Showing papers on "Adaptive optics published in 2014"
TL;DR: How technologies such as deformable mirrors and spatial light modulators, which compensate for aberrations by locally controlling the wavefront of a light wave, are now improving the performance of multiphoton, confocal, widefield and super-resolution microscopes are reviewed.
Abstract: Adaptive optics is becoming a valuable tool for high resolution microscopy, providing correction for aberrations introduced by the refractive index structure of specimens. This is proving particularly promising for applications that require images from deep within biological tissue specimens. We review recent developments in adaptive microscopy, including methods and applications. A range of advances in different microscope modalities is covered and prospects for the future are discussed. Adaptive optics is used to improve image quality across a wide range of microscopy techniques. Martin Booth from the University of Oxford in the UK reviews how technologies such as deformable mirrors and spatial light modulators, which compensate for aberrations by locally controlling the wavefront of a light wave, are now improving the performance of multiphoton, confocal, widefield and super-resolution microscopes. The benefits of such improvements are especially appealing for images captured from within biological tissue (focal distances of tens to hundreds of micrometres), where low-order aberrations associated with smooth phase variations occur. One future challenge is the development of efficient measurement and correction schemes for higher-order phase variations.
522 citations
TL;DR: In this article, the authors review the development of adaptive optics as an effective tool that allows using controllable optical elements to eliminate irregular distortions that occur as light propagates in an inhomogeneous medium.
Abstract: In connection with the wide use of optoelectronic systems, we review the development of adaptive optics as an effective tool that allows using controllable optical elements to eliminate irregular distortions that occur as light propagates in an inhomogeneous medium. The subject matter of this rapidly developing field of science and technology is described. Of the ideas under development in recent years, many have been around for quite a long time, but it is only now, with the development of an up-to-date optoelectronic element base, that they have started being widely incorporated into science and engineering practice. We discuss the development of adaptive optics from mere ideas to their application in astronomy, high-power laser physics, and medicine. The current state of adaptive optics in stellar and solar astronomy is reviewed, and some results of its use in distortion correction systems of high-power laser systems and facilities are presented.
204 citations
20 Dec 2014
TL;DR: In this article, the authors demonstrate simultaneous pre-and post-turbulence compensation of multiple OAM beams, in a bidirectional free-space optical communications link, using a single adaptive optics (AO) system.
Abstract: As a recently explored property of light, orbital angular momentum (OAM) has potential in enabling multiplexing of multiple data-carrying beams, to increase the transmission capacity and spectral efficiency of a communication system. For the use of OAM multiplexing in free-space optical (FSO) communications, atmospheric turbulence presents a critical challenge. In this paper, we experimentally demonstrate simultaneous pre- and post-turbulence compensation of multiple OAM beams, in a bidirectional free-space optical communications link, using a single adaptive optics (AO) system. Each beam carries a 100 Gbit/s signal, and propagates through an emulated atmospheric turbulence. A specifically designed AO system, which utilizes a Gaussian beam for wavefront sensing and correction, is built at one end of the bidirectional link. We show that this AO system can be used to not only post-compensate the received OAM beams, but also pre-compensate the outgoing OAM beams emitted from the same link end. Experimental results show that this compensation technique helps reduce the crosstalk onto adjacent modes by more than 12 dB, achieving bit error rates below the forward error correction limit of 1×10−3, for both directions of the link. The results of work might be helpful to future implementation of OAM multiplexing, in a high-capacity FSO bidirectional link affected by atmospheric turbulence.
175 citations
TL;DR: The Gemini multiconjugate adaptive optics system (GeMS) at the Gemini South telescope in Cerro Pachon is the first sodium-based multilaser guide star (LGS) adaptive optics as discussed by the authors.
Abstract: The Gemini multiconjugate adaptive optics system (GeMS) at the Gemini South telescope in Cerro Pachon is the first sodium-based multilaser guide star (LGS) adaptive optics system. It uses five LGSs and two deformable mirrors to measure and compensate for atmospheric distortions. The GeMS project started in 1999, and saw first light in 2011. It is now in regular operation, producing images close to the diffraction limit in the near-infrared, with uniform quality over a field of view of two square arcminutes. This paper is the first one in a two-paper review of GeMS. It describes the system, explains why and how it was built, discusses the design choices and trade-offs, and presents the main issues encountered during the course of the project. Finally, we briefly present the results of the system first light.
