bluuebunny/crossref_metadata_2025 huggingface dataset:
Predictability of Atmospherically-distorted Stellar Wavefronts
Authors: Aitken George J. M. , McGaughey Donald
Published: February 2023

The errors caused by the inherent time delays in an adaptive-optics control loop could be overcome to a large extent by short-term prediction of the incident wavefront. Conversely, the bandwidth requirements of the loop could be relaxed. Furthermore, it is of interest to efficiently use all of the information available in the wavefront when making estimates of future values. In [1,2,3] Jorgenson and Aitken have described evidence suggesting that wavefront distortions should be treated as the output of a nonlinear dynamical system, and not simply as a filtered random process. Schwartz et al [4] have made similar suggestions.
Error reduction in centroid estimates using image intensifiers
Authors: Cagigal M. P. , Portilla M. G. , Prieto P. M.
Published: February 2023

To estimate the centroid of a light intensity distribution is a technique widely used in different fields: motion analysis of moving objects from series of frames(1); tracking systems for laser communication(2); resolution improvement by recentering short-exposures images allowing motion removing(3); and adaptive optics, when the wave-front distortion is estimated from the movement of a series of spots produced by an array of lenslet (Hartman-Shack wave-front sensor)(4).
Development of high QE, fast Avalanche Photodiodes for Astronomical Adaptive Optics
Authors: Bonaccini D. , Cova S. , Ghioni M. , Gheser R. , Zappa F.
Published: February 2023

Considering adaptive optics servosystems (AOS) in astronomical applications, a number of error sources have been identified in the wavefront sensor, which provides the reference signal of the servo-loop. These errors impair the system performance, especially with usually faint sources such as Natural Guide Stars (NGS).
Linear Spatio-Temporal Prediction for Adaptive Optics Wavefront Reconstructors
Authors: Lloyd-Hart Michael
Published: February 2023

Detailed computer simulations have been performed to evaluate the potential for spatio-temporal prediction of wavefront slope data from a Shack-Hartmann sensor to improve the imaging quality of an astronomical adaptive optics system by overcoming the effect of the inherent delay between sensing and correcting the wavefront phase error. Results of the simulations show that an improvement of a factor of at least 2 in the residual mean-square phase error can be achieved by extrapolating into the future on the basis of past wavefront measurements. Experiments will be conducted very shortly with actual data gathered at a 1.6 m telescope using a Shack-Hartmann sensor with 31-cm subapertures to test the simulations. Both the simulations and the experimental arrangement have been chosen to match closely the measured operating conditions of the adaptive optics system under construction for the 6.5 m MMT (Martin & Anderson 1995).
Comparison of Speckle Image Reconstruction Techniques: Experimental Measurements of Estimator Bias and Signal to Noise Ratio
Authors: Dayton David , Sandven Steve , Gonglewski John
Published: February 2023

Deconvolution from Wave-Front Sensing (DWFS) has been investigated both through laboratory and field experiments as a method to produce high resolution images from ground based telescopes.1,2,3 This technique has sometimes been referred to as Speclde Holography. With this technique a short exposure focal plane image is recorded simultaneously with an estimate of the atmospheric wave-front. The wave-front estimate is used to calculate an optical transfer function (OTF) for the atmosphere. This OTF estimate is then used in a deconvolution algorithm to correct the focal plane image. A synoptic sketch of a DWFS instrument is shown in figure 1.
Visibility Signal to Noise Ratio in Adaptive Optics Two-Telescope Interferometry
Authors: Conan Jean-Marc , Rousset Gérard
Published: February 2023

The study of astronomical objects requires the use of very high resolution instruments. Since it is difficult to build monolithic telescopes much larger than 10 meters in diameter, one can use long baseline interferometers1,2 that combine the optical beam of several telescopes. Each of these telescopes must be of large dimensions in order to observe very faint objects. At optical wavelengths, such instruments are therefore severely limited by the atmospheric turbulence. The telescopes must be equipped with adaptive optics (AO) systems which provide a correction of the turbulence.3-5 The work presented here is mostly extracted from Ref. [6] and gives a comparison of the signal to noise ratio (SNR) of long and short exposure visibilities in adaptive optics partial correction. It is a complement to an earlier study by G. Rousset et al.7
Artificial-Guide-Star Tilt-Anisoplanatism: Its Magnitude and (Limited) Amelioration
Authors: Fried David L.
Published: February 2023

We shall be concerned here with the problem of tilt anisoplanatism in the use of an artificial-guide-star adaptive optics system in imaging some astronomical object of interest through the turbulent atmosphere. It is well known that because the position of the back scatter region is determined by the direction in which the laser beam was transmitted an artificial-guide-star can not provide any pointing information pertaining to turbulence induced tilt— at least not in any direct manner. (Indirect methods, such as those involving second harmonic generation closely coupled with the back scatter process are being considered but the feasibility of such approaches is still unclear.) If the object of interest is sufficiently bright it can serve as the guide star for correction of turbulence induced tilt—or if there is a sufficiently bright star close enough to the object of interest then it can serve as a natural-guide-star for the correction of turbulence induced tilt. The farther away that natural-guide-star is from the object of interest the greater the discrepancy between the turbulence induced tilt for the object of interest and that for the natural-guide-star, and the lower the Strehl ratio of the image of the object of interest will be—even though the artificial-guide-star may be providing a basis for perfect adaptive optics correction of the higher-order wave front distortion.
Adaptive Astronomical Telescope with Two-Stage Wavefront Correction: current status of a project
Authors: Yeskov D. N. , Bonshtedt B. E. , Koreshev S. N. , Lebedeva G. I. , Parfenov V. A. , Podoba V. I. , Reznichenko V. V. , Seregin A. G. , Sidorov V. I. , Smirnov V. N. , Fedina L. G. , Firsov N. T. , Khakunov V. Kh. , Etsin I. SK.
Published: February 2023

