Showing papers on "Cardinal point published in 2008"
TL;DR: A fluorescence microscope that creates nearly spherical focal spots of 40–45 nm (λ/16) in diameter is introduced, which unravels the interior of cells noninvasively, uniquely dissecting their sub-λ–sized organelles.
Abstract: The resolution of any linear imaging system is given by its point spread function (PSF) that quantifies the blur of an object point in the image. The sharper the PSF, the better the resolution is. In standard fluorescence microscopy, however, diffraction dictates a PSF with a cigar-shaped main maximum, called the focal spot, which extends over at least half the wavelength of light (lambda = 400-700 nm) in the focal plane and >lambda along the optical axis (z). Although concepts have been developed to sharpen the focal spot both laterally and axially, none of them has reached their ultimate goal: a spherical spot that can be arbitrarily downscaled in size. Here we introduce a fluorescence microscope that creates nearly spherical focal spots of 40-45 nm (lambda/16) in diameter. Fully relying on focused light, this lens-based fluorescence nanoscope unravels the interior of cells noninvasively, uniquely dissecting their sub-lambda-sized organelles.
483 citations
Patent•
25 Mar 2008
TL;DR: In this paper, a low-beam light distribution pattern is formed by turning on a first light source unit and a high-beam lighting distribution pattern was formed by additionally turning on the second LBS unit, which vertically strides over the cutoff line of the LBS distribution pattern.
Abstract: A low beam light distribution pattern is formed by turning on a first light source unit and a high beam light distribution pattern is formed by additionally turning on a second light source unit. The second reflector of the second light source unit has reflecting faces of vertical cross-sectional shapes formed by two types of ellipses whose first focal point is on a center of emission of a second light-emitting element and whose second focal points are respectively positioned on points A, B. The additional lens whose rear focal points are on the second focal points A, B is arranged on a circumference of a projection lens. When the second light source unit is turned on, a high beam additional light distribution pattern is formed that vertically strides over the cutoff line of the low beam light distribution pattern.
93 citations
TL;DR: The application results using the dot array target showed that the Wiener filter is a very effective tool for processing holography-related images and the effects of the dot size and the object distance on the errors in the determination of the focal plane by the CC method were investigated.
Abstract: The correlation coefficient (CC) method, which was proposed by our research group, is applied to digital particle holography to locate the focal plane of particles. It uses the fact that the CC is maximum at the focal plane. The factors influencing this method are discussed with a numerical simulation of holograms. For real holograms, the Wiener filter was proposed to process both recorded holograms and reconstructed images. The application results using the dot array target showed that the Wiener filter is a very effective tool for processing holography-related images. The effects of the dot size and the object distance on the errors in the determination of the focal plane by the CC method were investigated by using the calibration target.
85 citations
Patent•
5 Nov 2008TL;DR: In this article, a headlight consisting of a cup-shaped reflector with two focal points is described, which can be adjusted in several rotating positions and has in each rotating position a focal line providing a light-and-dark border of a light figure.
Abstract: The invention relates to a headlight comprising a cup-shaped reflector (1) with two focal points. The rotation axis (8) of a diaphragm shaft (3) disposed between a lens (2) and the reflector extends horizontally and transversally in relation to the optical axis. The diaphragm shaft can be adjusted in several rotating positions and has in each rotating position a focal line (4, 5, 6, 7) providing a light-and-dark border (19, 20, 21, 22) of a light figure (23, 24, 25, 26). The surface of the sheath (9) of the diaphragm shaft (3) extends at least in a surface section connecting two focal lines, in an irregular manner and deviating from a cylindrical surface (18).
81 citations
TL;DR: In this paper, the performance of the optical vortex coronagraph was compared to some other designs, showing that it performs similarly in this situation as other coronagraphs, and quantified with both numerical and analytical calculations.