150 citations
TL;DR: In this article, the authors used the AstraLux North instrument located at the 2.2 m telescope in the Calar Alto Observatory (Almeria, Spain) to obtain diffraction-limited images of 174 Kepler objects of interest.
Abstract: Context. The Kepler mission has discovered thousands of planet candidates. Currently, some of them have already been discarded; more than 200 have been confirmed by follow-up observations (most by radial velocity and few by other methods), and several hundreds have been validated. However, the large majority of the candidates are still awaiting for confirmation. Thus, priorities (in terms of the probability of the candidate being a real planet) must be established for subsequent radial velocity observations.Aims. The motivation of this work is to provide a set of isolated (good) host candidates to be further tested by other techniques that allow confirmation of the planet. As a complementary goal, we aim to identify close companions of the candidates that could have contaminated the light curve of the planet host due to the large pixel size of the Kepler CCD and its typical PSF of around 6 arcsec. Both goals can also provide robust statistics about the multiplicity of the Kepler hosts. Methods. We used the AstraLux North instrument located at the 2.2 m telescope in the Calar Alto Observatory (Almeria, Spain) to obtain diffraction-limited images of 174 Kepler objects of interest. A sample of demoted Kepler objects of interest (with rejected planet candidates) is used as a control for comparison of multiplicity statistics. The lucky-imaging technique used in this work is compared to other adaptive optics and speckle imaging observations of Kepler planet host candidates. To that end, we define a new parameter, the blended source confidence level (BSC), to assess the probability of an object to have blended non-detected eclipsing binaries capable of producing the detected transit.Results. We find that 67.2% of the observed Kepler hosts are isolated within our detectability limits, and 32.8% have at least one visual companion at angular separations below 6 arcsec. Indeed, we find close companions (below 3 arcsec) for the 17.2% of the sample. The planet properties of this sample of non-isolated hosts are revised according to the presence of such close companions. We report one possible S-type binary (KOI-3158), where the five planet candidates would orbit one of the components of the system. We also report three possible false positives (KOIs 1230.01, 3649.01, and 3886.01) due to the presence of close companions that modify candidate properties such that they cannot be considered as planets anymore. The BSC parameter is calculated for all the isolated targets and compared to both the value prior to any high-resolution image and, when possible, to observations from previous high-spatial resolution surveys in the Kepler sample.
149 citations
TL;DR: The Gemini Multi-conjugate Adaptive Optics System (GeMS) as mentioned in this paper is a facility instrument mounted on the Gemini South telescope, which delivers a uniform, near di↵raction limited images at near infrared wavelengths (0.95 µm - 2.5 µm) over a field of view of 120 00.
Abstract: The Gemini Multi-conjugate Adaptive Optics System - GeMS, a facility instrument mounted on the Gemini South telescope, delivers a uniform, near di↵raction limited images at near infrared wavelengths (0.95 µm - 2.5 µm) over a field of view of 120 00 . GeMS is the first sodium layer based multi laser guide star adaptive optics system used in astronomy. It uses five laser guide stars distributed on a 60 00 square constellation to measure for atmospheric distortions and two deformable mirrors to compensate for it. In this paper, the second devoted to describe the GeMS project, we present the commissioning, overall performance and operational scheme of GeMS. Performance of each sub-system is derived from the commissioning results. The typical image quality, expressed in full with half maximum, Strehl ratios and variations over the field delivered by the system are then described. A discussion of the main contributor to performance limitation is carried-out. Finally, overheads and future system upgrades are described.
132 citations
TL;DR: An adaptive optics method that modulates the intensity or phase of light rays at multiple pupil segments in parallel to determine the sample-induced aberration improved structural and functional imaging of fine neuronal processes over a large imaging volume.
Abstract: We describe an adaptive optics method that modulates the intensity or phase of light rays at multiple pupil segments in parallel to determine the sample-induced aberration. Applicable to fluorescent protein-labeled structures of arbitrary complexity, it allowed us to obtain diffraction-limited resolution in various samples in vivo. For the strongly scattering mouse brain, a single aberration correction improved structural and functional imaging of fine neuronal processes over a large imaging volume.