At present, some large-scale programs are carried out in various countries that are aimed towards development of a new class of ground and space telescopes for both civil and military use. Being now at different stages of implementation, these programs have been initiated by both scientific and military and political causes and, to a large extent, owing to emerging technologies coupled mainly with active and adaptive optics.
All-Optical Adaptive Systems: Nonlinear Optics Approach for Phase Distortion Suppression
Authors: Vorontsov M. A.
Published: February 2023

Recent studies of nonlinear optical systems with two-dimensional (2D) feedback have led to the possibility of a new type of adaptive optical system having extremely high spatial resolution for wavefront distortion suppression - the All-Optical Adaptive (AOA) system [1-3]. Presently, dynamic phase distortion suppression is achieved through one of three basic techniques:
Review of Large Telescope Adaptive Optics Systems
Authors: Sandler David
Published: February 2023

The new generation of large telescopes begins a truly exciting new era for ground-based astronomy. By the end of the decade, nearly a dozen new telescopes with diameter D≥6.5 m will be in operation. Equipped with adaptive optics, these telescopes will provide unprecedented resolution from the ground. The rapid increase in our knowledge of the atmosphere, the refinement of adaptive optics components, and the steady increase in confidence arising from the experience of numerous groups around the world are all coming together at the right time for adaptive optics to fulfill its promise for astronomy.
W.M. Keck Observatory Adaptive Optics Facility
Authors: Wizinowich P. , Acton D. S. , Gleckler A. , Gregory T. , Stomski P. , Avicola K. , Brase J. , Friedman H. , Gavel D. , Max C.
Published: February 2023

The W.M. Keck Observatory, in collaboration with Lawrence Livermore National Laboratory (LLNL), is currently in the critical design phase of a natural guide star (NGS) and single laser guide star (LGS) adaptive optics (AO) user facility for the Nasmyth platform of the Keck II 10-m telescope.1 Two science instruments will accompany the AO facility: a near infrared camera (NIRC-2) being built at Caltech, and a near infrared spectrometer (NIRSPEC) being built at UCLA. NASA is planning to fund an interferometer between the Keck telescopes which will require a second NGS AO facility on Keck I.
First results of the CFHT Adaptive Optics Bonnette on the telescope
Authors: Rigaut Francois , Salmon Derrick , Arsenault Robin , McArthur Scot , Thomas Jim , Lai Olivier , Rouan Daniel , Gigan Pierre , Veran Jean-Pierre , Crampton David , Fletcher Murray , Stilburn Jim , Leckie Brian , Roberts Scot , Woof Robert , Boyer Corinne , Jagourel Pascal , Gaffard Jean-Paul
Published: February 2023

The CFHT adaptive optics bonnette is a general user instrument for astronomical applications. The results of the first technical and scientific runs at the telescope, not available at the summary due date, will be presented but are obviously not reported in this paper. A brief system description is given. We present the expected system performance and laboratory results.
A Solid State Raman Laser for Sodium D2 Line Resonant Excitation
Authors: Cheung E. C. , Ho J. G. , Injeyan H. , Valley M. M. , Berg J. G. , Byer R. L. , Huang Y.
Published: February 2023

A reliable, cost-effective sodium resonance source is needed for mesospheric sodium excitation in adaptive optics applications [1-2]. Previous approaches include a dye laser pumped by a green source and systems with nonlinear frequency conversion [3,4]. This paper presents a new, all solid-state source [5], which can be scaled to over 100 W in average power at 589 nm. In this approach, a 1064 nm Nd:YAG laser pumps a CaWO4Raman laser with an intra-cavity doubler (Fig. 1). Alignment of the frequency conversion system is relatively simple because the Raman process requires no phase matching, and the doubling crystal is non-critically phase matched LBO.
Design of an Infrared Camera Based Aircraft Dectection System for Laser Guide Star Installations
Authors: Friedman Herbert , Macintosh Bruce
Published: February 2023

For laser guide star installations above a few watts in average power, the irradiance of the beam exceeds the ANSI1 standards for eye safety and an aircraft detection system is required to insure that pilots or passengers are not blinded. Even for powers lower than this level, numerous incidents of temporary flash blindness have been observed2 and pose a threat to the safety of aircraft. LLNL has deployed two laser guide star systems3,4 and has obtained permits from the Federal Aviation Association which insure safe operation of these lasers. These aircraft detection systems use a combination of a rotating search radar, a narrow angle, boresight radar and visual observers to provide a triple layer of detection, each with its own access to the laser safety shutter.
Keck Adaptive Optics: User Interface and Supervisory Control Subsystem
Authors: Stomski P. , Wizinowich P. , Acton D. S. , Lupton W. , Gathright J. , Conrad A. , Lewis H. , Gregory T.
Published: February 2023