Abstract: The optical vortex coronagraph is potentially a remarkably effective device, at least for an ideal unobstructed telescope. Most ground-based telescopes however suffer from central obscuration and also have to operate through the aberrations of the turbulent atmosphere. This paper analyses the performance of the optical vortex in these circumstances and compares to some other designs, showing that it performs similarly in this situation. There is a large class of coronagraphs of this general type, and choosing between them in particular applications depends on details of performance at small off-axis distances and uniformity of response in the focal plane. These are quantified with both numerical and analytical calculations.
63 citations
TL;DR: The test results validate the pixel design and demonstrate that lossy prediction based focal plane image compression can be realized inside the sensor pixel array to achieve a high frame rate with much lower data readout volume.
Abstract: An alternative image decomposition method that exploits prediction via nearby pixels has been integrated on the CMOS image sensor focal plane. The proposed focal plane decomposition is compared to the 2-D discrete wavelet transform (DWT) decomposition commonly used in state of the art compression schemes such as SPIHT and JPEG2000. The method achieves comparable compression performance with much lower computational complexity and allows image compression to be implemented directly on the sensor focal plane in a completely pixel parallel structure. A CMOS prototype chip has been fabricated and tested. The test results validate the pixel design and demonstrate that lossy prediction based focal plane image compression can be realized inside the sensor pixel array to achieve a high frame rate with much lower data readout volume. The features of the proposed decomposition scheme also benefit real-time, low rate and low power applications.
50 citations
TL;DR: The proposed LC lens with proposed electrodes improves the central intensity of electric field which leads to better focusing quality and is capable of achieving relative higher focusing power than past studies with lower applied voltage.
Abstract: Aiming to equip commercial camera modules, such as the optical imaging systems with a CMOS sensor module in 3 Mega pixels, an ultra thin liquid crystal lens with designed hole-and-ring electrodes is proposed in this study to achieve high focusing power. The LC lens with proposed electrodes improves the central intensity of electric field which leads to better focusing quality. The overall thickness of the LC lens can be as thin as 1.2 mm and the shortest focal length of the 4 mm-aperture lens occurs at 20 cm under an applied voltage of 30 V at 1 KHz. The inner ring electrode requires only 40% of applied voltage of the external hole electrode. The applied voltages for this internal ring and external hole electrodes can simply be realized by a pre-designed parallel resistance pair and a single voltage source. Experiments are conducted for validation and it shows that the designed LC lens owns good image clearness and contrast at the focal plane. The proposed design reduces the thickness of LC lens and is capable of achieving relative higher focusing power than past studies with lower applied voltage.
43 citations
TL;DR: In this paper, a cross-convolutional image subtraction algorithm was proposed to solve the problem of sparse stellar images. But the computational efficiency is comparable with similar procedures currently in use, and it requires high quality reference images for comparison.
Abstract: In recent years, there has been a proliferation of wide-field sky surveys to search for a variety of transient objects. Using relatively short focal lengths, the optics of these systems produce undersampled stellar images often marred by a variety of aberrations. As participants in such activities, we have developed a new algorithm for image subtraction that no longer requires high-quality reference images for comparison. The computational efficiency is comparable with similar procedures currently in use. The general technique is cross-convolution: two convolution kernels are generated to make a test image and a reference image separately transform to match as closely as possible. In analogy to the optimization technique for generating smoothing splines, the inclusion of an rms width penalty term constrains the diffusion of stellar images. In addition, by evaluating the convolution kernels on uniformly spaced subimages across the total area, these routines can accommodate point-spread functions that vary considerably across the focal plane.
43 citations
TL;DR: It is shown that the obtained FTIR-FPA can be described by intrinsic parameters such as an optical path difference and a so-called spectrometric efficiency.
Abstract: A novel configuration of stationary Fourier transform infrared (FTIR) spectrometer is presented. Contrary to classic configurations, the interferometer is directly integrated in the focal plane array (FPA) during its process of fabrication. A first, to the best of our knowledge, demonstration of the spectrometric function has been achieved departing from a well-known structure of an HgCdTe photodetector. We show that the obtained FTIR-FPA can be described by intrinsic parameters such as an optical path difference and a so-called spectrometric efficiency. First experimental results are presented.
