KEYWORDS: Cameras, Long wavelength infrared, Signal to noise ratio, Prototyping, Super resolution, Modulation transfer functions, Infrared cameras, Image processing, Imaging systems, Infrared imaging
To address the complex structure and bulky volume problem of long-wave infrared detection system, we design a front-and-back-splitting distributed long-wave infrared array camera based on fiber image bundle with a simple and high-flexibility structure. The proposed system achieves higher signal-to-noise ratio and improved resolution using image algorithm processing. Benefited by the fiber bundle, the front and back lens groups are separated, which is conductive to scanning imaging and conformal design. A principal prototype of 2-way synthesis is built to verify the imaging performance of the array camera. The prototype is used to obtain two-aperture time series images of small target. One is used as a benchmark and the other is registered and synthesized. The signal-to-noise ratio of composite image increased by 25.15% by eliminating time noise. Besides, this paper uses the redundant information among multiple micro-displacement images obtained by pixel-level displacement of fiber bundle to achieve super-resolution image reconstruction. The image resolution at least doubles in one-dimensional direction and the reconstruction algorithm can be extended to two dimensions. Experimental results of the prototype show that the distributed array camera we designed can improve the signal-to-noise ratio and realize image super-resolution reconstruction with structure simplified and volume reduced.
Infrared camera arrays have previously demonstrated the potential for long-range detection due to their distributed aperture structures, but their performance is affected by the calibration procedure. The widely used calibration method based on image registration estimates the transformation matrix between different cameras by extracting matching features, and its accuracy is limited by low-resolution infrared images. To solve this problem, a new calibration method based on infinite scene registration is developed, which has high registration accuracy and is easy to implement. The results of the laboratory experiment demonstrate that the signal-to-noise ratio of the point target is improved by 1.86 with the proposed method, which proves the effectiveness and competitiveness of the proposed method. Finally, the measured data of long-range aircraft further verifies the feasibility of the proposed method.
Based on photonic integrated circuit (PIC) technology and synthetic aperture technology, the advanced technology of segmented planar imaging, which can be used to realize ultrathin and high-resolution imaging, is proposed. We develop a sampling lens array structure that combines coherent detection and traditional imaging; it can improve the sampling of low- and medium-frequency information. Based on the proposed lens array structure, a full-chain simulation model of the segmented planar imaging system is established. Under the premise of similar imaging quality, compared with the existing sampling lens structures, the proposed lens array has a simpler structure, lower processing difficulty, and lower cost. The simulation analyses of the duty ratio of the lens array, the light splitting number of PIC arrayed waveguide gratings, and the radius of the single lens are carried out. The simulation results provide a certain reference value for the optimal design of the segmented planar optical imaging system and further prove the advantages of the proposed structure.
The fiber bundle (FB) optical system is widely used in many fields, such as medical imaging and military reconnaissance, owing to its advantages of high design freedom, small volume, and light weight. The traditional theory for the optical transfer function is not suitable for such a discrete sampling optical system. Researchers have developed numerical calculation methods to analyze the imaging quality of the discrete sampling optical system, in which the geometric model needs to be established and the coupling region needs to be determined. We have developed a simple and computationally efficient imaging theory that is suitable for various combinations of FB and CCD detectors. The coupling modulation transfer function (coupling-MTF) of discrete sampling optical systems of square-arrangement fiber bundles (SFBs) and hexagonal-arrangement fiber bundles (HFBs) are analyzed. Simulation results demonstrate that although SFB has a higher coupling-MTF than HFB, the latter is more convenient in coupling alignment operation. Our results have proven the effectiveness and universality of the proposed theory, and it can be used to guide the system design.
Due to the instability of motor speeds, asynchrony in trigger systems, and mechanical factors, the use of continuous dual-rotating compensator (DRC)-Mueller matrix ellipsometer (MME) is limited. And the stepping one is more often used on an extremely wide spectrum measuring range. However, its long measuring time limits its use. To solve this problem, we propose a weighed factor to judge the stability and robustness of this ellipsometer. This factor describes the performance of ellipsometers better than the condition number. We use this factor as the merit function to optimize the configuration of a 16-point measurement system with an improved genetic algorithm (IGA). Repeated measurement experiments on SiO2 films revealed that the optimal configuration considerably increased the measurement speed, without a notable decrease in measurement precision. The findings are not only aimed at the optimization of stepping DRC-MMEs; the IGA can also be used for other multiparameter optimization issues, and the weighed factor can be applied for the parameter optimization of other MMEs.