The user interface and supervisory control subsystem (UISC) of the W. M. Keck Observatory Adaptive Optics (AO) system serves three main purposes. First, it is the single point of control for the AO system, the wavefront controller subsystem, the optics bench subsystem and the laser subsystem. Second, it manages the coordination and supervision of the AO subsystems to provide a user-friendly facility with a high degree of automation. Third, it interacts with the other observatory systems as needed. The UISC is primarily a software system. The critical design of this subsystem is currently under way.
A Laser Guide Star Atmospheric Compensation System for the 3.5m Calar Alto Telescope
Authors: Caicedo Carlos , Wirth Allan , Navetta Joe , Bruno Terry
Published: February 2023

The Max Planck Institute for Astronomy in Heidelberg is constructing a laser guide star atmospheric compensation system for the 3.5m Calar Alto telescope. The system consists of a tilt compensation loop, a high-order adaptive optics loop, and a sodium wavelength dye laser. These subsystems are to be fully integrated into the observatory control software system. The hardware is to be installed at the telescope and testing begun in the Fall of 1996. This paper deals with the design of the wavefront sensing and compensation subsystem.
Laser beacon and full aperture tilt measurement
Authors: Lukin Vladimir P.
Published: February 2023

Theoretical and applied investigations into application of lasers for generation of artificial guide stars [1,2] became very popular in the last years. I think it is suitable for me to return to some results which were received 10-15 years ago and published in Soviet scientific journals. The complete summary of these results was presented in Refs. 3-8. To the broad circle of foreign researchers they become more accessible after publication of my book [9].

In that time I was involved into a problem of stabilization of a laser direction diagram. For this purpose in the focal plane of a telescope we were tracking the image of a reference beacon. In the framework of this work for a beam which passed through turbulent media and an image formed by the same optical system 1 calculated the mutual correlation of random shifts or centroids. It was assumed that the image can be the one formed by a real reference source (beacon) or by an optical beam reflected from some object.
Keck Adaptive Optics: Wavefront Control Subsystem
Authors: Brase J. , An J. , Avicola K. A. , Gavel D. , Max C. , Olivier S. , Waltjen K. , Watson J. , Wizinowich P. , Acton S. , Gleckler A. , Gregory T. , Stomski P.
Published: February 2023

Adaptive optics on the Keck 10 meter telescope will provide an unprecedented level of capability in highresolution ground-based astronomical imaging [1,2]. The system is designed to provide near diffraction limited imaging performance with Strehl > 0.3 n median Keck seeing of r0 = 25 cm, t0 = 10 msec at 500 nm wavelength. The system will be equipped with a 20 watt sodium laser guide star to provide nearly full sky coverage.
Review of laser technology and status
Authors: Fugate Robert Q.
Published: February 2023

This paper reviews the status of laser technology for the generation of artificial laser guide stars. The emphasis is on laser devices currently in use, under development, and planned. Lasers designed for resonant scattering in mesospheric sodium represent the major interest and area of greatest development. Mesospheric potassium and iron are metals of interest[1] since their wavelengths (769 and 372 nm, respectively) and nearly gaussian shaped absorption profiles are more easily reached by existing, solid-state laser materials such as Alexandrite and Ti:Sapphire. There is at least one example of lidar measurements using potassium as a mesospheric tracer[2]. Molecular oxygen and nitrogen are attractive since they are approximately 10 orders of magnitude more abundant than sodium but are problematic since conventional resonant excitation requires ultra-violet wavelengths. A few systems use or have used beacons generated by Rayleigh scattering.
Characterization of the Mesospheric Sodium Layer
Authors: Papen George C. , Gardner Chester S. , Yu Jirong
Published: February 2023

Several active adaptive optical systems using Na guide stars are currently in operation or under construction.1 Optimization of these system requires a detailed knowledge of the temporal and spatial characteristics of the Na layer on both long term (seasonal) scales and short term scales (daily and hourly). Here we present recent results on the seasonal variations of the Na layer at 40° N and on temporal and spatial variations that occur at low latitudes using data collected at the AMOS observatory at Haleakala, Maui, and onboard an NCAR research aircraft.
Prediction of Wavefront Sensor Slope Measurements Using Artificial Neural Networks
Authors: Montera Dennis A. , Welsh Byron M. , Roggemann Michael C. , Ruck Dennis W.
Published: February 2023

The resolution of ground based telescopes is limited by the random wavefront abberations caused by atmospheric turbulence. Adaptive optics systems, which compensate for atmospheric effects, have been shown to improve the resolution of these telescopes. The purpose of an adaptive optics system is to remove the atmospheric induced aberrations from an incident optical wavefront. This is accomplished by measuring the incident aberrations and removing them using a deformable mirror. Correction with a deformable mirror must take into account the effects of additive noise in the wavefront sensor, system time delays, and the possibility of a spatial separation between the object of interest and the beacon used to measure the incident wavefront. While an optimal wavefront reconstruction algorithm, such as the minimum variance reconstructor, can be derived based on statistical knowledge of the atmosphere, noise and other random effects in the adaptive optics system, the actual performance of this reconstructor may be limited by imperfect knowledge of several key parameters [1, 2, 3]. These parameters include both atmospheric and system parameters. The key atmospheric parameters include the Fried coherence length [4], r0, the

