| 1. |
- Andersen, Torben, et al.
(författare)
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Novel concept for large deformable mirrors
- 2006
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286. ; 45:7
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Coherent synchrotron radiation in the far infrared from a 1-mm electron bunch
- 2000
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286. ; 39:12, s. 3099-3105
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Measuring true in-plane displacements of a surface by stereoscopic white-light speckle photography
- 1987
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 26:2, s. 167-169
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Optical flow estimation on image sequences with differently exposed frames
- 2015
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Ingår i: Optical Engineering. - 1560-2303 .- 0091-3286. ; 54:9, s. Article Number: 093103-
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Super-resolution reconstruction of high dynamic range images in a perceptually uniform domain
- 2013
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Ingår i: Optical Engineering. - 1560-2303 .- 0091-3286. ; 52:10
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Shape verification using dual-wavelength holographic interferometry
- 2011
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 50:10
-
Tidskriftsartikel (refereegranskat)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.
(författare)
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Virtual projective shape matching in targetless CAD-based close-range photogrammetry for efficient estimation of specific deviations
- 2018
-
Ingår i: Optical Engineering. - : SPIE - International Society for Optical Engineering. - 0091-3286 .- 1560-2303. ; 57:5
-
Tidskriftsartikel (refereegranskat)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.
(författare)
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Object Detection in Cluttered Infrared Images.
- 2003
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 42:2, s. 388-399
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Tidskriftsartikel (refereegranskat)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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| 11. |
- Carlsson, C., et al.
(författare)
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High-frequency analog modulation of oxide confined 670-nm vertical-cavity surface-emitting lasers
- 2004
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 43:12, s. 3138-3141
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the bandwidth limitations and the analog modulation characteristics at microwave frequencies (0.1 to 10 GHz)of a low-capacitance oxide-confined 670-nm InGaAIP vertical-cavity surface-emitting laser (VCSEL). A maximum modulation bandwidth of 6.3 GHz, limited by thermal effects, is achieved. From measurements of distortion and noise, a spurious free dynamic range (SFDR) of 100 dB Hz(2/3) is obtained at frequencies up to 2 GHz, rendering such VCSELs useful for transmission of analog signals. At higher frequencies, the SFDR drops due to the thermally limited resonance frequency.
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| 12. |
- Carlsson, Torgny E., et al.
(författare)
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System for acquisition of three-dimensional shape and movement using digital Light-in-Flight holography
- 2001
-
Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 40:1, s. 67-75
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Tidskriftsartikel (refereegranskat)abstract
- In the development of new products there are two parallel lines for the development process to follow: the traditional or "real" and the new computer aided or "virtual." The traditional line is to develop prototypes that can be used for testing strength, functionality, and visual appearance of the product. In the virtual line digital (CAD) models are developed that can be tested entirely in a computer by simulations, e.g., using finite element analysis (FEA) and other tools. For transformation from the real to the virtual world some kind of 3-D acquisition system is needed. The shape of the model should be measured together with further data concerning the visual appearance, material properties, etc. We develop electronic recording techniques for doing this based on the Light-in-Flight technique. This technology has all the advantages of holography, i.e., apart from the shape it is also possible to measure how much light is reflected from different parts of the object along with interferometric information, which can give mechanical data for the object. This can be used, for example, for visualization and to give tactile and haptic information to a virtual reality system about how the object would be perceived by a person touching it.
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| 13. |
- Carlsson, Torgny, et al.
(författare)
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Practical system for time-resolved holographic interferometry
- 1991
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 30:7, s. 1017-1022
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Tidskriftsartikel (refereegranskat)abstract
- An easily implemented and easily manageable system for time-resolved holographic interferometry is presented. The system consists of a multiple-pulsed Q-switched ruby laser and a rotating disk having radial slits with a constant angular separation. The disk is used to scan the reference beam along a holographic plate, thereby achieving spatial multiplexing. Since the influence on the beam is negligible and a single slit is illuminated by every laser pulse, there is no need for synchronization. The interferometric pattern is achieved by removing the disk and exposing a reference image on the holographic plate. The system may serve as an excellent tool for full-field dynamic measurements. A simple experiment has beem performed showing a sequence of momentary interference patterns on a vibrating plate.
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| 14. |
- Dong, Hui, et al.
(författare)
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Measurement of polarization mode dispersion vectors in optical fibers using a virtual Mueller matrix method
- 2007
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 46:3, s. 035007-
-
Tidskriftsartikel (refereegranskat)abstract
- A virtual Mueller matrix method is proposed to measure the first- and second-order polarization mode dispersion (PMD) vectors in optical fibers. This method not only can use a large frequency step to attain low-noise PMD vector data, but also does not require knowledge of the input polarization states. Our measurement method has a simpler setup and is more accurate than the traditional Mueller matrix method.
