Showing papers on "Speckle imaging published in 2021"

Twin High-Resolution, High-Speed Imagers for the Gemini Telescopes: Instrument Description and Science Verification Results

Abstract: Two new imaging instruments, `Alopeke and Zorro, were designed, built, and commissioned at the Gemini-North and Gemini-South telescopes in 2018 and 2019, respectively. Here we describe them and present the results from over a year of operation. The two identical instruments are based on the legacy of the DSSI (Differential Speckle Survey Instrument) instrument, successfully used for years at the WIYN and the Gemini telescopes in Hawaii and Chile. `Alopeke and Zorro are dual-channel imagers having both speckle (6.7$''$) and ``wide-field'' ($\sim 1$ arcminute) field-of-view options. They were built to primarily perform speckle interferometry providing diffraction-limited imagery at optical wavebands, yielding astrometric separation uncertainties of $\pm$ 0.21 mas, position angle uncertainties of $\pm$ 0.7$^{\circ}$, and photometric uncertainties of $\Delta$m $\pm$ 0.02-0.04 magnitudes (for the blue and red channels, respectively). One of their main scientific roles is the validation and characterization of exoplanets and their host stars as discovered by transit surveys such as the NASA Kepler, K2, and TESS missions. The limiting magnitude for speckle observations at Gemini can be quite faint ($r\sim$18 in good observing conditions) but typically the observed targets are brighter. The instruments can also function as conventional CCD imagers providing a 1 arc-minute field of view and allowing simultaneous two-color, high-speed time-series operation. These resident visitor instruments are remotely operable and are available for use by the community via the peer-reviewed proposal process.

Resolution limit of single-pixel speckle imaging using multimode fiber and optical phased array

Abstract: Imaging through a multimode fiber (MMF) is a promising strategy for in vivo endoscopy due to its nature of simultaneously realizing high spatial resolution and minimal invasiveness. In MMF-based speckle imaging systems, a spatial light modulator (SLM) with a large number of pixels is commonly employed to enable independent controls of all the linearly polarized (LP) modes inside the MMF. Here, instead, we show that such an SLM can be replaced by a compact optical phased array (OPA) with a much smaller number of phase shifters without causing any penalty in resolution or sensitivity. Due to the nonlinear process inherent in field-to-intensity conversion, an OPA with N phase shifters is capable of generating ∼N2 independent illumination patterns. Since the resolution limit imposed by an MMF with M LP modes per polarization is approximated as 4M, we show that only 4M phase shifters are essentially required to utilize the full spatial capacity of MMF. We can therefore enjoy the unique benefits of a low-cost, compact, and high-speed OPA that does not require thousands of phase shifters to achieve high-resolution imaging through an MMF.

Single-shot imaging through scattering media under strong ambient light interference.

Abstract: Speckle correlation imaging (SCI) has found tremendous versatility compared with other scattering imaging approaches due to its single-shot data acquisition strategy, relatively simple optical setup, and high-fidelity reconstruction performance. However, this simplicity requires SCI experiments to be performed strictly in a darkroom condition. As background noise increases, the speckle contrast rapidly decreases, making precise interpretation of the data extremely difficult. Here, we demonstrate a method by refining the speckle in the autocorrelation domain to achieve high-performance single-shot imaging. Experiment results prove that our method is adapted to estimate objects in a low signal-to-background ratio (SBR) circumstance even if the SBR is about -23dB. Laboratory and outdoor SCI experiments are performed.

Shannon entropy and degree of polarization of a speckle pattern.

Abstract: The dependence of the Shannon entropy (SE) of a speckle pattern on the degree of polarization (DoP) of the pattern is investigated both experimentally and numerically. The superposition of two uncorrelated speckle patterns with polarization diversity is utilized to control the DoP of the superposed speckle pattern, and the SE of the pattern is estimated from the determined probability density function of intensity of the pattern. The SE is observed to be increasing quadratically with the DoP of the speckle pattern. The experimental observations are supported by the numerical studies. As the change of the SE indicates a change in the randomness of the intensity distribution, the variation of the standard deviation of intensity with the DoP is also investigated. Moreover, a linear relation between the SE and the standard deviation of intensity of a speckle pattern is also established.