C
N
2

profile, and the wind speed profile. The key system parameter is the wavefront sensor (WFS) mean square slope measurement error. One source of wavefront reconstruction error is the system time delay. While it would be impossible to build an adaptive optical system without delay, it may be possible to predict the wavefront at the time of reconstruction based on the measured slopes. A statistical technique exists for slope measurement prediction which relies on prior knowledge of the key atmospheric and system parameters. This technique is based on knowing the covariance of the measured WFS data. Artificial neural networks, which do not require knowledge of the key parameters or the covariance statistics of the data, are compared to the statistical techniques to see if a single neural network offers the adaptability to perform well over a broad range of parameter values, without prior knowledge of the statistical parameters.
Digital Filtering Techniques and Centroid Predictors In Ao Servo-Systems
Authors: Gallieni D. , Bonaccini D.
Published: February 2023

Adaptive Optics systems need a wavefront sensor (WFS) for the servo-loop. The WFS integration time has to be selected considering SNR requirements. This requires to extend the integration period as much as possible, especially when dealing with faint sources. On the other hand, WFS sampling period imposes the discretization time-step to the entire servo-system, thus influencing its close loop bandwidth. The latter is also affected by additional time delays caused by WFS readout/reconstructor computing time.
Performance Characterization of High Performance, Low Cost Wavefront Reconstructor System
Authors: Rogers Sam , McDermott Scot
Published: February 2023

Logicon RDA has participated in the Air Force Phillips Laboratory imaging efforts under the direction of Dr. J. Gonglewski during the past years. We just finished supporting an adaptive optics experiment using a 197 actuator deformable mirror that was installed on the 3.5 m telescope located at Starfire Optical Range in Albuquerque NM. The experiment initially called for all centroid and wavefront reconstruction calculations be performed using a CSPI multiple i860 processor board. It was quickly determined that the resulting bandwidth would be insufficient to support the experiment objectives so Logicon RDA was tasked with designing and implementing a hardware based centroid and wavefront reconstructor.

A deformable mirror with a large number of actuators and a requirement for high speed control leads towards the current trend to dedicate a single processing element per actuator. While this allows flexible control with enhanced diagnostic capabilities, the size and complexity of the system increases as does the number of interfaces. Our approach, to quickly provide the needed bandwidth for this experiment, was to use a small number of inexpensive parallel processing paths that are capable of keeping up with the camera frame rate of 1000 fps. This reduced the size of our system (3, 6U VME boards) and kept the number of interfaces to a manageable number.

The centroid areas used for each actuator are completely reconfigurable (size and location) via the host processor as is the matrix used to reconstruct the wavefront. The matrix multiply is a brute force approach with no shortcuts implemented allowing the user to tailor the matrix to account for local effects if needed.

We believe that our approach is an inexpensive method to control a medium sized deformable mirror (up to 500 actuators) running at frame rates of up to 2000 fps.

We discuss the processing system configuration, the methods used to predict and measure the performance of the Deformable Mirror system, actual system performance results and show a cost breakdown and photographs of the centroid calculator and the wavefront reconstructor.
Experimental Comparison of Two Approaches for Solar Wavefront Sensing
Authors: Rimmele Thomas R. , Radick Richard R.
Published: February 2023

The Sun presents unusual problems for wavefront sensing. Unlike the nighttime sky, the Sun does not provide natural, high-contrast point sources, and creation of laser beacons bright enough to be visible against the solar disk poses major technical and operational problems. Small sunspots and pores can provide satisfactory substitutes for point sources, but these are available for only a tiny fraction of the solar disk. Wavefront sensing at arbitrary locations on the Sun requires a sensor capable of using the ubiquitous solar granulation as its target. Solar granulation is extended (its characteristic angular scale is about one arcsecond), unbounded (the angular extent of the composite granulation pattern greatly exceeds the isoplanatic angle), low contrast (a few percent), and both spatially and temporally variable (the typical evolution time scale is minutes). Conventional wavefront sensors such as shearing interferometers and simple Shack-Hartmann position sensors have difficulty dealing with targets having these characteristics, and therefore are not well-suited for general solar imaging.
Simple Neural Networks as Wavefront Slope Predictors: Training and Performance Issues
Authors: Gallant Peter J. , Aitken George J.M.
Published: February 2023

