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Showing papers on "Adaptive optics published in 2013"


Journal ArticleDOI
TL;DR: It is shown how to design an optical device that can perform any linear function or coupling between inputs and outputs, and that other linear operations, including frequency and time mappings, are possible in principle, even if very challenging in practice, thus proving there is at least one constructive design for any conceivable linear optical component.
Abstract: We show how to design an optical device that can perform any linear function or coupling between inputs and outputs. This design method is progressive, requiring no global optimization. We also show how the device can configure itself progressively, avoiding design calculations and allowing the device to stabilize itself against drifts in component properties and to continually adjust itself to changing conditions. This self-configuration operates by training with the desired pairs of orthogonal input and output functions, using sets of detectors and local feedback loops to set individual optical elements within the device, with no global feedback or multiparameter optimization required. Simple mappings, such as spatial mode conversions and polarization control, can be implemented using standard planar integrated optics. In the spirit of a universal machine, we show that other linear operations, including frequency and time mappings, as well as nonreciprocal operation, are possible in principle, even if very challenging in practice, thus proving there is at least one constructive design for any conceivable linear optical component; such a universal device can also be self-configuring. This approach is general for linear waves, and could be applied to microwaves, acoustics, and quantum mechanical superpositions. © 2013 Chinese Laser Press OCIS codes: (220.1080) Active or adaptive optics; (130.6750) Systems; (230.3120) Integrated optics devices.

283 citations


Journal ArticleDOI
TL;DR: PALM-3000 as discussed by the authors is the second-generation adaptive optics (AO) facility for the 5.1 m Hale telescope at Palomar Observatory, which is designed for high-contrast imaging and emission spectroscopy of brown dwarfs and large planetary mass bodies at near-infrared wavelengths around bright stars.
Abstract: We describe and report first results from PALM-3000, the second-generation astronomical adaptive optics (AO) facility for the 5.1 m Hale telescope at Palomar Observatory. PALM-3000 has been engineered for high-contrast imaging and emission spectroscopy of brown dwarfs and large planetary mass bodies at near-infrared wavelengths around bright stars, but also supports general natural guide star use to V ≈ 17. Using its unique 66 × 66 actuator deformable mirror, PALM-3000 has thus far demonstrated residual wavefront errors of 141 nm rms under ~1'' seeing conditions. PALM-3000 can provide phase conjugation correction over a 6."4 × 6."4 working region at λ = 2.2 μm, or full electric field (amplitude and phase) correction over approximately one-half of this field. With optimized back-end instrumentation, PALM-3000 is designed to enable 10^(–7) contrast at 1" angular separation, including post-observation speckle suppression processing. While continued optimization of the AO system is ongoing, we have already successfully commissioned five back-end instruments and begun a major exoplanet characterization survey, Project 1640.

147 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed an approach based on the Zernike phase contrast method operating in the same wavelength as the coronagraph for the measurements of the non-common path aberrations (NCPA) between the optical path seen by the visible XAO wavefront sensor and that seen by NIR coronagraph.
Abstract: Context. Several exoplanet direct-imaging instruments (VLT-SPHERE, Gemini Planet Imager, etc.) will soon be in operation, providing original data for comparative exoplanetary science to the community. To this end, exoplanet imagers use an extreme adaptive optics (XAO) system to correct the atmospheric turbulence and provide a highly corrected beam to a near-infrared (NIR) coronagraph for suppressing diffracted stellar light. The performance of the coronagraph is, however, limited by the non-common path aberrations (NCPA) due to the differential wavefront errors existing between the visible XAO sensing path and the NIR science path and leading to residual speckles that hide the faintest exoplanets in the coronagraphic image. Aims. Accurate calibration of the NCPA in exoplanet imagers is mandatory to correct the residual, quasi-static speckles remaining in the coronagraphic images after XAO correction in order to allow the observation of exoplanets that are at least 10(6) fainter than their host star. Several approaches have been developed during these past few years to reach this goal. We propose an approach based on the Zernike phase-contrast method operating in the same wavelength as the coronagraph for the measurements of the NCPA between the optical path seen by the visible XAO wavefront sensor and that seen by the NIR coronagraph. Methods. This approach uses a focal plane phase mask of size similar to lambda/D, where. and D denote the wavelength and the telescope aperture diameter, respectively, to measure the quasi-static aberrations in the upstream pupil plane by encoding them into intensity variations in the downstream pupil image. The principle of this approach as described in several classical optical textbooks is simplified by the omission of the spatial variability of the amplitude diffracted by the phase mask. We develop a more rigorous formalism, leading to highly accurate measurement of the NCPA, in a quasi-linear way during the observation. Results. With prospects of achieving subnanometric measurement accuracy with this approach for a static phase map of standard deviation 44 nm rms at lambda = 1.625 mu m (0.026 lambda),we estimate a possible reduction of the NCPA due to chromatic differential optics by a factor ranging from 3 to 10 in the presence of adaptive optics (AO) residuals compared with the expected performance of a typical current-generation system. This would allow a reduction of the level of quasi-static speckles in the detected images by a factor 10 to 100, thus correspondingly improving the capacity to observe exoplanets.