An Improved Large-Field Microscopic Speckle Interferometry System for Dynamic Displacement Measurement of MEMS

Abstract: The traditional microscopic speckle interferometer has limited applications in engineering due to its small field of view. In this paper, we propose a large-field microscopic speckle interferometer which embeds two doublet lens groups in the improved Mach–Zehnder optical path structure to expand its field of view. At the same time, the new system can reduce the coherent noise of reflected light in the optical path. We use this new system to measure the dynamic displacement process of the entire surface of the microchips. The experimental results show that our improved measurement system can achieve large-field, real-time and high-precision dynamic measurement of micro-electromechanical systems (MEMS).

High-resolution imaging for advances in astronomy

Abstract: Two physical phenomena, (i) diameter of the collecting area of a telescope and (ii) turbulence in the atmosphere which introduces fluctuations in the index of refraction along the light beam, limit the minimum resolvable angle at optical and infrared wavelengths. Sharpness of astronomical images thus obtained can be significantly enhanced by using a back end adaptive optics system which reduces the incoming wavefront distortion by suitably deforming a mirror in real-time, and speckle interferometry which is a post-processing technique. The Nobel prize-2020 in physics award to astronomers has recognised the efforts of using these techniques. After a short description of the black hole, this article elucidates the methodology employed to identify such an object having a mass of about 4 million solar masses.

The NASA High-Resolution Speckle Interferometric Imaging Program: Validation and Characterization of Exoplanets and Their Stellar Hosts

Abstract: Starting in 2008, NASA has provided the exoplanet community an observational program aimed at obtaining the highest resolution imaging available as part of its mission to validate and characterize exoplanets, as well as their stellar environments, in search of life in the universe. Our current program uses speckle interferometry in the optical (320-1000 nm) with new instruments on the 3.5-m WIYN and both 8-m Gemini telescopes. Starting with Kepler and K2 follow-up, we now support TESS and other space- and ground-based exoplanet related discovery and characterization projects. The im- portance of high-resolution imaging for exoplanet research comes via identification of nearby stellar companions that can dilute the transit signal and confound derived exoplanet and stellar parameters. Our observations therefore provide crucial information allowing accurate planet and stellar properties to be determined. Our community program obtains high-resolution imagery, reduces the data, and provides all final data products, without any exclusive use period, to the community via the Exoplanet Follow-Up Observation Program (ExoFOP) website maintained by the NASA Exoplanet Science Insti- tute. This paper describes the need for high-resolution imaging and gives details of the speckle imaging program, highlighting some of the major scientific discoveries made along the way.

Speckle Interferometry at SOAR in 2020

Abstract: The results of speckle interferometric observations at the 4.1 m Southern Astrophysical Research Telescope (SOAR) in 2020, as well as earlier unpublished data, are given, totaling 1735 measurements of 1288 resolved pairs and non-resolutions of 1177 targets. We resolved for the first time 59 new pairs or subsystems in known binaries, mostly among nearby dwarf stars. This work continues our long-term speckle program. Its main goal is to monitor orbital motion of close binaries, including members of high-order hierarchies and Hipparcos pairs in the solar neighborhood. We also report observations of 892 members of young moving groups and associations, where we resolved 103 new pairs.

Speckle Imaging Characterization of Radial Velocity Exoplanet Systems

Abstract: We conducted speckle imaging observations of 53 stellar systems that were members of long-term radial velocity (RV) monitoring campaigns and exhibited substantial accelerations indicative of planetary or stellar companions in wide orbits. Our observations were made with blue and red filters using the Differential Speckle Survey Instrument at Gemini-South and the NN-Explore Exoplanet Stellar Speckle Imager at the WIYN telescope. The speckle imaging identifies eight luminous companions within two arcseconds of the primary stars. In three of these systems (HD 1388, HD 87359, and HD 104304), the properties of the imaged companion are consistent with the RV measurements, suggesting that these companions may be associated with the primary and the cause of the RV variation. For all 53 stellar systems, we derive differential magnitude limits (i.e., contrast curves) from the imaging. We extend this analysis to include upper limits on companion mass in systems without imaging detections. In 25 systems, we rule out companions with mass greater than 0.2 $M_{\odot}$, suggesting that the observed RV signals are caused by late M dwarfs or substellar (potentially planetary) objects. On the other hand, the joint RV and imaging analysis almost entirely rules out planetary explanations of the RV signal for HD 19522 and suggests that the companion must have an angular separation below a few tenths of an arcsecond. This work highlights the importance of combined RV and imaging observations for characterizing the outer regions of nearby planetary systems.