Artificial neural networks have gained significant popularity over the past several years in a wide variety of engineering applications. This popularity is due in part to the ability of a neural network that is trained using a supervised training rule such as error backpropagation to acquire a nonparametric representation of the mapping between a set of inputs and outputs without any specific knowledge of the application domain. Given a sufficient number of nonlinear terms, represented by a number of hidden-layer neurons, a multilayer neural network can model any mathematical function that is continuous and differentiable (Hecht-Nielsen, 1990). Difficulties can arise however when a network is trained with a limited amount of noisy “real” data and is then expected to operate as part of a system for a specific application. The network must acquire an internal representation, as stored in its weights, during the training phase that subsequently generalizes well to unseen data. In the case of a prediction application, generalization capability becomes the paramount design criteria. The generalization performance of a trained network is a strong function of several factors, including: the architecture and complexity of the network, the type of supervised training rule employed, and the manner in which data is preprocessed and presented to the network.
Bubbles, Disks, and Planets: Science with the University of Hawai’i AO System
Authors: Close Laird M. , Roddier Francois , Roddier Claude , Northcott Malcolm , Graves J. Elon (Buzz)
Published: February 2023

The Adaptive Optics system, built at the Institute for Astronomy (University of Hawai’i), has been making unique scientific observations since 1993. During that period this versatile AO system has been mounted at both Cassegrain and coude feeds at the 3.6m CFH telescope and the bent Cassegrain at the 3.8m UKIRT telescope. The instrument is now permanently a Cassegrain instrument which has enjoyed 24 nights of 4m class observing at Manua Kea.
Observing with adaptive optics.
Authors: Northcott. M. J.
Published: February 2023

The University of Hawaii adaptive optics (AO) group is now been using their AO system at the CFHT Cassegrain focus to make astronomical observations. Having spent large amounts of time reducing that data from these observing runs, we have developed procedures at the telescope to ensure good quality data whilst also attempting to reduce the observing overhead. While the UH AO system is a low order natural guide star system, we feel that the lessons learned from this system should be broadly relevant to most AO systems.
Halo Properties and Their Influence on Companion Searches at the Starfire Optical Range
Authors: Ryan P.T. , Angel J.R.P. , McCarthy D.W. , Close L.M. , Mohanty S. , Fugate R. , Sandler D.G.
Published: February 2023

One of the questions which has endured for as long as man has looked at the heavens is ”Are we alone?”. Are there beings on other planets who are also looking into the heavens? The first requirement for alien life similar to our own is that there be planets orbiting other stars. The early stages of planet formation as dictated by theory appear to be robust and several large planets have recently been detected by indirect means[1][2]. Direct imaging is currently being used to search for less ambitious, yet still scientifically interesting faint objects called Brown Dwarfs. The most convincing evidence of a Brown Dwarf, a cross between a star and a planet, was discovered by direct imaging with the aid of a 7.7 arcsecond separation from a companion star[3].
Post-Processing of Adaptive Optics Images: Blind Deconvolution Analysis
Authors: Christou Julian C. , Hege E. Keith , Jefferies Stuart M.
Published: February 2023

Adaptive Optics (AO) has the capability of providing diffraction-limited images from ground-based astronomical telescopes through the turbulent atmosphere. Because of limitations in the AO system, the point spread functions (PSF’s) of the AO system suffers from incomplete compensation and variability. Depending on the observation wavelength (λ), the spatial coherence length of the atmosphere (r0), the sub-aperture size (d), the correlation time of the atmosphere (τ0), the sample time of the wavefront sensing (t
s
), and the signal strength of the source, the Strehl ratios of the compensated images can vary considerably (between 2% – 90%). In addition, residual errors in tilt compensation due to the source signal strength can further degrade the image quality. Thus, AO compensated imaging genearally requires some post-processing to extract the maximum possible information. As long as the PSF for the imaging process is stationary, then standard deconvolution algorithms can be applied. These algorithms have been recently developed and applied to Hubble Space Telescope imaging and include maximum-likelihood, maximum-entropy and pixon-based algorithms, etc.[1].
Fourier phase spectrum estimation using deconvolution from wavefront sensing and bispectrum reconstruction
Authors: Roggemann Michael C. , Hyde Cynthia A. , Welsh Byron M.
Published: February 2023

Many techniques for overcoming the optical effects of turbulence have been studied. These correction techniques include post detection image processing, such as speckle imaging (SI) [1] and deconvolution from wavefront sensing (DWFS) [2]. The post detection image processing techniques of speckle imaging and DWFS are of interest because they avoid the investment in expensive and complicated hardware required for adaptive optics. A key factor distinguishing DWFS from SI is that no separate phase spectrum reconstruction step analogous to computing and processing the bispectrum is required in DWFS. We show here that for bright extended objects DWFS provides much better phase spectrum estimation than the bispectrum technique. The qualifier bright is used to describe the case where the object or beacon is bright enough to provide ample signal for low noise wave front estimation using a Hartmann sensor.
A new method for separating atmospheric layers using a Shack-Hartmann Curvature Sensor
Authors: Glindemann Andreas , Berkefeld Thomas
Published: February 2023

Using a Shack-Hartmann sensor for measuring the wavefront gradient and the wavefront curvature by integrating over the subapertures allows to separate the influence of atmospheric layers.
Variances of Optical Transfer Functions of the Turbulent Atmosphere
Authors: Lukin Igor P.
Published: February 2023

The variances of optical transfer functions of the optical system “Turbulent Atmosphere - Telescope” are investigated theoretically by two methods of posteriory processing (Labeyrie and Knox-Tompson) of the astronomical images. This characteristics are approximated the phase variances of intensity spectrum of the images.
Spatial Spikes of Intensity of the Atmospherically–distorted Images
Authors: Lukin Igor P.
Published: February 2023