130 citations
TL;DR: The experimental results indicate that the correction pattern obtained from the Gaussian probe beam could be used to simultaneously compensate multiple turbulence-distorted OAM beams with different orders.
Abstract: We propose an adaptive optics compensation scheme to simultaneously compensate multiple orbital angular momentum (OAM) beams propagating through atmospheric turbulence. A Gaussian beam on one polarization is used to probe the turbulence-induced wavefront distortions and derive the correction pattern for compensating the OAM beams on the orthogonal polarization. By using this scheme, we experimentally demonstrate simultaneous compensation of multiple OAM beams, each carrying a 100 Gbit/s data channel through emulated atmospheric turbulence. The experimental results indicate that the correction pattern obtained from the Gaussian probe beam could be used to simultaneously compensate multiple turbulence-distorted OAM beams with different orders. It is found that the turbulence-induced crosstalk effects on neighboring modes are efficiently reduced by 12.5 dB, and the system power penalty is improved by 11 dB after compensation.
124 citations
TL;DR: In this article, the authors describe a procedure by which a long optical path through atmospheric turbulence can be experimentally simulated in a controlled fashion and scaled down to distances easily accessible in a laboratory setting.
Abstract: We describe a procedure by which a long () optical path through atmospheric turbulence can be experimentally simulated in a controlled fashion and scaled down to distances easily accessible in a laboratory setting. This procedure is then used to simulate a 1 km long free-space communication link in which information is encoded in orbital angular momentum spatial modes. We also demonstrate that standard adaptive optics methods can be used to mitigate many of the effects of thick atmospheric turbulence.
114 citations
TL;DR: The OOMAO toolbox as mentioned in this paper is a Matlab toolbox dedicated to Adaptive Optics (AO) systems, which is based on a small set of classes representing the source, atmosphere, telescope, wavefront sensor, Deformable Mirror (DM) and an imager of an AO system.
Abstract: Object-Oriented Matlab Adaptive Optics (OOMAO) is a Matlab toolbox dedicated to Adaptive Optics (AO) systems. OOMAO is based on a small set of classes representing the source, atmosphere, telescope, wavefront sensor, Deformable Mirror (DM) and an imager of an AO system. This simple set of classes allows simulating Natural Guide Star (NGS) and Laser Guide Star (LGS) Single Conjugate AO (SCAO) and tomography AO systems on telescopes up to the size of the Extremely Large Telescopes (ELT). The discrete phase screens that make the atmosphere model can be of infinite size, useful for modeling system performance on large time scales. OOMAO comes with its own parametric influence function model to emulate different types of DMs. The cone effect, altitude thickness and intensity profile of LGSs are also reproduced. Both modal and zonal modeling approach are implemented. OOMAO has also an extensive library of theoretical expressions to evaluate the statistical properties of turbulence wavefronts. The main design characteristics of the OOMAO toolbox are object-oriented modularity, vectorized code and transparent parallel computing. OOMAO has been used to simulate and to design the Multi-Object AO prototype Raven at the Subaru telescope and the Laser Tomography AO system of the Giant Magellan Telescope. In this paper, a Laser Tomography AO system on an ELT is simulated with OOMAO. In the first part, we set-up the class parameters and we link the instantiated objects to create the source optical path. Then we build the tomographic reconstructor and write the script for the pseudo-open-loop controller.
113 citations
TL;DR: The Robo-AO system as discussed by the authors is a fully autonomous laser adaptive optics and imaging system that routinely images over 200 objects per night with an acuity 10 times sharper at visible wavelengths than typically possible from the ground.
Abstract: As new large-scale astronomical surveys greatly increase the number of objects targeted and discoveries made, the requirement for efficient follow-up observations is crucial. Adaptive optics imaging, which compensates for the image-blurring effects of Earth's turbulent atmosphere, is essential for these surveys, but the scarcity, complexity and high demand of current systems limit their availability for following up large numbers of targets. To address this need, we have engineered and implemented Robo-AO, a fully autonomous laser adaptive optics and imaging system that routinely images over 200 objects per night with an acuity 10 times sharper at visible wavelengths than typically possible from the ground. By greatly improving the angular resolution, sensitivity, and efficiency of 1-3 m class telescopes, we have eliminated a major obstacle in the follow-up of the discoveries from current and future large astronomical surveys.