Orbits and Masses of Binaries from Speckle Interferometry at SOAR

Abstract: We present results from Speckle inteferometric observations of fifteen visual binaries and one double-line spectroscopic binary, carried out with the HRCam Speckle camera of the SOAR 4.1 m telescope. These systems were observed as a part of an on-going survey to characterize the binary population in the solar vicinity, out to a distance of 250 parsec. We obtained orbital elements and mass sums for our sample of visual binaries. The orbits were computed using a Markov Chain Monte Carlo algorithm that delivers maximum likelihood estimates of the parameters, as well as posterior probability density functions that allow us to evaluate their uncertainty. Their periods cover a range from 5 yr to more than 500 yr; and their spectral types go from early A to mid M - implying total system masses from slightly more than 4 MSun down to 0.2 MSun. They are located at distances between approximately 12 and 200 pc, mostly at low Galactic latitude. For the double-line spectroscopic binary YSC8 we present the first combined astrometric/radial velocity orbit resulting from a self-consistent fit, leading to individual component masses of 0.897 +/- 0.027 MSun and 0.857 +/- 0.026 MSun; and an orbital parallax of 26.61 +/- 0.29 mas, which compares very well with the Gaia DR2 trigonometric parallax (26.55 +/- 0.27 mas). In combination with published photometry and trigonometric parallaxes, we place our objects on an H-R diagram and discuss their evolutionary status. We also present a thorough analysis of the precision and consistency of the photometry available for them.

Improved depth characterization of internal defect using the fusion of shearography and speckle interferometry

Abstract: A hybrid nondestructive testing (NDT) approach based on the fusion of shearography and digital speckle pattern interferometry (DSPI) is proposed for depth characterization of internal defect. To this end, a novel dual-sensitive speckle interferometry system is developed for both shearography and DSPI measurements. On one hand, shearography imaging results are used to identify the internal defect location, shape, and boundary qualitatively for the preparation of subsequent depth characterization. On the other hand, an improved mechanical model combined with bending theory and DSPI imaging results is built to perform the internal defect depth prediction. Finally, the hybrid NDT experiment for a thin metallic plate with an internal planar defect is conducted for feasibility validation of the proposed fusion method. The results indicate that the relative error of defect depth detection is less than 5% compared to the existing method and show that the proposed fusion method can successfully perform improved depth characterization of internal defect.

Observations with the Differential Speckle Survey Instrument. X. Preliminary Orbits of K-dwarf Binaries and Other Stars

Abstract: This paper details speckle observations of binary stars taken at the Lowell Discovery Telescope, the WIYN Telescope, and the Gemini telescopes between 2016 January and 2019 September. The observations taken at Gemini and Lowell were done with the Differential Speckle Survey Instrument (DSSI), and those done at WIYN were taken with the successor instrument to DSSI at that site, the NN-EXPLORE Exoplanet Star and Speckle Imager (NESSI). In total, we present 378 observations of 178 systems and we show that the uncertainty in the measurement precision for the combined data set is ~2 mas in separation, ~1-2 degrees in position angle depending on the separation, and $\sim$0.1 magnitudes in magnitude difference. Together with data already in the literature, these new results permit 25 visual orbits and one spectroscopic-visual orbit to be calculated for the first time. In the case of the spectroscopic-visual analysis, which is done on the trinary star HD 173093, we calculate masses with precision of better than 1% for all three stars in that system. Twenty-one of the visual orbits calculated have a K dwarf as the primary star; we add these to the known orbits of K dwarf primary stars and discuss the basic orbital properties of these stars at this stage. Although incomplete, the data that exist so far indicate that binaries with K dwarf primaries tend not to have low-eccentricity orbits at separations of one to a few tens of AU, that is, on solar-system scales.

Time varied illumination laser speckle contrast imaging.

Abstract: Laser speckle contrast imaging is a technique to determine blood flow rate with a limitation of low dynamic range. In this Letter, we introduce a varied illumination speckle contrast imaging method. It utilizes varying illumination during exposure to customize the correlation time (flow rate) to speckle contrast relation. The method can cover an order of magnitude larger range flow rate in a single exposure compared to constant illumination methods. The proposed method enables high dynamic range flow rate imaging, which is advantageous in studying larger vessels and small arteries. We demonstrate the theory by simulations and ex vivo and in vivo measurements.