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| 15. |
- Eriksson, Fredrik, et al.
(författare)
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Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition
- 2002
-
Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 41:11, s. 2903-2909
-
Tidskriftsartikel (refereegranskat)abstract
- Cr/Sc multilayers have been grown on Si substrates using dc magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. They were designed for normal reflection of the first and second orders, with multilayer periods of 1.692 and 3.381 nm, and layer thickness ratios of 0,471 and 0.237, respectively. At-wavelength soft-x-ray reflectivity measurements were carried out using a reflectometer with a compact soft-x-ray laser-plasma source. The multilayers were irradiated during growth with Ar ions, varying both in energy (9 to 113 eV) and flux, in order to stimulate the adatom mobility and improve the interface flatness. It was found that to obtain a maximum soft x-ray reflectivity with a low flux (Cr=0.76, Sc=2.5) of Ar ions a rather high energy of 53 eV was required, Such energy also caused intermixing of the layers. By the use of a solenoid surrounding the substrate, the arriving ion-to-metal flux ratio could be increased 10 times and the required ion energy could be decreased. A high flux (Cr=7.1, Sc=23.1) of low-energy (9 eV) Ar ions yielded the most favorable growth condition, limiting the intermixing with a subsistent good surface flatness.
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| 16. |
- Eriksson, Ingemar, et al.
(författare)
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Holographic measurement of thermal distortion during laser spot welding
- 2012
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Ingår i: Optical Engineering. - 0091-3286 .- 1560-2303. ; 51:3
-
Tidskriftsartikel (refereegranskat)abstract
- Welding distortion is an important engineering topic for simulation and modeling, and there is a need for experimental verification of such models by experimental studies. High-speed pulsed digital holography is proposed as a measurement technique for out-of-plane welding distortion. To demonstrate the capability of this technique, measurements from a laser spot weld are presented. A complete twodimensional deformation map with submicrometer accuracy was acquired at a rate of 1000 measurements per second. From this map, particular points of interest can be extracted for analysis of the temporal development of the final distortion geometry.
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| 17. |
- Eriksson, Ingemar, et al.
(författare)
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New high-speed photography technique for observation of fluid flow in laser welding
- 2010
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 49:10
-
Tidskriftsartikel (refereegranskat)abstract
- Recent developments in digital high-speed photography allow us to directly observe the surface topology and flow conditions of the melt surface inside a laser evaporated capillary. Such capillaries (known as keyholes) are a central feature of deep penetration laser welding. For the first time, it can be confirmed that the liquid capillary surface has a rippled, complex topology, indicative of subsurface turbulent flow. Manipulation of the raw data also provides quantitative measurements of the vertical fluid flow from the top to the bottom of the keyhole.
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| 18. |
- Fredriksson, Håkan, et al.
(författare)
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Multisource flash system for retroreflective beacon detection in CMOS cameras
- 2008
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 47, s. 103001-
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Tidskriftsartikel (refereegranskat)abstract
- We present a method for improving a flash system for retroreflective beacon detection in CMOS cameras. Generally, flash systems are designed in such a manner that makes them suited for beacon detection in a small range interval. We strive to increase the flash system range interval by exploiting the directional properties of the retroreflector. Thus, light sources placed relatively far away from the optical axis of the camera will contribute only when the retroreflector is far away. This fact can be used to compensate for the 1/distance2 dependency of optical power. We present underlying theory and formulae, then describe a flash system consisting of several light-emitting diodes that was designed by considering the presented method. Simulations show that the usable flash range of the improved system can be almost doubled compared to a general flash system. Tests were performed indicating that the presented method works according to theory and simulations.
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| 19. |
- Gontcharov, Alexander, et al.
(författare)
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Adaptive optics schemes for future extremely large telescopes
- 2002
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286. ; 41:5, s. 1065-1072
-
Tidskriftsartikel (refereegranskat)abstract
- The adaptive optics for any telescope in the 25- to 100-m class will be complex. It is believed that adaptive optics should, to the maximum extent, be designed as an integrated part of a telescope. The proposed Swedish 50-m Extremely Large Telescope is considered here to illustrate the principle of integrated adaptive optics. Two alternative designs both using the Ritchey-Chretien telescope system and laser guide star (LGS) reference sources are presented. The first design employs trombone optics, which bring the laser guide star images back to the normal Ritchey-Chretien focal surface (referred to as the RC-focus) from the LGS focal surface (referred to as the LRC-focus), and a layer-oriented wavefront sensor system optically performing the averaging "shift and add" in the final focus. According to this procedure, sensed wavefronts are overlapped with a certain mutual shift and added for estimation of wavefront average slope values, resulting in actuator commands for driving the shape of the cleformable mirrors. The second design employs a numerical "shift and add" procedure and has two wavefront sensors. The first one performs LGS sensing in an intermediate focus (LRC-focus), giving the input data for an analytical algorithm for deriving the mirror deformations to correct for atmospheric turbulence. By using an artificial laser source at the intermediate focus, the shape of the second cleformable mirror is controlled by a second wavefront sensor in the final focus. The capability of the analytical algorithm to derive the mirror corrections from the measured wavefronts ensures proper functioning of the adaptive optics system. This system has a simpler optical design compared to the first design. (C) 2002 Society of Photo-Optical Instrumentation Engineers.