TL;DR: The first on-sky results of a Kalman filter based LQG control with vibration mitigation on the CANARY instrument at the Nasmyth platform of the 4.2-m William Herschel Telescope are presented.
Abstract: Adaptive optics provides real time correction of wavefront disturbances on ground based telescopes. Optimizing control and performance is a key issue for ever more demanding instruments on ever larger telescopes affected not only by atmospheric turbulence, but also by vibrations, windshake and tracking errors. Linear Quadratic Gaussian control achieves optimal correction when provided with a temporal model of the disturbance. We present in this paper the first on-sky results of a Kalman filter based LQG control with vibration mitigation on the CANARY instrument at the Nasmyth platform of the 4.2-m William Herschel Telescope. The results demonstrate a clear improvement of performance for full LQG compared with standard integrator control, and assess the additional improvement brought by vibration filtering with a tip-tilt model identified from on-sky data, thus validating the strategy retained on the instrument SPHERE at the VLT.
TL;DR: A new instrument that is capable of imaging human photoreceptors in three dimensions is presented, which incorporates an adaptive optics system and is equipped with a high speed axial eye tracker.
Abstract: We present a new instrument that is capable of imaging human photoreceptors in three dimensions. To achieve high lateral resolution, the system incorporates an adaptive optics system. The high axial resolution is achieved through the implementation of optical coherence tomography (OCT). The instrument records simultaneously both, scanning laser ophthalmoscope (SLO) and OCT en-face images, with a pixel to pixel correspondence. The information provided by the SLO is used to correct for transverse eye motion in post-processing. In order to correct for axial eye motion, the instrument is equipped with a high speed axial eye tracker. In vivo images of foveal cones as well as images recorded at an eccentricity from the fovea showing cones and rods are presented.
TL;DR: This work demonstrates a novel multi-camera adaptive optics (AO-)OCT system for ophthalmologic use that operates at 1 million A-lines/s at a wavelength of 790 nm with 5.3 μm axial resolution in retinal tissue and is the fastest ophthalmic OCT system in the 700 to 915 nm spectral band.
Abstract: Image acquisition speed of optical coherence tomography (OCT) remains a fundamental barrier that limits its scientific and clinical utility. Here we demonstrate a novel multi-camera adaptive optics (AO-)OCT system for ophthalmologic use that operates at 1 million A-lines/s at a wavelength of 790 nm with 5.3 μm axial resolution in retinal tissue. Central to the spectral-domain design is a novel detection channel based on four high-speed spectrometers that receive light sequentially from a 1 × 4 optical switch assembly. Absence of moving parts enables ultra-fast (50ns) and precise switching with low insertion loss (−0.18 dB per channel). This manner of control makes use of all available light in the detection channel and avoids camera dead-time, both critical for imaging at high speeds. Additional benefit in signal-to-noise accrues from the larger numerical aperture afforded by the use of AO and yields retinal images of comparable dynamic range to that of clinical OCT. We validated system performance by a series of experiments that included imaging in both model and human eyes. We demonstrated the performance of our MHz AO-OCT system to capture detailed images of individual retinal nerve fiber bundles and cone photoreceptors. This is the fastest ophthalmic OCT system we know of in the 700 to 915 nm spectral band.
TL;DR: Wavefront sensorless adaptive optics Fourier domain optical coherence tomography (FD-OCT) for in vivo small animal retinal imaging and image quality improvements with WSAO OCT are presented.
Abstract: We present wavefront sensorless adaptive optics (WSAO) Fourier domain optical coherence tomography (FD-OCT) for in vivo small animal retinal imaging. WSAO is attractive especially for mouse retinal imaging because it simplifies optical design and eliminates the need for wavefront sensing, which is difficult in the small animal eye. GPU accelerated processing of the OCT data permitted real-time extraction of image quality metrics (intensity) for arbitrarily selected retinal layers to be optimized. Modal control of a commercially available segmented deformable mirror (IrisAO Inc.) provided rapid convergence using a sequential search algorithm. Image quality improvements with WSAO OCT are presented for both pigmented and albino mouse retinal data, acquired in vivo.