Microshape Measurement Method Using Speckle Interferometry Based on Phase Analysis

Abstract: A method for the measurement of the shape of a fine structure beyond the diffraction limit based on speckle interferometry has been reported. In this paper, the mechanism for measuring the shape of the fine structure in speckle interferometry using scattered light as the illumination light is discussed. Furthermore, by analyzing the phase distribution of the scattered light from the surface of the measured object, this method can be used to measure the shapes of periodic structures and single silica microspheres beyond the diffraction limit.

Multi-wavelength, handheld laser speckle imaging for skin evaluation.

Abstract: Objective A handheld device was developed and qualified for in vivo human skin evaluation using laser speckle imaging technology. Methods Each laser speckle device prototype allows the choice of up to three different laser wavelengths in the range of 400 nm to 800 nm in total. Speckle pattern analysis gives various speckle parameters, for example, speckle contrast, speckle size, speckle modulation or fractal dimension. The developed laser speckle device prototypes were evaluated investigating three skin issues. Results We receive reproducible results from the speckle imaging device. For skin ageing, we found significant changes within three age groups. The effect of a methyl nicotinate treatment was clearly visible and quantifiable using a moorFLPI device as well as our speckle imaging device. In terms of basal cell carcinoma diagnosis, we found significant differences between normal and diseased skin, even though the number of samples was limited. Conclusion As shown with first application examples, it was possible to demonstrate the potential of the method for skin evaluation in vivo.

Speckle interferometry at the observatorio astronómico nacional. ii

Abstract: We present speckle interferometric measurements of binary stars performed during September, October and November of 2009 with the 1.5-m telescope of the Observatorio Astronomico Nacional at SPM (Mexico). We report here the results of 645 measurements of 504 pairs of stars with a primary limiting magnitude of V = 12.3. The measured angular separations range from 0 00 .144 to 5 00 .17. 396 pairs have separations of less than 1 00 . The mean error in separation is 0 00 .033 and in position angle, 0 � .9. The usual 180 � ambiguity was corrected for the majority of position angles by comparison with observations performed by other observers.

Noninvasive imaging of two isolated objects through a thin scattering medium beyond the 3D optical memory effect by speckle-based difference strategy.

Abstract: The shape of two objects hidden behind a thin scattering medium is retrieved by the presented method. One of the two objects keeps stationary, while the other one is supposed to be gradually moving, and the Euclidean distance between them is always beyond the range of the 3D optical memory effect. We capture two speckle patterns to image the two isolated objects by using a developed speckle-differential-based strategy and the traditional speckle autocorrelation technique. The feasibility of our method is demonstrated by theoretical analysis and a set of experiments.

Depth resolution in multifocus laser speckle contrast imaging.

Abstract: Laser speckle contrast imaging (LSCI) can be used to evaluate blood flow based on spatial or temporal speckle statistics, but its accuracy is undermined by out-of-focus image blur. In this Letter, we show how the fraction of dynamic versus static light scattering is dependent on focus, and describe a deconvolution strategy to correct for out-of-focus blur. With the aid of a z-splitter, which enables instantaneous multifocus imaging, we demonstrate depth-resolved LSCI that can robustly extract multi-plane structural and flow-speed information simultaneously. This method is applied to in vivo imaging of blood vessels in a mouse cortex and provides improved estimates of blood flow speed throughout a depth range of 300µm.

Seeing measurements with the Merak Hα Telescope

Abstract: The parameter-search method (PSM) established by Rengaswamy, Ravindra, and Prabhu (Solar Phys. 294, 5, 2019) for measuring the terrestrial atmospheric seeing from long-exposure solar H $\upalpha$ images is further validated – through simulations – to include the effects of i) intermediate exposure-time, exposures that are neither as small as 1 to 20 ms used in solar speckle imaging in the visible nor as long as 1 second; ii) under-sampling of the data (with respect to the telescope’s diffraction-limit), and iii) non-ideal telescope point spread function. It is then applied to a large dataset to obtain the statistics of Fried’s parameter $r_{0}$ at Merak: a cold desert in the Himalayas. The bias due to intermediate exposure is well within the error budget. Under-sampling results in an underestimation of $r_{0}$ only when the seeing-limited point spread function is sampled at a rate worse than two pixels per seeing-limit, implying that $r_{0}$ estimated in the low-resolution mode is unreliable beyond $r_{0} = 10$ cm. The non-ideal telescope point spread function tends to reduce the estimated $r_{0}$ -values significantly only when the RMS wave-front error of the aberrated pupil is worse than $\lambda/14$ . The median seeing at Merak estimated from data spanning over five months is 2.7 arcseconds.