134 citations


Journal ArticleDOI
TL;DR: A sub-aperture correlation based numerical phase correction method for interferometric full field imaging systems provided the complex object field information can be extracted without the need of any adaptive optics, spatial light modulators (SLM) and additional cameras.
Abstract: This paper proposes a sub-aperture correlation based numerical phase correction method for interferometric full field imaging systems provided the complex object field information can be extracted. This method corrects for the wavefront aberration at the pupil/ Fourier transform plane without the need of any adaptive optics, spatial light modulators (SLM) and additional cameras. We show that this method does not require the knowledge of any system parameters. In the simulation study, we consider a full field swept source OCT (FF SSOCT) system to show the working principle of the algorithm. Experimental results are presented for a technical and biological sample to demonstrate the proof of the principle.

117 citations


Journal ArticleDOI
TL;DR: An approach to exploit multiple light scattering by shaping the incident wavefront in optical coherence tomography by using a digital mirror device and a coherence-gated reflectance signal as feedback is reported.
Abstract: We report on an approach to exploit multiple light scattering by shaping the incident wavefront in optical coherence tomography (OCT). Most of the reflected signal from biological tissue consists of multiply scattered light, which is regarded as noise in OCT. A digital mirror device (DMD) is utilized to shape the incident wavefront such that the maximal energy is focused at a specific depth in a highly scattering sample using a coherence-gated reflectance signal as feedback. The proof-of-concept experiment demonstrates that this approach enhances depth-selective focusing in the presence of optical inhomogeneity, and thus extends the penetration depth in spectral domain-OCT (SD-OCT).

113 citations


Journal ArticleDOI
TL;DR: PALM-3000 as discussed by the authors is the second-generation adaptive optics facility for the 5.1m Hale telescope at Palomar Observatory, which is designed for high-contrast imaging and emission spectroscopy of brown dwarfs and large planetary mass bodies at near-infrared wavelengths around bright stars.
Abstract: We describe and report first results from PALM-3000, the second-generation astronomical adaptive optics facility for the 5.1-m Hale telescope at Palomar Observatory. PALM-3000 has been engineered for high-contrast imaging and emission spectroscopy of brown dwarfs and large planetary mass bodies at near-infrared wavelengths around bright stars, but also supports general natural guide star use to V ~ 17. Using its unique 66 x 66 actuator deformable mirror, PALM-3000 has thus far demonstrated residual wavefront errors of 141 nm RMS under 1 arcsecond seeing conditions. PALM-3000 can provide phase conjugation correction over a 6.4 x 6.4 arcsecond working region at an observing wavelength of 2.2 microns, or full electric field (amplitude and phase) correction over approximately one half of this field. With optimized back-end instrumentation, PALM-3000 is designed to enable as high as 10e-7 contrast at ~1 arc second angular separation, after including post-observation speckle suppression processing. While optimization of the adaptive optics system is ongoing, we have already successfully commissioned five back-end science instruments and begun a major exoplanet characterization survey, Project 1640, with our partners at American Museum of Natural History and Jet Propulsion Laboratory.