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| 20. |
- Gontcharov, Alexander, et al.
(författare)
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Intrinsic apodization effect in a compact two-mirror system with a spherical primary mirror
- 2002
-
Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286. ; 41:12, s. 3111-3115
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Tidskriftsartikel (refereegranskat)abstract
- In so-called compact two-mirror focusing and afocal systems the secondary mirror is situated at the paraxial focus of the spherical primary mirror. The peculiar conelike shape of the secondary is chosen to eliminate the spherical aberration. Thus the systems are stigmatic, but they have a great offence against the sine condition (OSC), creating uneven distribution of energy on the surface of the outgoing wavefront. There is a substantial concentration of energy toward the optical axis, similar to apodization of the pupil. Calculations of the point spread function (PSF) show that in such systems, the Airy disk is slightly enlarged (at most 20%) and the second maximum (the first bright ring) can be completely suppressed. The most effective suppression of the second and higher maxima in the diffraction pattern is obtained with an imposed central obscuration ratio of 0.5 and a primary mirror focal ratio of 2. Compact two-mirror afocal and focusing systems have intrinsic apodization, enabling modification of the diffraction pattern without the use of a variable transmission filter or coating at the pupil. (C) 2002 Society of Photo-Optical Instrumentation Engineers.
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| 21. |
- Granberg, H., et al.
(författare)
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Forward scattering of fiber-containing surfaces studied by 3-D reflectance distribution simulations and measurements
- 2003
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 42:8, s. 2384-2390
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have shown that the angular distribution of diffuse reflectance, obtained from bidirectional reflectance distribution function (BRDF) measurements, differs strongly between paper sheets with and without fibers present in the top surface layer. For fiber-containing surfaces, in contrast to pigment-coated paper surfaces, there is a distinct forward scattering at angles much larger than the specular reflection angle. In the search for an explanation of this phenomenon, we have made calculations of reflectance distributions of a simulated paper web, containing randomly distributed hollow fibers. We did this on the assumption that fibers present in paper are considerably larger than the wavelength of visible light, and that the surface microroughness of the fibers can be treated as a diffraction broadening superposed on the ray calculated reflectance distribution. We investigate whether the structural shape and distribution of wood fibers can explain some of the observed forward-scattering phenomenon. We also compare these Monte-Carlo ray tracing calculations qualitatively with experimental BRDF measurements of the diffuse reflectance from a fiber-containing surface. From the calculations we found that the reflection at the inner fiber wall of the hollow fibers constituting the topmost layer plays a major role in forming a forward-scattering reflectance distribution. We also found that the Monte-Carlo-calculated bulk scattering distribution, i.e., the distribution of reflected light after a large number of reflections within the web structure, tended to be elongated perpendicular to the sheet plane of the fiber web, rather than being uniform.
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| 22. |
- Grönwall, Christina, et al.
(författare)
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Influence of Laser Radar Sensor Parameters on Range Measurement and Shape Fitting Uncertainties
- 2007
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Ingår i: Optical Engineering. - : SPIE - International Society for Optical Engineering. - 0091-3286 .- 1560-2303. ; 46:10
-
Tidskriftsartikel (refereegranskat)abstract
- Inobject/target reconstruction and recognition based on laser radar data, the range value's accuracy is important. The range data accuracy depends on the accuracy in the laser radar's detector, especially the algorithm used for time-of-flight estimation. In this paper, a general direct-detection laser radar system applicable for hard-target measurements is modeled. The time- and range-dependent laser radar cross sections are derived for some simple geometric shapes (plane, cone, sphere, and paraboloid). The cross-section models are used, in simulations, to find the proper statistical distribution of uncertainties in time-of-flight range estimations. Three time-of-flight estimation algorithms are analyzed: peak detection, constant-fraction detection, and matched filter. The detection performance for various shape conditions and signal-to-noise ratios is analyzed. Two simple shape reconstruction examples are shown, and the detectors' performance is compared with the Cramér-Raolower bound. The performance of the peak detection and the constant-fraction detection is more dependent on the shape and noise level than that of the matched filter. For line fitting the matched filter performs close to the Cramér-Rao lower bound.