TL;DR: The simulation results show that the phase distortions of OAM modes induced by turbulence can be significantly compensated by the real-time correction of the properly designed AO.
Abstract: We have evaluated the channel capacity of OAM-based FSO link under a strong atmospheric turbulence regime when adaptive optics (AO) are employed to correct the wavefront phase distortions of OAM modes. The turbulence is emulated by the Monte-Carlo phase screen method, which is validated by comparison with the theoretical phase structure function. Based on that, a closed-loop AO system with the capability of real-time correction is designed and validated. The simulation results show that the phase distortions of OAM modes induced by turbulence can be significantly compensated by the real-time correction of the properly designed AO. Furthermore, the crosstalk across channels is reduced drastically, while a substantial enhancement of channel capacity can be obtained when AO is deployed.
TL;DR: In this paper, the first on-sky demonstration of speckle nulling was achieved at the Subaru Telescope in the context of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) Project.
Abstract: This paper presents the first on-sky demonstration of speckle nulling, which was achieved at the Subaru Telescope in the context of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) Project. Despite the absence of a high-order high-bandwidth closed-loop AO system, observations conducted with SCExAO show that even in poor-to-moderate observing conditions, speckle nulling can be used to suppress static and slow speckles even in the presence of a brighter dynamic speckle halo, suggesting that more advanced high-contrast imaging algorithms developed in the laboratory can be applied to ground-based systems.
TL;DR: Robo-AO is engineered and implemented, a fully autonomous laser adaptive optics and imaging system that routinely images over 200 objects per night with an acuity 10 times sharper at visible wavelengths than typically possible from the ground.
Abstract: As new large-scale astronomical surveys greatly increase the number of objects targeted and discoveries made, the requirement for efficient follow-up observations is crucial. Adaptive optics imaging, which compensates for the image-blurring effects of Earth's turbulent atmosphere, is essential for these surveys, but the scarcity, complexity and high demand of current systems limits their availability for following up large numbers of targets. To address this need, we have engineered and implemented Robo-AO, a fully autonomous laser adaptive optics and imaging system that routinely images over 200 objects per night with an acuity 10 times sharper at visible wavelengths than typically possible from the ground. By greatly improving the angular resolution, sensitivity, and efficiency of 1-3 m class telescopes, we have eliminated a major obstacle in the follow-up of the discoveries from current and future large astronomical surveys.
TL;DR: It is shown that, when the atmospheric turbulence condition D/r0 is not larger than 1, can the coherent laser communication system works well without the correction of an AO system, and the AO technique has great potential to improve the performances of the atmospheric coherent laser communications.
Abstract: With extremely high sensitivity, the coherent laser communications has a large potential to be used in the long-range and high data-rate free space communication links. However, for the atmospheric turbulent links, the most significant factor that limits the performance of the coherent laser communications is the effect of atmospheric turbulence. In this paper, we try to integrate the adaptive optics (AO) to the coherent laser communications and analyze the performances. It is shown that, when the atmospheric turbulence condition D/r0 is not larger than 1, can the coherent laser communication system works well without the correction of an AO system. When it is in the gentle turbulent condition (around D/r0 = 2), only the tip and tilt correction can improve the mixing efficiency and the bit-error rate (BER) significantly. In the moderate (around D/r0 = 10) or relatively strong (around D/r0 = 17) turbulent condition, the AO system has to correct about 9 or 35 turbulent modes or more respectively to achieve a favorable performance. In conclusion, we have demonstrated that the AO technique has great potential to improve the performances of the atmospheric coherent laser communications.
TL;DR: In this article, the authors assess the performance and limitations of the Gemini multiconjugate adaptive optics system (GeMS) and the Gemini South Adaptive Optics Imager (GSAOI).