97 citations


Reference BookDOI
26 Apr 2013

88 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that the current generation of aperture masking observations of young solar-type stars, taken carefully in excellent observing conditions, are consistent with being limited by temporal phase noise and photon noise.
Abstract: Bispectrum phase, closure phase and their generalisation to kernel-phase are all independent of pupil-plane phase errors to first-order. This property, when used with Sparse Aperture Masking (SAM) behind adaptive optics, has been used recently in high-contrast observations at or inside the formal diffraction limit of large telescopes. Finding the limitations to these techniques requires an understanding of spatial and temporal third-order phase effects, as well as effects such as time-variable dispersion when coupled with the non-zero bandwidths in real observations. In this paper, formulae describing many of these errors are developed, so that a comparison can be made to fundamental noise processes of photon- and background-noise. I show that the current generation of aperture-masking observations of young solar-type stars, taken carefully in excellent observing conditions, are consistent with being limited by temporal phase noise and photon noise. This has relevance for plans to combine pupil-remapping with spatial filtering. Finally, I describe calibration strategies for kernel-phase, including the optimised calibrator weighting as used for LkCa 15, and the restricted kernel-phase POISE technique that avoids explicit dependence on calibrators.

87 citations


Journal ArticleDOI
TL;DR: An asymmetric pupil Fourier wavefront sensing (APF-WFS) was proposed in this paper, which can improve the Strehl ratio from 50% to over 90% in just a few iterations.
Abstract: This article introduces a novel wavefront sensing approach that relies on the Fourier analysis of a single conventional direct image. In the high Strehl ratio regime, the relation between the phase measured in the Fourier plane and the wavefront errors in the pupil can be linearized, as was shown in a previous work that introduced the notion of generalized closure-phase, or kernel-phase. The technique, to be usable as presented requires two conditions to be met: (1) the wavefront errors must be kept small (of the order of one radian or less), and (2) the pupil must include some asymmetry, which can be introduced with a mask, for the problem to become solvable. Simulations show that this asymmetric pupil Fourier wavefront sensing or APF-WFS technique can improve the Strehl ratio from 50% to over 90% in just a few iterations, with excellent photon noise sensitivity properties, suggesting that on-sky close loop APF-WFS is possible with an extreme adaptive optics system.

77 citations


Journal ArticleDOI
TL;DR: An asymmetric pupil Fourier wavefront sensing (APF-WFS) was proposed in this paper, which can improve the Strehl ratio from 50 to over 90 % in just a few iterations with excellent photon noise sensitivity properties.
Abstract: This paper introduces a novel wavefront sensing approach that relies on the Fourier analysis of a single conventional direct image. In the high Strehl ratio regime, the relation between the phase measured in the Fourier plane and the wavefront errors in the pupil can be linearized, as was shown in a previous work that introduced the notion of generalized closure-phase, or kernel-phase. The technique, to be usable as presented requires two conditions to be met: (1) the wavefront errors must be kept small (of the order of one radian or less) and (2) the pupil must include some asymmetry, that can be introduced with a mask, for the problem to become solvable. Simulations show that this asymmetric pupil Fourier wavefront sensing or APF-WFS technique can improve the Strehl ratio from 50 to over 90 % in just a few iterations, with excellent photon noise sensitivity properties, suggesting that on-sky close loop APF-WFS is possible with an extreme adaptive optics system.

70 citations


Patent
11 Oct 2013
TL;DR: An adaptive optics scanning system using a beam projection module with four or more axes of motion that can project and control the position and angle of a beam of light to or from an adaptive optics element is described in this article.
Abstract: An adaptive optics scanning system using a beam projection module with four or more axes of motion that can project and control the position and angle of a beam of light to or from an adaptive optics element. The adaptive optics scanning system is compact in size, overcoming the challenges of a traditional lens and mirror based pupil relay design. The adaptive optics scanning system has little to no dispersion, chromatic aberration, and off-axis aberration for improved optical performance. The system and methods for calibrating and optimizing the system are described. A modular adaptive optics unit that scans and interfaces an adaptive optics element is described.