42 citations
TL;DR: In this article, the authors used a flat target with colored stripes placed close to the focal plane and a digital camera located at an observation point on the optical axis at some distance from it.
Abstract: A new short, yet highly accurate method for measuring the slope errors of parabolic dish concentrators has been developed. This method uses a flat target with colored stripes that is placed close to the focal plane and a digital camera located at an observation point on the optical axis at some distance from it. A specially developed image analysis algorithm detects the different colors in the images of the reflection of the target in the concentrator and assigns them their known position on the color target. This information, along with the geometric relationship between the components of the measurement setup and the theoretical parabolic shape of the concentrator, is used to calculate the normal vectors of the concentrator surface. From these normal vectors the radial and tangential slopes can be calculated and compared to the design values of the concentrator. The resulting slope errors not only give the total concentrator error for general characterization of the dish, but also indicate systematic errors in fabrication and mounting with high spatial resolution.
In order to verify the quality of the results obtained, a ray-tracing code was developed that calculates the flux distribution on planes perpendicular to the optical axis. Measured slope errors of a DISTAL-2 dish concentrator are presented and the calculated flux distributions are compared to measured flux distributions. The comparison shows excellent agreement in the flux distribution on the absorber plane. This verifies the promising potential of this method for fast, highly precise measurement of imperfections in dish concentrator shape.
42 citations
Patent•
2 Dec 2008
TL;DR: In this article, an illumination unit consisting of a strip-type optical wave guide and an imagining means was proposed for high light efficiency with a reduced number of primary light sources, enabling the production of a coherent plane wave field having a temporal and spatial coherence required for holographic reconstructions.
Abstract: The invention relates to an illumination unit comprising a strip-type optical wave guide and an imagining means, and providing a very high light efficiency with a reduced number of primary light sources. Said illumination unit enables the production of a coherent plane wave field having a temporal and spatial coherence required for holographic reconstructions. The strip-type optical wave guide (3) contains a number of extraction elements (4) for extracting injected coherent light guided into an observer plane by imaging elements via a controllable light modulation means. During the injection of light, the extraction elements form a grid of secondary light sources which are arranged in the front focal plane of the imaging elements and carry out the spatial coherence in at least one dimension. A secondary light source and an imaging element are associated with each other in order to guide the extracted light through the controllable light modulation means in a collimated manner. Different embodiment examples of optical wave guides and extraction elements are described. The invention is used for a holographic display appliance for reconstructing a 3D scene.
TL;DR: A full model of image formation is introduced which takes into account the effects of isotropic emission and defocus and is used to obtain a weighting function which is used in a variation of the FBP algorithm called weighted filtered backprojection (WFBP).
Abstract: Reconstructing images from a set of fluorescence optical projection tomography (OPT) projections is a relatively new problem. Several physical aspects of fluorescence OPT necessitate a different treatment of the inverse problem to that required for non-fluorescence tomography. Given a fluorophore within the depth of field of the imaging system, the power received by the optical system, and therefore the CCD detector, is related to the distance of the fluorophore from the objective entrance pupil. Additionally, due to the slight blurring of images of sources positioned off the focal plane, the CCD image of a fluorophore off the focal plane is lower in intensity than the CCD image of an identical fluorophore positioned on the focal plane. The filtered backprojection (FBP) algorithm does not take these effects into account and so cannot be expected to yield truly quantitative results. A full model of image formation is introduced which takes into account the effects of isotropic emission and defocus. The model is used to obtain a weighting function which is used in a variation of the FBP algorithm called weighted filtered backprojection (WFBP). This new algorithm is tested with simulated data and with experimental data from a phantom consisting of fluorescent microspheres embedded in an agarose gel.
TL;DR: In this paper, angle-resolved diffraction signatures are obtained from grating targets by imaging the back focal plane of a brightfield microscope that has been modified to allow selection of the angular distribution and polarization of the incident illumination.