Abstract: The Gemini multiconjugate adaptive optics system (GeMS) is a facility instrument for the Gemini South telescope. It delivers uniform, near-diffraction-limited image quality at near-infrared wavelengths over a 2 arc min field of view. Together with the Gemini South Adaptive Optics Imager (GSAOI), a near-infrared wide-field camera, GeMS/GSAOI's combination of high spatial resolution and a large field of view will make it a premier facility for precision astrometry. Potential astrometric science cases cover a broad range of topics including exoplanets, star formation, stellar evolution, star clusters, nearby galaxies, black holes and neutron stars, and the Galactic Centre. In this paper, we assess the astrometric performance and limitations of GeMS/GSAOI. In particular, we analyse deep, mono-epoch images, multi-epoch data and distortion calibration. We find that for single-epoch, undithered data, an astrometric error below 0.2 mas can be achieved for exposure times exceeding 1 min, provided enough stars are available to remove high-order distortions. We show however that such performance is not reproducible for multi-epoch observations, and an additional systematic error of similar to 0.4 mas is evidenced. This systematic multi-epoch error is the dominant error term in the GeMS/GSAOI astrometric error budget, and it is thought to be due to time-variable distortion induced by gravity flexure.
TL;DR: The Thirty Meter Telescope (NFIRAOS) as discussed by the authors is an order 60x60 multi-conjugate adaptive optics system with two deformable mirrors, which is cooled to -30 °C to reduce thermal background.
Abstract: NFIRAOS, the Thirty Meter Telescope’s first adaptive optics system is an order 60x60 Multi-Conjugate AO system with two deformable mirrors. Although most observing will use 6 laser guide stars, it also has an NGS-only mode. Uniquely, NFIRAOS is cooled to -30 °C to reduce thermal background. NFIRAOS delivers a 2-arcminute beam to three client instruments, and relies on up to three IR WFSs in each instrument. We present recent work including: robust automated acquisition on these IR WFSs; trade-off studies for a common-size of deformable mirror; real-time computing architectures; simplified designs for high-order NGS-mode wavefront sensing; modest upgrade concepts for high-contrast imaging.
TL;DR: In this article, a customized retina tracking module was integrated into the sample arm of the 2nd-generation Indiana AO-OCT system and images were acquired on three subjects.
Abstract: Adaptive optics optical coherence tomography (AO-OCT) is a highly sensitive and noninvasive method for three dimensional imaging of the microscopic retina. Like all in vivo retinal imaging techniques, however, it suffers the effects of involuntary eye movements that occur even under normal fixation. In this study we investigated dynamic retinal tracking to measure and correct eye motion at KHz rates for AO-OCT imaging. A customized retina tracking module was integrated into the sample arm of the 2nd-generation Indiana AO-OCT system and images were acquired on three subjects. Analyses were developed based on temporal amplitude and spatial power spectra in conjunction with strip-wise registration to independently measure AO-OCT tracking performance. After optimization of the tracker parameters, the system was found to correct eye movements up to 100 Hz and reduce residual motion to 10 µm root mean square. Between session precision was 33 µm. Performance was limited by tracker-generated noise at high temporal frequencies.
TL;DR: This work consciously exploit the fundamental cause of the beam deterioration—the dispersion relation of the underlying vectorial electromagnetic modes—by their selective excitation using adaptive optics to produce output beams of high modal purity, which are well defined in three dimensions.
Abstract: The classical purpose of optical fibres is delivery of either optical power, as for welding, or temporal information, as for telecommunication. Maximum performance in both cases is provided by the use of single-mode optical fibres. However, transmitting spatial information, which necessitates higher-order modes, is difficult because their dispersion relation leads to dephasing and a deterioration of the intensity distribution with propagation distance. Here we consciously exploit the fundamental cause of the beam deterioration—the dispersion relation of the underlying vectorial electromagnetic modes—by their selective excitation using adaptive optics. This allows us to produce output beams of high modal purity, which are well defined in three dimensions. The output beam distribution is even robust against significant bending of the fibre. The utility of this approach is exemplified by the controlled rotational manipulation of live cells in a dual-beam fibre-optical trap integrated into a modular lab-on-chip system. Transmitting spatial information through optical fibres is difficult because scalar high-order modes deteriorate. Here, the authors counter deterioration using adaptive optics to excite vectorial modes, achieving high-quality beams robust against fibre bending and use those to rotate cells in a laser trap.