At registration of astronomical objects through the turbulent atmosphere for large telescopes conditions will be usually realized, when the astronomical image represents from self a chaotic picture interleaved light and dark spots (speckle-strusture). In this connection, it is represented interesting to give an estimation of size of characteristic parameters of these areas. In given message the similar analysis will be carried out on the basis of treatment light spots of speckle-structure as the random spikes of intensity of the astronomical image.
Phase-diverse speckle restorations of artificial satellites imaged with adaptive-optics compensation
Authors: Seldin John H. , Paxman Richard G. , Ellerbroek Brent L. , Johnston Dustin C.
Published: February 2023

1. BACKGROUND

The resolution achieved in ground-based space-object imaging is usually limited by turbulence-induced aberrations. Although adaptive-optics systems designed to eliminate phase aberrations introduced by atmospheric turbulence correct a large portion of these aberrations, the correction is never perfect. There are several sources of residual aberrations that degrade the imagery: imperfect wavefront sensing (particularly in low light level situations), the time lag between sensing and correction (which allows for evolution of the atmosphere and is a particular problem when slewing to track an earth-orbiting space object), and deformable-mirror fitting errors. There are also scenarios in which adaptive-optics compensation is intermittent, degraded, or simply unavailable. For instance, when tracking an artificial satellite at a sufficiently high slew rate, the performance of the adaptive optics loop can degrade and fluctuate to a degree which severely limits the resolution in the images. Furthermore, a pure post-detection capability insures the continuing availability of fine-resolution images, even during adaptive-optics down time owing to routine maintenance or temporary system failure. Therefore, post-detection reconstruction methods provide an important complement to and backup for pre-detection correction.
CFHT Adaptive Optics & Adonis observations of Starburst galaxies
Authors: Lai O. , Rouan D. , Gendron E. , Rigaut F.
Published: February 2023

To be able to understand the link between starburst and AGN (are starburst progenitors of AGNs? e.g. Sanders et al 1988), high angular resolution is essential so as to identify each phenomena, and their respective contribution to the luminosity. Observations first carried out with ADONIS, ESO's adaptive optics instrument, and now with PUEO, CFHT's adaptive optics bonnette of starburst galaxies allow to study the morphology of potential starburst regions, and more precisely, to shed some light on the probable link between starburst activity and characteristic structures; for instance, these can be very young or old star population aggregate, circumnuclear starburst disks or rings. Signs of mergers (multiple nuclei, wisps or tails) are also of interest as they allow to look into the question whether there always is a merger at the onset of a starburst (Mirabel & Sanders, 1989), and if so, at which phase.
Intensity peak tracking in extended-object astronomical imaging
Authors: Tyler David W.
Published: February 2023

Adaptive optics are becoming more common at astronomical facilities. At sites such as Mauna Kea, near-IR seeing can be good enough that aberration power is largely confined to tip-tilt, even with larger telescopes. Accordingly, many low-order systems are being planned and studied, with simple tilt compensation schemes being used at several observatories [1,2,3] for near-IR imaging. Image motion can also be removed in post­detection processing if an ensemble of short-exposure images is collected. For either real-time or post­detection processing, proper choice of a tilt removal scheme can improve resolution in long-exposure images.
Simultaneous short exposure measurements of anisoplanatism using compensated images at optical and near infrared wavelengths
Authors: Christou Julian C. , Ellerbroek Brent L. , Pennington Timothy L. , Riker James F. , Roark J. Timothy , Spillar Earl J.
Published: February 2023

Work is in progress towards a series of observations to characterize the short- and long-exposure performance of an adaptive optics system as a function of wavelength and field-of-view. A principal goal of this effort will be to characterize the anisoplanatism observed in the infrared while using an off-axis visual guide star for tracking. More generally, we will investigate the effects of various methods for real-time and post-facto image tracking upon image quality in the presence of anisoplanatism. The instrumentation for the experiment is similar to that reported in [1], with the addition of an infrared sensor. Images are formed using the 1.5-meter telescope at the U. S. Air Fore Phillips Laboratory Starfire Optical Range and its adaptive optics system [2]. A beamsplitter sends the visible portion of the spectrum to a high speed, 64 by 64 pixel MIT/Lincoln Laboratory CCD array with high quantum efficiency and low readout noise. Re-imaging optics enable both components of wide binaries to be formed on the same array with a plate scale of 289 nrad/pixel. The infrared portion of the spectrum is imaged onto a 256 by 256 pixel NICMOS III detector with Infrared Labs electronics yielding approximately 100e- read noise. We are able to obtain simultaneous wave front sensor, optical, and infrared data with integration times of from 1 to 50 milliseconds.
COMBINED INTRACAVITY AND OUTER CAVITY ADAPTIVE CORRECTION OF ABERRATIONS IN A SOLID STATE LASER
Authors: Polejaev Vladimir I. , Koryabin Alexander V. , Shmalhausen Victor I.
Published: February 2023