Abstract: We demonstrate optical critical dimension measurement of lines in silicon grating targets using back focal plane scatterfield icroscopy. In this technique, angle-resolved diffraction signatures are obtained from grating targets by imaging the back focal plane of a brightfield microscope that has been modified to allow selection of the angular distribution and polarization of the incident illumination. The target line profiles, including critical dimension linewidth and sidewall angle, are extracted using a scatterometry method that compares the diffraction signatures to a library of theoretical signatures. Because we use the zero-order component of the diffraction, the target features need not be resolved in order to obtain the line profile. We extracted line profiles from two series of targets with fixed pitch but varying linewidth: a subresolution 300-nm-pitch series, and a resolved 600-nm-pitch series. Linewidths of 131 nm to 139 nm were obtained, with nanometer-level sensitivity to linewidth, and a linear relationship of linewidth obtained from scatterfield microscopy to linewidth measured by scanning electron microscopy was demonstrated. Conventional images can be easily collected on the same microscope, providing a powerful tool for combining imaging metrology with scatterometry for optical critical dimension measurement.
TL;DR: The rigorous numerical results indicate that the designed BSDLs indeed have long focal depth and high transverse resolution by modulating the binary sub-wavelength characteristic sizes.
Abstract: This study explores two-dimensional binary sub-wavelength diffractive lenses (BSDLs) for implementing long focal depth and high transverse resolution based on the rigorous electromagnetic theory and the finite-difference time-domain method. Focusing performances, such as the actual focal depth, the ratio between the focal depth of the designed BSDL and the focal depth of the conventional sub-wavelength lens and the spot size of the central lobe at the actual focal plane, for different f-numbers, have been studied in the case of TE incidence polarization wave. The rigorous numerical results indicate that the designed BSDLs indeed have long focal depth and high transverse resolution by modulating the binary sub-wavelength characteristic sizes. Because BSDLs have the ability for monolithic integration and can require only single step fabrication, the investigations may provide useful information for BSDLs’ application in micro-optical systems.
TL;DR: In this paper, a more accurate description of the three-dimensional DDPIV measurement system can be developed by introducing a measurement volume based on the CCD dimensions, which replaces the tetrahedral volume, as well as introducing a new system optical axis.
Abstract: The full development of the equations for defocused digital particle image velocimetry as proposed by Kajitani and Dabiri (2005 Meas. Sci. Technol. 16 790–804) predefined a finite area at the focal plane to be imaged onto the CCDs. This resulted in bounded overlapping viewing cones of the lenses, i.e. the observable domain, within which a tetrahedral imaging volume was defined. The resulting ray tracing suggested that the observable domain would not be fully imaged onto the CCDs. Furthermore, the tetrahedral imaging volume, which was also a definition used to develop the characteristic three-dimensional DDPIV equations, only represented a limited portion of the observable domain. It is shown that by avoiding these incorrect definitions, a more accurate description of the three-dimensional DDPIV measurement system can be developed by introducing a new measurement volume based on the CCD dimensions, which replaces the tetrahedral volume, as well as introducing a new system optical axis. Lastly, a geometric uncertainty analysis is conducted and compared to the results found by Kajitani and Dabiri.
Patent•
14 May 2008
TL;DR: In this paper, a real-time and dynamic vector light beam generation system was proposed, in which a spatial light modulator controlled by a computer, a first lens, a wave filter, two quarter wave plates, a second lens and a Rochi grating along the light direction of the light source producing linearly polarized light.
Abstract: The invention provides a generation device of an arbitrary polarization distribution vector light beam, and is in turns provided with a spatial light modulator controlled by a computer, a first lens,a wave filter, two quarter wave plates, a second lens and a Rochi grating along the light direction of the light source producing linearly polarized light. The spatial light modulator is positioned ona front focal plane of the first lens, a back focal plane is provided with the wave filter, and the wave filter is synchronously positioned on a front focal plane of the second lens. Rochi grating ispositioned on a back focal plane of the second lens. Two quarter wave plates are placed by closely depending on the backlight source surface of the wave filter. The invention has the advantage of producing arbitrary vector light beam, and to be important, the device of the invention can produce the vector light beam in real time and dynamic manner. Moreover, the device greatly reduces the effectto the light beam quality caused by coherent noise, and can produce the high-quality vector light beam, and the producing manner is real time and dynamic.