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| 23. |
- Grönwall, Christina, et al.
(författare)
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Spatial filtering for detection of partly occluded targets
- 2011
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 50:4, s. 047201-1-047201-13
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Tidskriftsartikel (refereegranskat)abstract
- A Bayesian approach for data reduction based on spatial filtering is proposed that enables detection of targets partly occluded by natural forest. The framework aims at creating a synergy between terrain mapping and target detection. It is demonstrates how spatial features can be extracted and combined in order to detect target samples in cluttered environments. In particular, it is illustrated how a priori scene information and assumptions about targets can be translated into algorithms for feature extraction. We also analyze the coupling between features and assumptions because it gives knowledge about which features are general enough to be useful in other environments and which are tailored for a specific situation. Two types of features are identified, nontarget indicators and target indicators. The filtering approach is based on a combination of several features. A theoretical framework for combining the features into a maximum likelihood classification scheme is presented. The approach is evaluated using data collected with a laser-based 3-D sensor in various forest environments with vehicles as targets. Over 70% of the target points are detected at a false-alarm rate of <1%. We also demonstrate how selecting different feature subsets influence the results.
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| 24. |
- Hansson, Göran
(författare)
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Solid state multiple-beam laser with tunable wavelength difference between beams
- 2000
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 39:10, s. 2700-2704
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Tidskriftsartikel (refereegranskat)abstract
- A diode laser pumped solid state laser design capable of generating several simultaneously emitted spatially separate and wavelength tunable beams is presented. The laser design was demonstrated in a dual-beam configuration using Tm,Ho:YLF as laser material. Laser oscillation in two TEM00, longitudinal multimode cw beams of 80-mW maximum output power was demonstrated. The wavelength difference between the beams was tuned over a 15-nm-wide range using one solid etalon as a tuning element.
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| 25. |
- Heimsten, Rikard, et al.
(författare)
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Suppressing low-order eigenmodes with local control for deformable mirrors
- 2012
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Ingår i: Optical Engineering. - 0091-3286. ; 51:2
-
Tidskriftsartikel (refereegranskat)abstract
- To improve the mechanical characteristics of actively controlled continuous faceplate deformable mirrors in adaptive optics, a strategy for reducing crosstalk between adjacent actuators and for suppressing low-order eigenmodes is proposed. The strategy can be seen as extending Saint-Venant's principle beyond the static case, for small local families of actuators. An analytic model is presented, from which we show the feasibility of the local control. Also, we demonstrate how eigenmodes and eigenfrequencies are affected by mirror parameters, such as thickness, diameter, Young's modulus, Poisson's ratio, and density. This analysis is used to evaluate the design strategy for a large deformable mirror, and how many actuators are needed within a family. (c) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.OE.51.2.026601]
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| 26. |
- Hemberg, Oskar, et al.
(författare)
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A Liquid-Metal-Jet Anode X-Ray Tube
- 2004
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 43:7, s. 1682-1688
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Tidskriftsartikel (refereegranskat)abstract
- We describe a novel electron-impact x-ray source based on a high-speed liquid-metal-jet anode. Thermal power load calculations indicate that this new anode concept potentially could increase the achievable brightness in compact electron-impact x-ray sources by more than a factor 100 compared to current state-of-the-art rotating-anode or microfocus sources. A first, successful, low-power proof-of-principle experiment is described and the feasibility of scaling to high-brightness and high-power operation is discussed. Some possible applications that would benefit from such an increase in brightness are also briefly
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| 27. |
- Hermann, D. S., et al.
(författare)
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Novel passive polymer waveguides integrated with electro-optically active ferroelectric liquid crystals
- 2001
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 40:10, s. 2188-2198
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Tidskriftsartikel (refereegranskat)abstract
- We report the preparation and characterization of novel isotropic polymer slab waveguides made by photochemical crosslinking, and their integration with a ferroelectric liquid crystal in an integrated electro-optic modulator. The refractive index of the passive copolymer material in the device was controlled by the copolymer composition, and good agreement between measured and calculated effective indices for the guided modes of polymer films was obtained. The active ferroelectric liquid crystal exhibited a refractive index change of Deltan approximate to0.10 upon application of an ac voltage of +/- 30 V, giving an electro-optic modulation of the input TE0-mode with a contrast ratio of 11:1 and only a small polarization conversion into TM output light.
