted well by the image discrimination models, and better than the other models. Future extensions are discussed.
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