Journal ArticleDOI
TL;DR: This work presents angle-resolved imaging of the human retina at an axial scan rate of 1.68 MHz, and demonstrates the benefits of JA-OCT: Speckle reduction, signal increase and suppression of specular and parasitic reflections.
Abstract: Joint-aperture optical coherence tomography (JA-OCT) is an angle-resolved OCT method, in which illumination from an active channel is simultaneously probed by several passive channels. JA-OCT increases the collection efficiency and effective sensitivity of the OCT system without increasing the power on the sample. Additionally, JA-OCT provides angular scattering information about the sample in a single acquisition, so the OCT imaging speed is not reduced. Thus, JA-OCT is especially suitable for ultra high speed in-vivo imaging. JA-OCT is compared to other angle-resolved techniques, and the relation between joint aperture imaging, adaptive optics, coherent and incoherent compounding is discussed. We present angle-resolved imaging of the human retina at an axial scan rate of 1.68 MHz, and demonstrate the benefits of JA-OCT: Speckle reduction, signal increase and suppression of specular and parasitic reflections. Moreover, in the future JA-OCT may allow for the reconstruction of the full Doppler vector and tissue discrimination by analysis of the angular scattering dependence.

Journal ArticleDOI
TL;DR: In this paper, a self-coherent camera was proposed to estimate phase and amplitude aberrations upstream of a coronagraph from the speckle complex eld in the downstream focal plane.
Abstract: Context. Direct imaging of exoplanets requires very high contrast levels, which are obtained using coronagraphs. But residual quasi-static aberrations create speckles in the focal plane downstream of the coronagraph which mask the planet. This problem appears in ground-based instruments as well as in space-based telescopes. Aims. An active correction of these wavefront errors using a deformable mirror upstream of the coronagraph is mandatory, but conventional adaptive optics are limited by dierential path aberrations. Dedicated techniques have to be implemented to measure phase and amplitude errors directly in the science focal plane. Methods. First, we propose a method for estimating phase and amplitude aberrations upstream of a coronagraph from the speckle complex eld in the downstream focal plane. Then, we present the self-coherent camera, which uses the coherence of light to spatially encode the focal plane speckles and retrieve the associated complex eld. This enable us to estimate and compensate in a closed loop for the aberrations upstream of the coronagraph. We conducted numerical simulations as well as laboratory tests using a four-quadrant phase mask and a 32x32 actuator deformable mirror. Results. We demonstrated in the laboratory our capability to achieve a stable closed loop and compensate for phase and amplitude quasi-static aberrations. We determined the best-suited parameter values to implement our technique. Contrasts better than 10 6 between 2 and 12 =D and even 3:10 7 (RMS) between 7 and 11 =D were reached in the focal plane. It seems that the contrast level is mainly limited by amplitude defects created by the surface of the deformable mirror and by the dynamic of the detector. Conclusions. These results are promising for a future application to a dedicated space mission for exoplanet characterization. A number of possible improvements have been identied.

Journal ArticleDOI
TL;DR: Adapt optics characterized and corrected the on-axis and off-axis aberrations of a GRIN lens with NA 0.8 and demonstrated a rotational-transformation-based correction procedure, which enlarged the imaging area with diffraction-limited resolution with only two aberration measurements.
Abstract: Inherent aberrations of gradient index (GRIN) lenses used in fluorescence endomicroscopes deteriorate imaging performance. Using adaptive optics, we characterized and corrected the on-axis and off-axis aberrations of a GRIN lens with NA 0.8 at multiple focal planes. We demonstrated a rotational-transformation-based correction procedure, which enlarged the imaging area with diffraction-limited resolution with only two aberration measurements. 204.8 × 204.8 µm2 images of fluorescent beads and brain slices before and after AO corrections were obtained, with evident improvements in both image sharpness and brightness after AO correction. These results show great promises of applying adaptive optical two-photon fluorescence endomicroscope to three-dimensional (3D) imaging.

Journal ArticleDOI
TL;DR: A custom Fourier domain optical coherence tomography instrument for high resolution imaging of mouse retina is presented and a commercial adaptive optics system is incorporated into the sample arm of the refractive FD-OCT system to overcome aberrations in the mouse eye.
Abstract: Small animal models of retinal diseases are important to vision research, and noninvasive high resolution in vivo rodent retinal imaging is becoming an increasingly important tool used in this field. We present a custom Fourier domain optical coherence tomography (FD-OCT) instrument for high resolution imaging of mouse retina. In order to overcome aberrations in the mouse eye, we incorporated a commercial adaptive optics system into the sample arm of the refractive FD-OCT system. Additionally, a commercially available refraction canceling lens was used to reduce lower order aberrations and specular back-reflection from the cornea. Performance of the adaptive optics (AO) system for correcting residual wavefront aberration in the mice eyes is presented. Results of AO FD-OCT images of mouse retina acquired in vivo with and without AO correction are shown as well.