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| 28. |
- Hyyppä, Kalevi
(författare)
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Signal response of a laser beam scanner
- 1994
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 33:8, s. 2770-2776
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Tidskriftsartikel (refereegranskat)abstract
- A laser beam scanner, used as an angle measuring device in a particular navigation system for mobile robots, has been developed. It measures heading angles to beacons made of vertical stripes of retroreflective tape. Expressions giving the received power and energy in the pulse, which is generated when a beacon is traversed by the laser beam, are given. Measurements support the derived expressions. The shape and amplitude of the pulse are functions of the range R to the beacon, but at long range the pulse shape and width become independent of range while the dependence of the received amplitude on range becomes R-3. At long range the pulse shape is determined by the Gaussian irradiance distribution in the laser beam and the pulse width is governed by the laser beam divergence and the scanning speed. Design rules for the optimum field of view of the receiving optics and for an electrical filter, which maximizes the signal-to-noise ratio, are proposed. An expression giving a conservative estimate of the signal-to-noise ratio is derived.
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| 29. |
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| 30. |
- Hällstig, Emil, et al.
(författare)
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Retrocommunication utilizing electroabsorption modulators and non-mechanical beam steering
- 2005
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 44:4, s. 045001-
-
Tidskriftsartikel (refereegranskat)abstract
- A novel retrocommunication link utilizing reflective multiplequantum well (MQW) optical modulators and nonmechanical beamsteering and tracking is demonstrated. Large aperture reflective MQWmodulators using AlGaAs/GaAs are optimized and manufactured. Themodulators exhibit a contrast ratio larger than 4:1 and a modulationbandwidth of 10 MHz. Nonmechanical beam steering and tracking arestudied using nematic liquid crystal (NLC) spatial light modulators(SLMs). The communication link is comprised of a retromodulating arraywith four MQW modulators and a transceiver using a NLC SLM for beamsteering and tracking. Transfer of audio, real-time image data and pseudorandombit sequences over 100-m range while tracking the movingretromodulator is shown. The link is capable of transferring data at approximately8 Mbps.
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| 31. |
- Jonsson, Magnus, 1969-
(författare)
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Two fiber-ribbon ring networks for parallel and distributed computing systems
- 1998
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Ingår i: Optical Engineering. - Redondo Beach, Calif. : Society of photo-optical instrumentation engineers (SPIE). - 0091-3286 .- 1560-2303. ; 37:12, s. 3196-3204
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Tidskriftsartikel (refereegranskat)abstract
- Ring networks made of fiber-ribbon point-to-point links are proposed. The first network is a control-channel based network in which one fiber in each link joins with others to form a control-channel ring. This ring improves performance of the network by sending medium access control information immediately before the data transmissions. High throughputs can be achieved in the network due to pipelining, i.e., several packets can travel through the network simultaneously but in different segments of the ring. The network can meet tough performance demands in, e.g., massively parallel signal processing systems, which is shown by example. Also, real-time demands can be met using slot reserving. The network, called CC-FPR (control-channel based fiber-ribbon pipeline ring), can be built today using off-the-shelf fiber optic components. The increasingly good price/performance ratio for fiber-ribbon links indicates a high potential for the success of the proposed kind of networks; a prototype is currently under development. The second network is similar to first except that it divides the network into two subnetworks, one for packet-switched traffic and one for circuit-switched traffic. When the main data flow in the network does not change rapidly, this is a good choice for a simple but powerful network.
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| 32. |
- Kaestner, Anders P., et al.
(författare)
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Estimating the relative shrinkage profile of newsprint
- 2003
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Ingår i: Optical Engineering. - Redondo Beach, Calif. : SPIE, The International Society for Optical Engineering. - 0091-3286 .- 1560-2303. ; 42:5, s. 1467-1475
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Tidskriftsartikel (refereegranskat)abstract
- When water is removed from the paper during paper making, a dimensional change occurs in which the paper shrinks in the direction perpendicular to the direction of processing. The dimensional changes vary across the web and influence, e.g., the surface and compression properties of the paper; they also complicate the control of the paper machine. In this article, a robust method for estimating the relative shrinkage profile is presented. The method is based on a one-dimensional recording of the imprints from the forming fabric, using a fluorescence technique. The recording is transformed into a time-frequency spectrum, on which three different frequency estimators have been evaluated. In simulations on synthetic data and measurements on paper profiles the estimator that maximizes the correlation energy showed the most robust and accurate performance of the methods evaluated, even at a low signal-to-noise ratio.
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| 33. |
- Kalustova, Daria, et al.