Laser guide stars (LGSs) increase the sky coverage of astronomical adaptive optics systems. But spot array obtained by Shack-Hartmann wave front sensors (WFSs) turns extended and elongated, due to the thickness and size limitation of sodium LGS, which affects the accuracy of the wave front reconstruction algorithm. In this paper, we compared three different centroiding algorithms , the Center-of-Gravity (CoG), weighted CoG (WCoG) and Intensity Weighted Centroid (IWC), as well as those accuracies for various extended and elongated spots. In addition, we compared the reconstructed image data from those three algorithms with theoretical results, and proved that WCoG and IWC are the best wave front reconstruction algorithms for extended and elongated spot among all the algorithms.
Pyramid wavefront sensor is a promising sensor technology based on the beam splitting in the focal plane. Due to its advantages of adjustable gain and variable spatial sampling, the pyramid wavefront sensor has been successfully applied in many large telescopes. In recent years, we have carried out the related research of this sensor. Firstly we studied the adaptive optical closed-loop system based on the liquid crystal spatial light modulator and the pyramid wavefront sensor. Subsequently, the adaptive optical system based on the pyramid wavefront sensor and the deformable mirror is studied in our lab. Currently the experiment on the 1.8-m telescope at Yunnan observatory has been successfully carried out and the high resolution images of the natural stellar star have been obtained. The experiment results are present in this paper.
During 2014-2016, the Laser guide star (LGS) adaptive optics (AO) system observation campaign has been carried out on Lijiang 1.8 meter telescope. During the campaign, two generation LGS AO systems have been developed and installed. In 2014, a long-pulsed solid Sodium prototype laser with 20W@400Hz, a beam transfer optical (BTO) system, and a laser launch telescope (LLT) with 300mm diameter were mounted onto the telescope and moved with telescope azimuth journal. At the same time, a 37-elements compact LGS AO system had been mounted on the Bent-Cassegrain focus and got its first light on observing HIP43963 (mV= 8.18mv) and reached Sr=0.27 in J Band after LGS AO compensation. In 2016, the solid Sodium laser has been upgrade to stable 32W@800Hz while D2a plus D2b repumping is used to increase the photon return, and a totally new LGS AO system with 164-elements Deformable Mirror, Linux Real Time Controller, inner closed loop Tip/tilt mirror, Multiple-PMT tracking detector is established and installed on the telescope. And the throughput for the BTO/LLT is improved nearly 20%. The campaign process, the performance of the two LGS AO systems especially the latter one, the characteristics of the BTO/LLT system and the result are present in this paper.
The Laser Guide Star Facility (LGSF) is responsible for generating the artificial laser guide stars required by the TMT Laser Guide Star (LGS) AO systems. The LGSF uses multiple sodium lasers to generate and project several LGS asterisms from a laser launch telescope located behind the TMT secondary mirror. The LGSF includes 3 main subsystems: (1) the laser system, (2) the beam transfer optics (BTO) system, (3) the associated laser safety system. At present, the LGSF is in the preliminary design phase. During this phase, the laser launch telescope trade study, Beam transfer optical path trade study are compared carefully, and some critical components prototypes have been carried out to verify the requirements, such as the polarization status control and test, the Fast Steer Mirror (FSM) prototype test.
The AO progresses for astronomy in the Key Laboratory of Adaptive Optics, Chinese Academy of Sciences are reported in this presentation. For night-time astronomical observations, the recent AO technological developments, such as Laser Guide Star, Pyramid Sensor and Deformable Secondary Mirror, are introduced. The solar AO researches are also presented for day-time astronomical observations. Furthermore, we will show the on-sky high resolution observational results in the 1.8m telescope at Gaomeigu site, Yunnan Observatory and the 1-m New Vacuum Solar Telescope (NVST) at Fuxian Lake Solar Observatory respectively.
An adaptive optics system (AOS), which consists of a 73-element piezoelectric deformable secondary mirror (DSM), a 9x9 Shack-Hartmann wavefront sensor and a real time controller has been integrated on the 1.8m telescope at the Gaomeigu site of Yunnan Astronomical Observatory, Chinese Academy of Sciences. Compared to the traditional AOS on Coude focus, the DSM AOS adopts much less reflections and consequently restrains the thermal noise and increases the energy transmitting to the system. Before the first on-sky test, this system has been demonstrated in the laboratory by compensating the simulated atmospheric turbulence generated by a rotating phase screen. A new multichannel-modulation calibration method which is used to measure the DSM based AOS interaction matrix is proposed. After integration on the 1.8m telescope, the closed-loop compensation of the atmospheric turbulence with the DSM based AOS is achieved, and the first light results from the on-sky experiment are reported.