TL;DR: In this paper, a cross-convolution method is proposed to make a test image and a reference image separately transform to match as closely as possible. But the computational efficiency is comparable with similar procedures currently in use.
Abstract: In recent years, there has been a proliferation of wide-field sky surveys to search for a variety of transient objects. Using relatively short focal lengths, the optics of these systems produce undersampled stellar images often marred by a variety of aberrations. As participants in such activities, we have developed a new algorithm for image subtraction that no longer requires high quality reference images for comparison. The computational efficiency is comparable with similar procedures currently in use. The general technique is cross-convolution: two convolution kernels are generated to make a test image and a reference image separately transform to match as closely as possible. In analogy to the optimization technique for generating smoothing splines, the inclusion of an RMS width penalty term constrains the diffusion of stellar images. In addition, by evaluating the convolution kernels on uniformly spaced subimages across the total area, these routines can accomodate point spread functions that vary considerably across the focal plane.
Patent•
[...]
20 Nov 2008
TL;DR: In this paper, a method for the laser beam machining of a workpiece is described, where a laser beam is focused by a lens, into or onto the workpiece having a boundary surface, to produce a machining effect by means of two-photon processes.
Abstract: A description is given of a method for the laser beam machining of a workpiece (2), wherein a laser beam (14) is focused by a lens (20), which has a focal plane, into or onto the workpiece (2) having a boundary surface, to produce a machining effect by means of two-photon processes, and the position of the focal point with respect to the workpiece (2) is adjusted, to obtain a reference for the position of the focal point an image of an illuminating modulation object is projected, likewise through the lens (20), onto the workpiece (2), into the focal plane or so as to intersect it, reflections of the image occurring at the boundary surface are projected into an autofocus image plane, and are detected by a camera (15), having a camera image plane, wherein the camera image plane either intersects the autofocus image plane, if the image of the illuminating modulation object lies in the focal plane, or lies in the autofocus image plane, if the image of the modulation object intersects the focal plane.
Patent•
19 Dec 2008TL;DR: An image stabilization system includes an optical assembly configured to receive electromagnetic radiation emitted by a target and produce focused image of the target; a focal plane array, the focal planes array being configured to receiving the image and integrating at least a portion of the electromagnetic radiation making up the image to produce an electrical representation of the image; sensors configured to provide kinematic data; a control system receiving the kinematics data and estimating jitter-induced motion of the images on the focal plane and outputting a control signal; and actuators configured to translate focal plane along two orthogonal axes
Abstract: An image stabilization system includes an optical assembly configured to receive electromagnetic radiation emitted by a target and produce focused image of the target; a focal plane array, the focal plane array being configured to receive the image and integrate at least a portion of the electromagnetic radiation making up the image to produce an electrical representation of the image; sensors configured to provide kinematic data; a control system receiving the kinematic data and estimating jitter-induced motion of the image on the focal plane and outputting a control signal; and actuators configured to receive the control signal and to translate the focal plane along two orthogonal axes and rotate the focal plane about a third orthogonal axis such that jitter-induced motion of the image on the focal plane is reduced.
TL;DR: In this paper, the authors describe the aberration fields for a combination of plane symmetric systems, including spherical aberration, coma, astigmatism, defocus, and distortion.
Abstract: By generalizing the wave aberration function to include plane symmetric systems, we describe the aberration fields for a combination of plane symmetric systems. The combined system aberration coefficients for the fields of spherical aberration, coma, astigmatism, defocus and distortion depend on the individual aberration coefficients and the orientations of the individual plane symmetric component systems. The aberration coefficients can be used to calculate the locations of the field nodes for the different types of aberration, including coma, astigmatism, defocus and distortion. This work provides an alternate view for combining aberrations in optical systems.