TL;DR: An imaging procedure that simultaneously optimizes a camera's resolution and retrieves a sample's phase over a sequence of snapshots is presented, providing an imaging system that can computationally overcome its optical imperfections to offer enhanced resolution, at the expense of taking multiple snapshots over time.
Abstract: We present an imaging procedure that simultaneously optimizes a camera’s resolution and retrieves a sample’s phase over a sequence of snapshots. The technique, termed overlapped Fourier coding (OFC), first digitally pans a small aperture across a camera’s pupil plane with a spatial light modulator. At each aperture location, a unique image is acquired. The OFC algorithm then fuses these low-resolution images into a full-resolution estimate of the complex optical field incident upon the detector. Simultaneously, the algorithm utilizes redundancies within the acquired dataset to computationally estimate and remove unknown optical aberrations and system misalignments via simulated annealing. The result is an imaging system that can computationally overcome its optical imperfections to offer enhanced resolution, at the expense of taking multiple snapshots over time.
TL;DR: The technique uses X-ray near-field speckle, generated by a scattering membrane translated using a piezo motor, to infer the deflection of X-rays from the surface, providing a nano-radian order accuracy on the mirror slopes in both the tangential and sagittal directions.
Abstract: We present a method to measure the surface profile of hard X-ray reflective optics with nanometer height accuracy and sub-millimetre lateral resolution. The technique uses X-ray near-field speckle, generated by a scattering membrane translated using a piezo motor, to infer the deflection of X-rays from the surface. The method provides a nano-radian order accuracy on the mirror slopes in both the tangential and sagittal directions. As a demonstration, a pair of focusing mirrors mounted in a Kirkpatrick-Baez (KB) configuration were characterized and the results were in good agreement with offline metrology data. It is hoped that the new technique will provide feedback to optic manufacturers to improve mirror fabrication and be useful for the online optimization of active, nano-focusing mirrors on modern synchrotron beamlines.
TL;DR: The full implementation, with real-time digital image registration, corrected the residual eye motion after optical stabilization with an accuracy of ~0.05 arcmin RMS, which to the knowledge is more accurate than any method previously reported.
Abstract: Eye motion is a major impediment to the efficient acquisition of high resolution retinal images with the adaptive optics (AO) scanning light ophthalmoscope (AOSLO). Here we demonstrate a solution to this problem by implementing both optical stabilization and digital image registration in an AOSLO. We replaced the slow scanning mirror with a two-axis tip/tilt mirror for the dual functions of slow scanning and optical stabilization. Closed-loop optical stabilization reduced the amplitude of eye-movement related-image motion by a factor of 10–15. The residual RMS error after optical stabilization alone was on the order of the size of foveal cones: ~1.66–2.56 μm or ~0.34–0.53 arcmin with typical fixational eye motion for normal observers. The full implementation, with real-time digital image registration, corrected the residual eye motion after optical stabilization with an accuracy of ~0.20–0.25 μm or ~0.04–0.05 arcmin RMS, which to our knowledge is more accurate than any method previously reported.
TL;DR: In this paper, the authors conducted a survey of nearby binary systems composed of main sequence stars of spectral types F and G in order to improve our understanding of the hierarchical nature of multiple star systems.
Abstract: We conducted a survey of nearby binary systems composed of main sequence stars of spectral types F and G in order to improve our understanding of the hierarchical nature of multiple star systems. Using Robo-AO, the first robotic adaptive optics instrument, we collected high angular resolution images with deep and well-defined detection limits in the SDSS $i'$ band. A total of 695 components belonging to 595 systems were observed. We prioritized observations of faint secondary components with separations over $10''$ to quantify the still poorly constrained frequency of their sub-systems. Of the 214 secondaries observed, 39 contain such subsystems; 19 of those were discovered with Robo-AO. The selection-corrected frequency of secondary sub-systems with periods from $10^{3.5}$ to $10^5$ days is 0.12$\pm$0.03, the same as the frequency of such companions to the primary. Half of the secondary pairs belong to quadruple systems where the primary is also a close pair, showing that the presence of sub-systems in both components of the outer binary is correlated. The relatively large abundance of 2+2 quadruple systems is a new finding, and will require more exploration of the formation mechanism of multiple star systems. We also targeted close binaries with periods less than 100~yr, searching for their distant tertiary components, and discovered 17 certain and 2 potential new triples. In a sub-sample of 241 close binaries, 71 have additional outer companions. The overall frequency of tertiary components is not enhanced, compared to all (non-binary) targets, but in the range of outer periods from $10^6$ to $10^{7.5}$ days (separations on the order of 500~AU), the frequency of tertiary components is 0.16$\pm$0.03, exceeding by almost a factor of two the frequency of similar systems among all targets (0.09).