Recent results of experimental investigations of the intracavity correction of the thermal aberrations (1-4) indicated that it may be possible to control parameters of the output radiation of solid state lasers with the help of an adaptive resonator, that contains one deformable mirror. This report presents the results of experimental investigations using pulsed YAG-laser with two intracavity 8-electrodes adjacent to adaptive mirrors (Fig. 1), and one similar external adaptive mirror to correct the phase profile of the output beam.
Analysis of optical propagation characteristics of the ultra-long period grating using RCWA
Authors: Lee Yong-Jae , Kim Young Hun , Park Cheon Myeong , Yang Jin-Kyu
Published: February 2023

There have been significant research and analyses on the diffraction efficiency and characteristics of spectral grating with a wavelength-scale period. However, thus far an analysis on a diffraction grating with an ultra-long pitch over several hundred times of the wavelength (>100µm) and a very deep groove over dozens of micrometers has not been performed. We analyzed the diffraction efficiency of these gratings by using the rigorous coupled-wave analysis (RCWA) method and confirmed that the RCWA analytic results correspond well to the actual experimental results on the wide-angle beam-spreading phenomenon. In addition, because a long-period grating with a deep groove results in a small diffraction angle with relatively uniform efficiency, it is possible to convert a point-like distribution to a linear distribution for a short working distance and a discrete distribution for a very long working distance. We believe that a wide-angle line laser with a long grating period can be used in various applications, such as level detectors, precision measurements, multi-point light detecting and ranging (LiDAR) light sources, and security systems.
Sagnac interferometer-type nondegenerate polarization entangled two-photon source with a Fresnel rhomb
Authors: Aizawa Naoto , Niizeki Kazuya , Sasaki Riku , Horikiri Tomoyuki
Published: February 2023

Telecommunication wavelength-entangled photon sources (EPS) are
indispensable systems for a fiber-based quantum network. We developed
a Sagnac-type spontaneous parametric down conversion system adopting a
Fresnel rhomb as a wideband and reasonable retarder. This novelty, to
the best of our knowledge, enables the generation of a highly
nondegenerate two-photon entanglement comprising the telecommunication
wavelength (1550 nm) and quantum memory wavelength
(606 nm for Pr:YSO) with only one nonlinear crystal. Quantum
state tomography was performed to evaluate the degree of entanglement,
and the fidelity with a Bell state |Φ+⟩ with a maximum of 94.4% was obtained.
Therefore, this paper shows the potential of nondegenerate EPSs that
are compatible with both telecommunication wavelength and
quantum-memory wavelength to be installed in quantum
repeater architecture.
Sidelobe suppression in structured light sheet fluorescence microscopy by the superposition of two light sheets
Authors: Han Qian , Shi Jianping , Shi Fenghua
Published: February 2023

Light sheet microscopy has emerged as a powerful technique for three-dimensional and long-term vivo imaging within neuroscience and developmental biology. A light sheet illumination with structured light fields allows a better tradeoff between the field of view and axial resolution but suffers from strong side lobes. Here, we propose a method of producing structured light sheet illumination with suppressed side lobes by applying the superposition of two light sheets. The side lobe suppression results from the destructive interference between the side lobes and constructive interference between the main lobe of the two light sheets. In the proposed method, the incident light pattern in the rear pupil plane of the illumination objective is a combination of the incident light line beams required for the generation of the two interfering light sheets. We present a fast and simple calculation method to determine the incident light pattern in the rear pupil plane. Simulation results demonstrate the effectiveness of the proposed sidelobe suppression method for double-line light sheet, four-line light sheet, as well as line Bessel sheet. In particular, an 81% decrease in the relative side lobe energy can be achieved in case of double-line light sheet with an almost nonchanging propagation length. We show a way of using combined incident light patterns to generate structured light sheets with interference-resulted side lobe suppression, which is straightforward in design and with advantages of improved imaging performance.
Three-dimensional deep regression-based light scattering imaging system for nanoscale exosome analysis
Authors: Wang Zhuo , Chen Gao , Wang Shuanglian , Su Xuantao
Published: February 2023

Exosomes are extracellular vesicles that serve as promising intrinsic nanoscale biomarkers for disease diagnosis and treatment. Nanoparticle analysis technology is widely used in the field of exosome study. However, the common particle analysis methods are usually complex, subjective, and not robust. Here, we develop a three-dimensional (3D) deep regression-based light scattering imaging system for nanoscale particle analysis. Our system solves the problem of object focusing in common methods and acquires light scattering images of label-free nanoparticles as small as 41 nm in diameter. We develop a new method for nanoparticle sizing with 3D deep regression, where the 3D time series Brownian motion data of single nanoparticles are input as a whole, and sizes are output automatically for both entangled and untangled nanoparticles. Exosomes from the normal and cancer liver cell lineage cells are observed and automatically differentiated by our system. The 3D deep regression-based light scattering imaging system is expected to be widely used in the field of nanoparticle analysis and nanomedicine.
Effect of Molecular Polarity Variation on the Features of Organic Photoanisotropic Media
Authors: Chaganava Irakli , Kilosanidze Barbara , Kakauridze George , Kobulashvili Irine
Published: February 2023