Patent•
30 Jun 2008TL;DR: In this article, a scanning wide-field telescope includes a primary reflecting mirror and a corrector assembly, which corrects light beams for spherical aberration imposed on the light beams by the primary reflector.
Abstract: A scanning wide-field telescope includes a primary reflecting mirror and a corrector assembly. The corrector assembly corrects light beams for spherical aberration imposed on the light beams by the primary reflecting mirror. The corrector assembly is located between the primary reflecting mirror and a viewing end of the telescope, and is configured to move to multiple optical focal points of the primary reflecting mirror.
TL;DR: The finite difference time domain method and the Rayleigh-Sommerfeld diffraction integrals are used and results indicate that a quite large view of field lens can be achieved by increasing the number of the holes per unit area with the mentioned structure.
Abstract: The characteristics of the phase retardations and the invariability against the incident angles are investigated when light enters the rectangular holes with different sizes perforated on metallic film. A kind of metallic structure with a great potential in imaging is brought forward. The finite difference time domain (FDTD) method and the Rayleigh-Sommerfeld diffraction integrals are used to testify the imaging ability at different incident angles by examining the electric field on focal plane. The calculation results indicate that a quite large view of field lens can be achieved by increasing the number of the holes per unit area with the mentioned structure. A metallic structured lens with a 280 µm aperture and 240 µm focal length is designed and the view angle range of ±15° can be achieved.
TL;DR: In this article, Yamamoto and Shinozaki investigated properties of 2-principal points for location mixtures of spherically symmetric distributions with focus on a linear subspace in which a set of 2 principal points must lie.
Patent•
25 Sep 2008
TL;DR: In this paper, the authors proposed a method for measuring the radiated power of an ellipse around an axis line passing through its two focal points by a predetermined angle, where the radio wave emitted from the object-to-be-measured is reflected by the wall surface and received by the reception antenna arranged at the position of the second focal point.
Abstract: A radiated power measuring method includes: a step of preparing an elliptic mirror having a closed space surrounded by a metal wall of an elliptic cylinder obtained by rotating an ellipse around an axis line passing through its two focal points by a predetermined angle; a step of placing an object-to-be-measured which can radiate a radio wave at one (first) of the focal points in such a manner that the radiation center coincides with the selected focal point; a step of arranging a reception antenna at the position of the other (second) focal point in the closed space of the elliptical mirror; and a step of emitting a radio wave from the object-to-be-measured placed at the first focal point in the closed space of the elliptical mirror so that the radio wave emitted from the object-to-be-measured is reflected by the wall surface and received by the reception antenna arranged at the position of the second focal point, thereby measuring the total radiated power emitted from the object-to-be-measured at the measurement end of the reception antenna in accordance with the output signal from the reception antenna.
TL;DR: In this article, the performance of different types of multi-layer optics for the focusing of femtosecond X-ray pulses was characterized and compared for diffraction experiments on a thin germanium film.
Abstract: We have characterized and compared the performance of different types of multi-layer optics for the focusing of femtosecond X-ray pulses. Using X-ray pulses at 8 keV, from a laser-driven plasma source we have measured the spatial distribution of the diffracted X-rays directly after and in the focal plane of the various X-ray optical devices. For a Montel optic with 7.3× magnification we obtained the largest number of focused X-ray photons per unit angle. The performance of this optic in the X-ray diffraction experiment on a thin germanium film is demonstrated.
Patent•
25 Jun 2008TL;DR: The focal plane shutter as mentioned in this paper can offer a live view function, and improve a control velocity of a shutter speed to reduce a time interval between shootings, provided that the camera is equipped with a focal plane camera.
Abstract: Provided are a focal plane shutter, which can offer a live view function, and improve a control velocity of a shutter speed to reduce a time interval between shootings, a photographing apparatus including the focal plane shutter, and a photographing method for the photographing apparatus. The focal plane shutter includes: a front curtain; a rear curtain; a support part coupled to one side of the front curtain and the rear curtain; and a movable part movably contacting one side of the support part, wherein either the front curtain or the rear curtain is independently moved by the motion of the movable part.