Simulation of statistically accurate time-integrated dynamic speckle patterns in biomedical optics

Abstract: The simulation of statistically accurate time-integrated dynamic speckle patterns using a physics-based model that accounts for spatially varying sample properties is yet to be presented in biomedical optics. In this Letter, we propose a solution to this important problem based on the Karhunen–Loeve expansion of the electric field and apply our method to the formalisms of both laser speckle contrast imaging and diffuse correlation spectroscopy. We validate our technique against solutions for speckle contrast for different forms of homogeneous field and also show that our method can readily be extended to cases with spatially varying sample properties.

DBDNet for denoising in ESPI wrapped phase patterns with high density and high speckle noise

Abstract: In this paper, we propose a dilated-blocks-based deep convolution neural network, named DBDNet, for denoising in electronic speckle pattern interferometry (ESPI) wrapped phase patterns with high density and high speckle noise. In our method, the proposed dilated blocks have a specific sequence of dilation rate and a multilayer cascading fusion structure, which can better improve the effect of speckle noise reduction, especially for phase patterns with high noise and high density. Furthermore, we have built an abundant training dataset with varieties of densities and noise levels to train our network; thus, the trained model has a good generalization and can denoise ESPI wrapped phase in various circumstances. The network can get denoised results directly and does not need any pre-process or post-process. We test our method on one group of computer-simulated ESPI phase patterns and one group of experimentally obtained ESPI phase patterns. The test images have a high degree of speckle noise and different densities. We compare our method with two representative methods in the spatial domain and frequency domain, named oriented-couple partial differential equation and windowed Fourier low pass filter (LPF), and a method based on deep learning, named fast and flexible denoising convolutional neural network (FFDNet). The denoising performance is evaluated quantitatively and qualitatively. The results demonstrate that our method can reduce high speckle noise and restore the dense areas of ESPI phase patterns, and get better results than the compared methods. We also apply our method to a series of phase patterns from a dynamic measurement and get successful results.

Orbits and masses of binaries from Speckle Interferometry at SOAR

Abstract: We present results from Speckle inteferometric observations of fifteen visual binaries and one double-line spectroscopic binary, carried out with the HRCam Speckle camera of the SOAR 4.1 m telescope. These systems were observed as a part of an on-going survey to characterize the binary population in the solar vicinity, out to a distance of 250 parsec. We obtained orbital elements and mass sums for our sample of visual binaries. The orbits were computed using a Markov Chain Monte Carlo algorithm that delivers maximum likelihood estimates of the parameters, as well as posterior probability density functions that allow us to evaluate their uncertainty. Their periods cover a range from 5 yr to more than 500 yr; and their spectral types go from early A to mid M - implying total system masses from slightly more than 4 MSun down to 0.2 MSun. They are located at distances between approximately 12 and 200 pc, mostly at low Galactic latitude. For the double-line spectroscopic binary YSC8 we present the first combined astrometric/radial velocity orbit resulting from a self-consistent fit, leading to individual component masses of 0.897 +/- 0.027 MSun and 0.857 +/- 0.026 MSun; and an orbital parallax of 26.61 +/- 0.29 mas, which compares very well with the Gaia DR2 trigonometric parallax (26.55 +/- 0.27 mas). In combination with published photometry and trigonometric parallaxes, we place our objects on an H-R diagram and discuss their evolutionary status. We also present a thorough analysis of the precision and consistency of the photometry available for them.

Visualization of exhaled breath by transmission electronic speckle pattern interferometry.

Abstract: A method for visualizing the air flow from the mouths of vocalists and wind musical instruments is presented. The method is based on a modification of electronic speckle pattern interferometry that incorporates the interference of a transmitted object beam rather than the standard method using a reflected object beam. The resulting whole-field real-time images are a valuable resource for both scientific and pedagogical use.