(författare)
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Color temperature tunable RGBW cluster with optimize color rendering and efficacy
- 2023
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Ingår i: Optical Engineering. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 0091-3286 .- 1560-2303. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- Our work is devoted to the optimization of 4-component RGBW smart lighting systems that are able to obtain the resulting white light with a combination of high color rendering and luminous efficacy for a certain fixed correlated color temperature. Three approaches for the determination of the optimal brightness contributions of the light emitting diodes (LEDs) are studied. They are accordingly based on: (1) maximization of the color rendering, (2) prioritizing to reduce the color rendering maximum by 1 to 6 units to increase luminous efficacy, and (3) getting a constant value of RGB contribution and luminous efficacy while maintaining high color rendering. A comparison of the three systems with different base white LEDs is demonstrated. The obtained theoretical results are verified experimentally.
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| 34. |
- Kalustova, Daria, et al.
(författare)
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Red, green, blue, and white clusters for daylight reproduction
- 2020
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Ingår i: Optical Engineering. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 0091-3286 .- 1560-2303. ; 59:5
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Tidskriftsartikel (refereegranskat)abstract
- Daylight is an inherent attribute of a sustainable building. Artificial reproduction of natural illumination under varying needs and environmental conditions has been made possible after the appearance of the new wave of solid-state light sources. Our work is devoted to the development of white light-emitting diode (LED) clusters consisting of red, green, blue, and white (RGBW) LEDs for implementation in a smart lighting system that is able to reproduce light with correlated color temperature (CCT) similar to daylight, high values of color rendering index, and luminous efficacy. A method for determination of the optimal contribution of each of the four LEDs is demonstrated and discussed. We show that only three LEDs-green, blue, and white (no red) can be used in many cases for reproducing daylight. Both luminous efficacy of radiation and actual luminous efficacy of the considered RGBW clusters as functions of the CCT are analyzed. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE).
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| 35. |
- Kaplan, Alexander
(författare)
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Analysis and modeling of a high-power Yb:fiber laser beam profile
- 2011
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 50:5
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Tidskriftsartikel (refereegranskat)abstract
- Recently the fiber and the disk laser have been developed as advanced high power lasers of continuous wave type. Their beams are fiber-guided. Their low beam parameter product determines the focused beam as a high power density tool for laser materials processing. The lateral and axial power density distribution is crucial for the process. The measurement of a focused Yb:fiber laser beam is compared with its theoretical profile. While a Gauss beam describes the real beam in the far field, in the vicinity of the focus the beam is similar to a top-hat profile. In particular, the peak power density is lower around the focus than for a Gaussian beam. This provides a flatter, less varying optical tool along a certain axial range. A suitable model of the focused laser beam is achieved by superposition of a Gauss beam with a second but negative Gauss beam, each with matched parameters for power, spot diameter, and Rayleigh length. Owing to its much better accuracy with less than a 20% error, the model beam is applicable, e. g., for simulation of the welding process
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| 36. |
- Kazmierczak, Andrzej, et al.
(författare)
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Light coupling and distribution for Si3N4/SiO2 integrated multichannel single-mode sensing system
- 2009
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 48:1
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Tidskriftsartikel (refereegranskat)abstract
- We present an efficient and highly alignment-tolerant light coupling and distribution system for a multichannel Si3N4/SiO2 single-mode photonics sensing chip. The design of the input and output couplers and the distribution splitters is discussed. Examples of multichannel data obtained with the system are given.
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| 37. |
- Khodadad, Davood, et al.
(författare)
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Dual-wavelength digital holographic shape measurement using speckle movements and phase gradients
- 2013
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Ingår i: Optical Engineering. - : SPIE - International Society for Optical Engineering. - 0091-3286 .- 1560-2303. ; 52:10
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Tidskriftsartikel (refereegranskat)abstract
- A new method to measure shape by analyzing the speckle movements in images generated by numerical propagation from dual-wavelength holograms is presented. The relationship of the speckle movements at different focal distances is formulated, and it is shown how this carries information about the surface position as well as the local slope of the object. It is experimentally verified that dual-wavelength holography and numerically generated speckle images can be used together with digital speckle correlation to retrieve the object shape. From a measurement on a cylindrical test object, the method is demonstrated to have a random error in the order of a few micrometers.
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| 38. |
- Khrennikov, Andrei, 1958-
(författare)
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Role of detectors and their proper calibration in inter-relation between classical and quantum optics
- 2012
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Ingår i: Optical Engineering. - : SPIE - International Society for Optical Engineering. - 0091-3286 .- 1560-2303. ; 51:6, s. Article ID: 069001-
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Tidskriftsartikel (refereegranskat)abstract
- We describe quantum theory by using a complex valued random signal, which is (coherently) averaged over a time window, and a photon click is defined as the energy of this averaged signal surpassing a detector threshold. The random signal is modeled as white noise but grows over time s (proportional to s). Eventually this random signal will lead to a detector “click” defined by a detector threshold condition, at which point the random signal is reset. Further we proceed by analysing correlations and finally by modeling the quantum state of an entangled pair by a complex valued correlation function.