Journal ArticleDOI
TL;DR: In this article, an optical wireless communication system for an operation with wavelengths detectable by silicon optoelectronic integrated circuits is described, where the field of view of the laser beam is adjusted with an adaptive optical system and aligned with a micro-electro-mechanical system based mirror.
Abstract: An optical wireless communication system for an operation with wavelengths detectable by silicon optoelectronic integrated circuits is described. We use direct modulated vertical cavity surface emitting lasers as a transmitter. The field of view of the laser beam is adjusted with an adaptive optical system and aligned with a micro-electro-mechanical system based mirror for beam steering. To receive the modulated laser beam, we develop a receiver chip in 0.35 μm BiCMOS technology. The experimental system shows a 3 Gb/s wireless transmission over a distance of 7 m with a bit-error rate <;10-9 without cost intensive optical components and complex adjustment procedure.

Journal ArticleDOI
TL;DR: A novel solution based on toroidal mirrors is investigated, and derived 2( second) order analytic solutions along with commercial ray tracing predict performance benefit of toroid mirrors for ophthalmoscopic use.
Abstract: Adaptive optics (AO) ophthalmoscopes have garnered increased clinical and scientific use for imaging the microscopic retina. Unlike conventional ophthalmoscopes, however, AO systems are commonly designed with spherical mirrors that must be used off-axis. This arrangement causes astigmatism to accumulate at the retina and pupil conjugate planes, degrading AO performance. To mitigate this effect and more fully tap the benefit of AO, we investigated a novel solution based on toroidal mirrors. Derived 2nd order analytic solutions along with commercial ray tracing predict performance benefit of toroidal mirrors for ophthalmoscopic use. For the Indiana AO ophthalmoscope, a minimum of three toroids is required to achieve performance criteria for retinal image quality, beam displacement, and beam ellipticity. Measurements with fabricated toroids and retinal imaging on subjects substantiate the theoretical predictions. Comparison to off-the-plane method is also presented.

Journal ArticleDOI
TL;DR: In this article, an iterativ improvement of the instantaneous point spread functions (PSFs) extracted from each speckle frame and the simultaneous use of multiple reference stars is proposed.
Abstract: We present a method for speckle holography that is optimised for crowded fields. Its two key features are an iterativ improvement of the instantaneous Point Spread Functions (PSFs) extracted from each speckle frame and the (optional) simultaneous use of multiple reference stars. In this way, high signal-to-noise and accuracy can be achieved on the PSF for each short exposure, which results in sensitive, high-Strehl re- constructed images. We have tested our method with different instruments, on a range of targets, and from the N- to the I-band. In terms of PSF cosmetics, stability and Strehl ratio, holographic imaging can be equal, and even superior, to the capabilities of currently available Adaptive Optics (AO) systems, particularly at short near-infrared to optical wavelengths. It outperforms lucky imaging because it makes use of the entire PSF and reduces the need for frame selection, thus leading to higher Strehl and improved sensitivity. Image reconstruction a posteriori, the possibility to use multiple reference stars and the fact that these reference stars can be rather faint means that holographic imaging offers a simple way to image large, dense stellar fields near the diffraction limit of large telescopes, similar to, but much less technologically demanding than, the capabilities of a multi-conjugate adaptive optics system. The method can be used with a large range of already existing imaging instruments and can also be combined with AO imaging when the corrected PSF is unstable.