Patent•
9 Jan 2008
TL;DR: In this paper, a vibration mirror scanning-based selective laser micro soldering system is presented, where the system combines a high speed scanning vibration mirror and a high quality semiconductor laser or an optical-fiber laser, for realizing the energy input of the instantaneous multiple-spot welding of program control.
Abstract: The utility model provides a vibration mirror scanning - based selective laser micro soldering system and comprises a laser generator, a semireflecting mirror, a holophote, a feedback scanning system, a F-Theta mirror, a controller, a laser generator, a semireflecting mirror and a holophote, which are in optical path connection orderly; the semireflecting mirror and the holophote are in optical path connection with the relative feedback scanning system; two feedback scanning systems are in optical path connection with the workpieces through the same F-Theta mirror; the process panel of the workpieces is arranged on the focal plane of the F-Theta mirror; the laser generator and the feedback scanning system are in signal connection with the controller; the system combines a high speed scanning vibration mirror and a high quality semiconductor laser or an optical-fiber laser and a high speed switch optical gate, for realizing the energy input of the instantaneous multiple-spot welding of program control; the side of the welding spot reaches 50 - 100 micrometers; large area of micro-spot welding can be completed instantaneously in the mode of vibration mirror scanning.
TL;DR: It is shown that reconstructing individual polarization filtered images prior to calculating the Stokes parameters can reduce the error significantly and achieve spatial multiplexing within the aperture in a compact, lightweight design.
Abstract: We describe an approach to polarimetric imaging based on a unique folded imaging system with an annular aperture.
The novelty of this approach lies in the system's collection architecture, which segments the pupil plane to measure the
individual polarimetric components contributing to the Stokes vectors. Conventional approaches rely on time sequential
measurements (time-multiplexed) using a conventional imaging architecture with a reconfigurable polarization filter, or
measurements that segment the focal plane array (spatial multiplexing) by super-imposing an array of polarizers. Our
approach achieves spatial multiplexing within the aperture in a compact, lightweight design. The aperture can be
configured for sequential collection of the four polarization components required for Stokes vector calculation or in any
linear combination of those components on a common focal plane array. Errors in calculating the degree of polarization
caused by the manner in which the aperture is partitioned are analyzed, and approaches for reducing that error are
investigated. It is shown that reconstructing individual polarization filtered images prior to calculating the Stokes
parameters can reduce the error significantly.
TL;DR: In this paper, the authors present the principles of operation, the latest changes in the opto-mechanical design, and the current status of the hardware development of the LINC-NIRVANA.
Abstract: LINC-NIRVANA is the near-infrared homothetic imaging camera for the Large Binocular Telescope. Once
operational, it will provide an unprecedented combination of angular resolution, sensitivity and field of view. Its
Fringe and Flexure Tracking System (FFTS) is mandatory for an efficient interferometric operation of LINC-NIRVANA.
It is tailored to compensate low-order phase perturbations in real-time to allow for a time-stable
interference pattern in the focal plane of the science camera during the integration. Two independent control
loops are realized within FFTS: A cophasing loop continuously monitors and corrects for atmospheric and
instrumental differential piston between the two arms of the interferometer. A second loop controls common
and differential image motion resulting from changing orientations of the two optical axes of the interferometer.
Such changes are caused by flexure but also by atmospheric dispersion.
Both loops obtain their input signals from different quadrants of a NIR focal plane array. A piezo-driven
piston mirror in front of the beam combining optics serves as actuator in the cophasing loop. Differential piston
is determined by fitting a parameterized analytical model to the observed point spread function of a reference
target. Tip-tilt corrections in the flexure loop are applied via the secondary mirrors. Image motion is sensed for
each optical axis individually in out-of-focus images of the same reference target.
In this contribution we present the principles of operation, the latest changes in the opto-mechanical design,
the current status of the hardware development.