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| 39. |
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| 40. |
- Li, Yanzeng, et al.
(författare)
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Near-infrared transmittance enhancement using fully conformal antireflective structured surfaces on microlenses fabricated by direct laser writing
- 2019
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Ingår i: Optical Engineering. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 0091-3286 .- 1560-2303. ; 58:1
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Tidskriftsartikel (refereegranskat)abstract
- Structured surfaces composed of subwavelength-sized features offer multifunctional properties including antireflective characteristics that are increasingly important for the development of micro-optical components. Here, three-dimensional (3-D) direct laser writing, via two-photon polymerization, is used to fabricate planoconvex spherical microlenses with antireflective structured surfaces. The surfaces are composed of subwavelength-sized conicoid structures, which are arranged fully conformal to the convex surface of the microlenses. The dimensions of the conicoid structures are optimized to effectively reduce Fresnel reflection loss over a wide band in the near-infrared spectral range from 1.4 to 2.2 mu m, with a maximum reduction at 1.55 mu m. Infrared reflection and transmission measurements are used, in combination with 3-D finite element calculations, to investigate the performance of the microlenses. The experimental results reveal that in the spectral range from 1.4 to 2.2 mu m an effective suppression of the Fresnel reflection loss at the convex surface of spherical microlenses can be achieved. The transmittance enhancement is ranging from 1% to 3% for spherical microlenses with antireflective structured surfaces, in comparison to an uncoated reference. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)
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| 41. |
- Lindstrom, T, et al.
(författare)
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Total integrated scattering from transparent substrates in the infrared region: validity of scalar theory
- 2000
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 39:2, s. 478-487
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Tidskriftsartikel (refereegranskat)abstract
- Integrated light scattering, from thin, transparent silicon wafers with different front and backside surface roughness is investigated. The measurements are made at near normal incidence in the IR wavelength region 5 to 20 μm using an integrating sphere. A method to separate the scattering contribution from each interface for measurements on transparent samples is introduced. Scalar scattering theory is used to calculate the effective root mean square roughness from reflectance and transmittance measurements, and these values are compared to profilometer data, correcting for the different bandwidth limits. Scattering measurements are performed with both the rough and the smooth surface of the wafer oriented toward the light source, which results in additional knowledge. The maximum ratio between the root mean square roughness and the wavelength of the light, to be used in scalar theory, is found to be considerably higher for the transmittance case than for the reflectance case. In agreement with theory, the calculated root mean square roughness is found to be proportional to the refractive index of incident medium in reflectance, and to the difference in refractive indices of incident and refracting medium for the transmittance case.
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| 42. |
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| 43. |
- Lofdahl, M. G., et al.
(författare)
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Algorithm for resolving 2 pi ambiguities in interferometric measurements by use of multiple wavelengths
- 2001
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Ingår i: Optical Engineering. - 0091-3286 .- 1560-2303. ; 40:6, s. 984-990
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Tidskriftsartikel (refereegranskat)abstract
- Measurement of differences in optical path length in monochromatic light with any interferometric method is insensitive to errors that are whole numbers of waves. If measurements are performed in several wavelengths, this ambiguity can be resolved. We present a general algorithm for finding the correct distance post facto, given multiple measurements in different wavelengths. Applied to piston measurements of a segmented mirror, the capture range of a wavefront sensor can be extended from +/- half a wave to several waves. The extended capture range can be calculated and depends on the selection of wavelengths used for measurements and the expected accuracy of the method used.
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| 44. |
- Lundén, Hampus, et al.
(författare)
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How to assess good candidate molecules for self-activated optical power limiting
- 2018
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Ingår i: Optical Engineering. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 0091-3286 .- 1560-2303. ; 57:3
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Tidskriftsartikel (refereegranskat)abstract
- Reverse saturable absorbers have shown great potential to attenuate laser radiation. Good candidate molecules and various particles have successfully been incorporated into different glass matrices, enabling the creation of self-activated filters against damaging laser radiation. Although the performance of such filters has been impressive, work is still ongoing to improve the performance in a wider range of wavelengths and pulse widths. The purpose of this tutorial is, from an optical engineering perspective, to give an understanding of the strengths and weaknesses of this class of smart materials, how relevant photophysical parameters are measured and influence system performance and comment on the pitfalls in experimental evaluation of materials. A numerical population model in combination with simple physical formulas is used to demonstrate system behavior from a performance standpoint. Geometrical reasoning shows the advantage of reverse saturable absorption over nonlinear scattering due to a fraction of scattered light being recollected by imaging system optics. The numerical population model illustrates the importance of the optical power limiting performance during the leading edge of a nanosecond pulse, which is most strongly influenced by changes in the two-photon absorption cross section and the triplet linear absorption cross section for a modeled Pt-acetylide. This tutorial not only targets optical engineers evaluating reverse saturable absorbing materials but also aims to assist researchers with a chemistry background working on optical power limiting materials. We also present photophysical data for a series of coumarins that can be useful for the determination of quantum yields and two-photon cross sections and show examples of characterization of molecules with excited triplet states. (c) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).