Patent•
21 Feb 2014
TL;DR: In this article, a large dynamic range sequential wavefront sensor for vision correction or assessment procedures is described, where the wavefront beam from an eye within a large eye diopter range is made to reside within a desired physical dimension over a certain axial distance range in a wavefront image space and/or a Fourier transform space.
Abstract: Example embodiments of a large dynamic range sequential wavefront sensor for vision correction or assessment procedures are disclosed. An example embodiment optically relays a wavefront from an eye pupil or corneal plane to a wavefront sampling plane in such a manner that somewhere in the relaying process, the wavefront beam from the eye within a large eye diopter range is made to reside within a desired physical dimension over a certain axial distance range in a wavefront image space and/or a Fourier transform space. As a result, a wavefront beam shifting device can be disposed there to fully intercept and hence shift the whole beam to transversely shift the relayed wavefront.
TL;DR: In this article, the authors used a partially reflective focal plane mask to measure pointing errors for Lyot-type coronagraphs and achieved an accuracy of 10^-2 lambda/D at 638 nm for a four quadrant phase mask in the laboratory.
Abstract: High performance coronagraphic imaging of faint structures around bright stars at small angular separations requires fine control of tip, tilt and other low order aberrations. When such errors occur upstream of a coronagraph, they results in starlight leakage which reduces the dynamic range of the instrument. This issue has been previously addressed for occulting coronagraphs by sensing the starlight before or at the coronagraphic focal plane. One such solution, the coronagraphic low order wave-front sensor (CLOWFS) uses a partially reflective focal plane mask to measure pointing errors for Lyot-type coronagraphs.
To deal with pointing errors in low inner working angle phase mask coronagraphs which do not have a reflective focal plane mask, we have adapted the CLOWFS technique. This new concept relies on starlight diffracted by the focal plane phase mask being reflected by the Lyot stop towards a sensor which reliably measures low order aberrations such as tip and tilt. This reflective Lyot-based wavefront sensor is a linear reconstructor which provides high sensitivity tip-tilt error measurements with phase mask coronagraphs.
Simulations show that the measurement accuracy of pointing errors with realistic post adaptive optics residuals are approx. 10^-2 lambda/D per mode at lambda = 1.6 micron for a four quadrant phase mask. In addition, we demonstrate the open loop measurement pointing accuracy of 10^-2 lambda/D at 638 nm for a four quadrant phase mask in the laboratory.
TL;DR: The hidden structures inside a tissue phantom that could not be seen in conventional OCT are clearly revealed through the proposed system, which will boost wide-spread use of OCT for in-vivo tissue diagnosis.
Abstract: We report the enhancement in the obtained signal and penetration depth of 2-D depth-resolved images that were taken by shaping the incident wavefront in optical coherence tomography (OCT). Limitations in the penetration depth and signal to noise ratio (SNR) in OCT are mainly due to multiple scattering, which have been effectively suppressed by controlling the incident wavefront using a digital mirror device (DMD) in combination with spectral-domain OCT. The successful enhancements in the penetration depth and SNR are demonstrated in a wide-range of tissue phantoms, reaching depth enhancement of up to 92%. The hidden structures inside a tissue phantom that could not be seen in conventional OCT are clearly revealed through our proposed system. Its 2-D imaging capability, assisted by further optimization of the system for real-time acquisition speed will boost wide-spread use of OCT for in-vivo tissue diagnosis.