The influence of molecular factors on the properties of organic polarization-sensitive materials has been studied. A variation of components with different polarity was carried out. The discovered regularity allows flexible customization of produced materials.
Remote Sensing and Terrestrial Laser Scanning Techniques for Archaeological Site Analysis
Authors: Muhammed Qamar Qasim , Saluh Mohammed Mejbel , Al-Azawi Razi J. , Kadhim Ahmed C. , Shaker Rabeaa Mezher
Published: February 2023

In this study, various analyses using remote sensing and Terrestrial Laser Scanning (TLS) techniques carried out for the archaeological site of Al-Mustansiriya ancient school after it is recently nominated to join the world heritage list.
Random-blockage model and adaptive feedback strategy of CSI for an indoor VLC network
Authors: Gong Guiyu , Gan Chaoqin , Fang Yong , Zhu Yifan , Hu Qiuyue
Published: February 2023

This paper investigates the feedback period of channel state information (CSI) considering random blockage for an indoor visible light communication (VLC) network. First, a random-blockage model (RBM) for the indoor VLC network was built. Through the RBM, a closed expression for the dynamic blockage and self-blockage probability were obtained. Based on the statistical method and RBM, a coherence distance model (CDM) under random blockage was established. Through the CDM, the weighted coherence distance of channel gain for user equipment at any position can be obtained under a specific distribution density of blockers. Based on the CDM, an adaptive feedback strategy for CSI was proposed, thus realizing the timely feedback of CSI under random blockage. Finally, the effectiveness of the above RBM and CDM was verified via simulation. The value obtained by Monte Carlo simulation is consistent with the theoretical value obtained by the RBM. Compared with the fixed-period feedback strategy, the adaptive feedback strategy was able to achieve compromise between improving channel reliability and reducing feedback overhead. The average interrupted time ratio and the average mean square error between the recovered channel gain and the actual channel gain were significantly reduced.
Coherent dimension reduction with integrated photonic circuits exploiting tailored disorder
Authors: Wendland Daniel , Becker Marlon , Brückerhoff-Plückelmann Frank , Bente Ivonne , Busch Kurt , Risse Benjamin , Pernice Wolfram H. P.
Published: February 2023

The number of systems that are investigated for computation in the physical domain has increased substantially in the recent past. Optical and photonic systems have drawn high interest due to their potential for carrying out energy-efficient linear operations and perceived advantages in latency and general computation speed. One of the main challenges remains to scale up integrated photonic designs to integration densities required for meaningful computation, in particular for matrix-vector multiplications. To address upscaling for photonic computing, here we propose an on-chip scheme for dimension reduction of the input data using random scattering. Exploiting tailored disorder allows us to reduce the incoming dimensionality by more than an order of magnitude, which a shallow subsequent network can use to perform image recognition tasks with high accuracy.
Real-time determination of focal position during laser fabrication with double-hole masks
Authors: Cao Binh Xuan , Le Hoang Phuong , Noh Jiwhan
Published: February 2023

Recently, ultrafast laser processing becomes increasingly significant in a broad field of academic research and engineering. A poor focusing condition can lead to permanent destruction of target sample, reduction of resolution, decrease in sensitivity of optic and electronic nano-devices, and low productivity[1,2]. Therefore, a precise, flexible, and rapid focus detection system is a considerable demand for increasing the productivity as well as accuracy of laser processing. In this paper, a new system of in situ real-time exploration of focal position during laser processing with double-hole mask is presented, possessing higher accuracy, higher reproducibility, and higher speed.
Toward photodetection at 2 μm wavelength band: GeSn/Ge multiple-quantum-well photodetectors integrated on Si substrates
Authors: Lin Jun-Han , Chang Guo-En
Published: February 2023

Optical detection at 2-μm wavelength spectral range has recently attracted increasing attention for many important applications. This can be done using narrow-bandgap III-V or II-VI based semiconductor photodetectors (PDs). Here, we report on group-IV based GeSn/Ge multiple-quantum-well (MQW) photoconductive photodetectors (PDs) for optical detection at the 2μm wavelength band. By introducing Sn into the well, the direct bandgap is reduced, thereby extending the absorption edge into longer wavelengths. The optical responsivity measurements reveal that the detection of the fabricated PDs is extended beyond 2000 nm. These results demonstrate the feasibility of GeSn/Ge MQW PDs for optical detection at the 2μm wavelength band.
Room temperature lasing operation of 1.5μm GalnAsP LD on InP/Si substrate
Authors: Kallarasan Periyanayagam Gandhi , Kamada Naoki , Onuki Yuya , Uchida Kazuki , Sugiyama Hirokazu , Han Xu , Hayasaka Natsuki , Aikawa Masaki , Shimomura Kazuhiko
Published: February 2023

The monolithic integration of optical III-V Laser Diode (LD) especially InP based LD is a predominant factor in the actualization of light sources on the silicon platform. We have proposed the monolithic integration of III-V LD epitaxial layers on the wafer-bonded InP/Si substrate via MOVPE. Our unique approach is that we do the adhesion of thin film InP and Si substrate before the MOVPE growth. We have already shown the successful demonstration of GaInAsP LD on InP/Si substrate.[1-2] In this paper, we report the room temperature lasing operation of 1.5 μm GaInAsP LD on InP/Si substrate resulting in the lowest threshold current density at the room temperature.