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| 45. |
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| 46. |
- Marklund, Olov, et al.
(författare)
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Robust unwrapping algorithm for three-dimensional phase volumes of arbitrary shape containing knotted phase singularity loops
- 2007
-
Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 46:8
-
Tidskriftsartikel (refereegranskat)abstract
- The extension of path-independent 2-D phase unwrapping algorithms, based on placement of branch cut lines between phase singularities of opposite sign, was recently proposed for phase volumes in a paper by Huntley. In 3-D, the singularities were shown to form closed loops, and path independence was achieved by placing branch cut surfaces across the loops. In the current work, we describe in detail an optimized and extended version of Huntley's algorithm. It deals in particular with two aspects that are essential for practical phase volumes: 1. how to close partial loops that pass through arbitrary boundaries separating valid and invalid phase data, and 2. how to select the set of loops having the shortest length. The second algorithm is necessary to deal with ambiguous cases that can arise when the singularities form knots, i. e., two loops pass through a single phase volume element. The performance of the algorithm is demonstrated on 3-D phase maps from two types of medical imaging data: medical resonance imaging (MRI) and x-ray interferometry.
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| 47. |
- Melin, L. Gunnar
(författare)
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High-speed moire photography for studying dynamic properties in carbon fiber composites
- 1998
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 37:2, s. 642-649
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Tidskriftsartikel (refereegranskat)abstract
- In the experiments reported here, a moire technique for measuring in-plane displacements was applied to the study of carbon/epoxy composite specimens deformed at high strain rates. The moire fringes were analyzed using the Fourier transform method. The measurements show that the material behaves in a linearly elastic manner up to fracture. Crack propagation rates of about 2000 m/s in the grating plane were observed. The optical aspects of the experiment are discussed
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| 48. |
- Metaferia, Wondwosen, et al.
(författare)
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Demonstration of a quick process to achieve buried heterostructure quantum cascade laser leading to high power and wall plug efficiency
- 2014
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 53:8, s. 087104-
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Tidskriftsartikel (refereegranskat)abstract
- Together with the optimal basic design, buried heterostructure quantum cascade laser (BH-QCL) with semi-insulating regrowth offers a unique possibility to achieve an effective thermal dissipation and lateral single mode. We demonstrate here the realization of BH-QCLs with a single-step regrowth of highly resistive (>1 x 10(8) ohm . cm) semi-insulating InP: Fe in <45 min for the first time in a flexible hydride vapor phase epitaxy process for burying ridges etched down to 10 to 15 mu m depth, both with and without mask overhang. The fabricated BH-QCLs emitting at similar to 4.7 and similar to 5.5 mu m were characterized. 2-mm-long 5.5-mu m lasers with a ridge width of 17 to 22 mu m, regrown with mask overhang, exhibited no leakage current. Large width and high doping in the structure did not permit high current density for continuous wave (CW) operation. 5-mm-long 4.7-mu m BH-QCLs of ridge widths varying from 6 to 14 mu m regrown without mu mask overhang, besides being spatially monomode, TM00, exhibited wall plug efficiency (WPE) of similar to 8 to 9% with an output power of 1.5 to 2.5 W at room temperature and under CW operation. Thus, we demonstrate a quick, flexible, and single-step regrowth process with good planarization for realizing buried QCLs leading to monomode, high power, and high WPE.
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| 49. |
- Mohan, N.K., et al.
(författare)
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Dual-beam symmetric illumination-observation TV holography system for measurements
- 2001
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286 .- 1560-2303. ; 40:12, s. 2780-2787
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Tidskriftsartikel (refereegranskat)abstract
- The Leendertz dual-beam symmetric illumination-normal observation arrangement is widely employed for real time evaluation of in-plane displacement components as well as surface shape. Instead of observing along the optical axis, we have examined the Leendertz arrangement by observing the scattered light along the direction of the illumination beams, and imaged it as two separate images onto the photo sensor of a CCD camera. The interferometer is a combination of two channels, each of which measures independently and simultaneously the information pertaining to either the in-plane displacement component of a deformation vector, or the surface relief variation of a three-dimensional object. In addition, a summary of possible measurements that can be carried out from the present arrangement is also highlighted. Experimental results using a four-frame phase shifting technique are illustrated
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| 50. |
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