Journal ArticleDOI
TL;DR: This work investigates how backscattered laser illumination can be used as the source for direct wavefront sensing using a pinhole-filtered Shack-Hartmann wavefront sensor and finds that the sensor produces linear response to input aberrations for a given specimen.
Abstract: Adaptive optics has been used to compensate the detrimental effects of aberrations in a range of high-resolution microscopes We investigate how backscattered laser illumination can be used as the source for direct wavefront sensing using a pinhole-filtered Shack–Hartmann wavefront sensor It is found that the sensor produces linear response to input aberrations for a given specimen The gradient of this response is dependent upon experimental configuration and specimen structure Cross sensitivity between modes is also observed The double pass nature of the microscope system leads in general to lower sensitivity to odd-symmetry aberration modes The results show that there is potential for use of this type of wavefront sensing in microscopes

Journal ArticleDOI
TL;DR: In this paper, a multi-conjugate adaptive optics (MCAO) has been proposed as a possible method for correction of these spatially variant aberrations, both for simple model specimens and using real aberration data from a biological specimen.
Abstract: Adaptive optics has been implemented in a range of high-resolution microscopes in order to overcome the problems of specimen-induced aberrations. Most implementations have used a single aberration correction across the imaged field. It is known, however, that aberrations often vary across the field of view, so a single correction setting cannot compensate all aberrations. Multi-conjugate adaptive optics (MCAO) has been suggested as a possible method for correction of these spatially variant aberrations. MCAO is modelled to simulate the correction of aberrations, both for simple model specimens and using real aberration data from a biological specimen.

Journal ArticleDOI
TL;DR: In this article, a wave-front estimation method called COFFEE (for COronagraphic Focal-plane wavefront Estimation for Exoplanet detection) is proposed to estimate the differential aberrations between the wavefront sensor and the scientific camera.
Abstract: The final performance of current and future instruments dedicated to exoplanet detection and characterization (such as SPHERE on the European Very Large Telescope, GPI on Gemini North, or future instruments on Extremely Large Telescopes) is limited by uncorrected quasi-static aberrations. These aberrations create long-lived speckles in the scientific image plane, which can easily be mistaken for planets. Common adaptive optics systems require dedicated components to perform wave-front analysis. The ultimate wave-front measurement performance is thus limited by the unavoidable differential aberrations between the wavefront sensor and the scientific camera. To reach the level of detectivity required by high-contrast imaging, these differential aberrations must be estimated and compensated for. In this paper, we characterize and experimentally validate a wave-front sensing method that relies on focal-plane data. Our method, called COFFEE (for COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection), is based on a Bayesian approach, and it consists in an extension of phase diversity to high-contrast imaging. It estimates the differential aberrations using only two focal-plane coronagraphic images recorded from the scientific camera itself. In this paper, we first present a thorough characterization of COFFEE's performance by means of numerical simulations. This characterization is then compared with an experimental validation of COFFEE using an in-house adaptive optics bench and an apodized Roddier & Roddier phase mask coronagraph. An excellent match between experimental results and the theoretical study is found. Lastly, we present a preliminary validation of COFFEE's ability to compensate for the aberrations upstream of a coronagraph.

Journal ArticleDOI
TL;DR: In this paper, the temporal evolution of the quasi-static wavefront error exhibits a linear power law, which can be used to model the evolution of speckle evolution in the context of high-contrast imaging instruments.
Abstract: Context. Observing sequences have shown that the major noise source limitation in high-contrast imaging is the presence of quasi-static speckles. The timescale on which quasi-static speckles evolve is determined by various factors, mechanical or thermal deformations, among others. Aims. Understanding these time-variable instrumental speckles and, especially, their interaction with other aberrations, referred to as the pinning effect, is paramount for the search for faint stellar companions. The temporal evolution of quasi-static speckles is, for instance, required for quantifying the gain expected when using angular differential imaging (ADI) and to determining the interval on which speckle nulling techniques must be carried out.Methods. Following an early analysis of a time series of adaptively corrected, coronagraphic images obtained in a laboratory condition with the high-order test bench (HOT) at ESO Headquarters, we confirm our results with new measurements carried out with the SPHERE instrument during its final test phase in Europe. The analysis of the residual speckle pattern in both direct and differential coronagraphic images enables the characterization of the temporal stability of quasi-static speckles. Data were obtained in a thermally actively controlled environment reproducing realistic conditions encountered at the telescope.Results. The temporal evolution of the quasi-static wavefront error exhibits a linear power law, which can be used to model quasi-static speckle evolution in the context of forthcoming high-contrast imaging instruments, with implications for instrumentation (design, observing strategies, data reduction). Such a model can be used for instance to derive the timescale on which non-common path aberrations must be sensed and corrected. We found in our data that quasi-static wavefront error increases with ~0.7 A per minute.

Journal ArticleDOI
TL;DR: The Robo-AO laser adaptive optics system employs a 10-W ultraviolet laser focused at a distance of 10 km to generate a laser guide star to create an artificial reference of known shape, also known as a 'laser guide star'.
Abstract: The angular resolution of ground-based optical telescopes is limited by the degrading effects of the turbulent atmosphere. In the absence of an atmosphere, the angular resolution of a typical telescope is limited only by diffraction, i.e., the wavelength of interest, λ, divided by the size of its primary mirror's aperture, D. For example, the Hubble Space Telescope (HST), with a 2.4-m primary mirror, has an angular resolution at visible wavelengths of ~0.04 arc seconds. The atmosphere is composed of air at slightly different temperatures, and therefore different indices of refraction, constantly mixing. Light waves are bent as they pass through the inhomogeneous atmosphere. When a telescope on the ground focuses these light waves, instantaneous images appear fragmented, changing as a function of time. As a result, long-exposure images acquired using ground-based telescopes - even telescopes with four times the diameter of HST - appear blurry and have an angular resolution of roughly 0.5 to 1.5 arc seconds at best. Astronomical adaptive-optics systems compensate for the effects of atmospheric turbulence. First, the shape of the incoming non-planar wave is determined using measurements of a nearby bright star by a wavefront sensor. Next, an element in the optical system, such as a deformable mirror, is commanded to correct the shape of the incoming light wave. Additional corrections are made at a rate sufficient to keep up with the dynamically changing atmosphere through which the telescope looks, ultimately producing diffraction-limited images. The fidelity of the wavefront sensor measurement is based upon how well the incoming light is spatially and temporally sampled. Finer sampling requires brighter reference objects. While the brightest stars can serve as reference objects for imaging targets from several to tens of arc seconds away in the best conditions, most interesting astronomical targets do not have sufficiently bright stars nearby. One solution is to focus a high-power laser beam in the direction of the astronomical target to create an artificial reference of known shape, also known as a 'laser guide star'. The Robo-AO laser adaptive optics system employs a 10-W ultraviolet laser focused at a distance of 10 km to generate a laser guide star. Wavefront sensor measurements of the laser guide star drive the adaptive optics correction resulting in diffraction-limited images that have an angular resolution of ~0.1 arc seconds on a 1.5-m telescope.

Journal ArticleDOI
TL;DR: It is demonstrated that this technique can compensate for aberrations induced by trial lenses, and measurements of the point spread function before and after compensation demonstrate near diffraction limit imaging.
Abstract: We present a method for optimization of optical coherence tomography images using wavefront sensorless adaptive optics. The method consists of systematic adjustment of the coefficients of a subset of the orthogonal Zernike bases and application of the resulting shapes to a deformable mirror, while optimizing using image sharpness as a merit function. We demonstrate that this technique can compensate for aberrations induced by trial lenses. Measurements of the point spread function before and after compensation demonstrate near diffraction limit imaging.

Journal ArticleDOI
TL;DR: It is demonstrated that the experimental realization of a laser system for ground-to-satellite optical Doppler ranging at the atmospheric turbulence limit allows operation of ground to low Earth orbit satellite coherent optical links limited only by atmospheric turbulence.
Abstract: We present the experimental realization of a laser system for ground-to-satellite optical Doppler ranging at the atmospheric turbulence limit. Such a system needs to display good frequency stability (a few parts in 10−14) while allowing large and well-controlled frequency sweeps of ±12 GHz at rates exceeding 100 MHz/s. Furthermore it needs to be sufficiently compact and robust for transportation to different astronomical observation sites, where it is to be interfaced with satellite ranging telescopes. We demonstrate that our system fulfills those requirements and should therefore allow operation of ground to low Earth orbit satellite coherent optical links limited only by atmospheric turbulence.

Journal ArticleDOI
TL;DR: In this article, a wave-front estimation method called COFFEE (for COronagraphic Focal-plane wavefront Estimation for Exoplanet detection) is proposed to estimate the differential aberrations using only two focalplane coronagraphic images recorded from the scientific camera itself.
Abstract: Context. The final performance of current and future instruments dedicated to exoplanet detection and characterization (such as SPHERE on the European Very Large Telescope, GPI on Gemini North, or future instruments on Extremely Large Telescopes) is limited by uncorrected quasi-static aberrations. These aberrations create long-lived speckles in the scientific image plane, which can easily be mistaken for planets.Aims. Common adaptive optics systems require dedicated components to perform wave-front analysis. The ultimate wave-front measurement performance is thus limited by the unavoidable differential aberrations between the wave-front sensor and the scientific camera. To reach the level of detectivity required by high-contrast imaging, these differential aberrations must be estimated and compensated for. In this paper, we characterize and experimentally validate a wave-front sensing method that relies on focal-plane data.Methods. Our method, called COFFEE (for COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection), is based on a Bayesian approach, and it consists in an extension of phase diversity to high-contrast imaging. It estimates the differential aberrations using only two focal-plane coronagraphic images recorded from the scientific camera itself.Results. We first present a thorough characterization of COFFEE’s performance by means of numerical simulations. This characterization is then compared with an experimental validation of COFFEE using an in-house adaptive optics bench and an apodized Roddier & Roddier phase mask coronagraph. An excellent match between experimental results and the theoretical study is found. Lastly, we present a preliminary validation of COFFEE’s ability to compensate for the aberrations upstream of a coronagraph.

Journal ArticleDOI
TL;DR: By using a flexible printed circuit board technology, it is demonstrated experimentally that a device of 61 actuators in thermal contact with the back surface of a high-reflective mirror is able to correct the low-order aberrations of a laser beam at 1064 nm and could be used to optimize the mode matching into Fabry-Perot cavities.
Abstract: The thermally deformable mirror is a device aiming at correcting beam-wavefront distortions for applications where classical mechanical methods are precluded by noise considerations, as in advanced gravitational wave interferometric detectors. This moderately low-cost technology can be easily implemented and controlled thanks to the good reproducibility of the actuation. By using a flexible printed circuit board technology, we demonstrate experimentally that a device of 61 actuators in thermal contact with the back surface of a high-reflective mirror is able to correct the low-order aberrations of a laser beam at 1064 nm and could be used to optimize the mode matching into Fabry–Perot cavities.

Journal ArticleDOI
TL;DR: An adaptive optics scanning laser ophthalmoscope is adapted to provide optical coherence tomography (OCT) imaging and a new spectral shaping method is developed to reduce the large sidelobes in the coherence profile of the OCT imaging when a non-ideal source is used with a minimal introduction of noise.
Abstract: An adaptive optics scanning laser ophthalmoscope (AO-SLO) is adapted to provide optical coherence tomography (OCT) imaging. The AO-SLO function is unchanged. The system uses the same light source, scanning optics, and adaptive optics in both imaging modes. The result is a dual-modal system that can acquire retinal images in both en face and cross-section planes at the single cell level. A new spectral shaping method is developed to reduce the large sidelobes in the coherence profile of the OCT imaging when a non-ideal source is used with a minimal introduction of noise. The technique uses a combination of two existing digital techniques. The thickness and position of the traditionally named inner segment/outer segment junction are measured from individual photoreceptors. In-vivo images of healthy and diseased human retinas are demonstrated.


Journal ArticleDOI
TL;DR: This paper provides an overview ofForward error correction techniques for optical core and optical access networks, and highlights how coding and modulation can be best combined in optical core networks.
Abstract: Forward error correction (FEC) techniques are essential for optical core and optical access networks In optical core networks, the emphasis is on high coding gains and extremely low output bit error rates, while allowing decoder realizations to operate at a throughput of 100 Gb/s and above Optical access networks operate at 10 Gb/s or above and require low-complexity FEC codes with low power consumption Coherent optical transmission with higher order modulation formats will become mandatory to achieve the high spectral efficiencies required in next-generation core networks In this paper, we provide an overview of these requirements and techniques, and highlight how coding and modulation can be best combined in optical core networks We also present guidelines for modulation and low-complexity FEC system design for optical access networks