Sodium laser guide star is an ideal source for astronomical adaptive optics system correcting wave-front aberration caused by atmospheric turbulence. However, the cost and difficulties to manufacture a compact high quality sodium laser with power higher than 20W is not a guarantee that the laser will provide a bright enough laser guide star due to the physics of sodium atom in the atmosphere. It would be helpful if a prediction tool could provide the estimation of photon generating performance for arbitrary laser output formats, before an actual laser were designed. Based on rate equation, we developed a Monte Carlo simulation software that could be used to predict sodium laser guide star generating performance for arbitrary laser formats. In this paper, we will describe the model of our simulation, its implementation and present comparison results with field test data.
A 3mm narrow interval deformable mirror (DM) with tip-tilt stage has been developed for astronomical instruments.
Benefiting from its compact design, the adaptive optics system can be built with simple structure and smaller optical
elements. First, a 37-elements prototype mirror has been developed for our 1.8-meter telescope, which interval space is
3mm, maximum tilt is ±10’, and maximum deformation is ±2μm. Based on this mirror, a simple adaptive optics system has been set up and its performance was tested in the laboratory especially the closed-loop correction ability. This
adaptive optics subsystem is scheduled to be mounted at one folded Cassegrain focus of the 1.8-meter telescope this
year, and comparison test for star compensation observation using this compact system and conventional adaptive optics
system will also be carried out at the same time.
In 2013, a serial sky test has been held on 1.8 meter telescope in Yunnan observation site after 2011-2012 Laser guide star photon return test. In this test, the long-pulsed sodium laser and the launch telescope have been upgraded, a smaller and brighter beacon has been observed. During the test, a sodium column density lidar and atmospheric coherence length measurement equipment were working at the same time. The coupling efficiency test result with the sky test layout, data processing, sodium beacon spot size analysis, sodium profile data will be presented in this paper.
The Laser Guide Star Facility (LGSF) system of the Thirty Meter Telescope (TMT) will generate the artificial laser guide stars required by the TMT Adaptive Optics (AO) systems. The LGSF uses multiple sodium lasers to generate and project several asterisms from a laser launch telescope located behind the TMT secondary mirror. The laser beams are transported from a location below the primary mirror to the launch telescope using conventional optics to relay the beams along the telescope structure. The beams and relay optics are enclosed into hermetic ducts for safety reasons and to protect the optics against the environment. A Computational Solid Fluid Dynamics (CSFD) model of the LGSF ducts has been developed. It resolves the duct thickness, laser beam transfer lenses, mirrors and their framework for most of the laser beam path that is subject to significant temperature gradients and/or large vertical change. It also resolves the air inside the duct and its thermal interaction with the aforementioned components through conjugate heat transfer. The thermal interaction of the laser beam with the optics is also captured. The model provides guidance to the LGSF design team and a first estimate of the laser beam stability performance and requirement compliance. As the telescope structure design has evolved in the recent years, a new optical path has been proposed for the LGSF. Both the original and the new optical paths are compared against optical, mechanical and other telescope performance related criteria. The optical performance criteria include a first order analysis of the optical turbulence generated within the ducts. In this study simulations of the thermal environment within the ducts of the two candidate paths are performed and conclusions are drawn.
The TMT first light Adaptive Optics (AO) facility consists of the Narrow Field Infra-Red AO System (NFIRAOS) and the associated Laser Guide Star Facility (LGSF). NFIRAOS is a 60 × 60 laser guide star (LGS) multi-conjugate AO (MCAO) system, which provides uniform, diffraction-limited performance in the J, H, and K bands over 17-30 arc sec diameter fields with 50 per cent sky coverage at the galactic pole, as required to support the TMT science cases. NFIRAOS includes two deformable mirrors, six laser guide star wavefront sensors, and three low-order, infrared, natural guide star wavefront sensors within each client instrument. The first light LGSF system includes six sodium lasers required to generate the NFIRAOS laser guide stars. In this paper, we will provide an update on the progress in designing, modeling and validating the TMT first light AO systems and their components over the last two years. This will include pre-final design and prototyping activities for NFIRAOS, preliminary design and prototyping activities for the LGSF, design and prototyping for the deformable mirrors, fabrication and tests for the visible detectors, benchmarking and comparison of different algorithms and processing architecture for the Real Time Controller (RTC) and development and tests of prototype candidate lasers. Comprehensive and detailed AO modeling is continuing to support the design and development of the first light AO facility. Main modeling topics studied during the last two years include further studies in the area of wavefront error budget, sky coverage, high precision astrometry for the galactic center and other observations, high contrast imaging with NFIRAOS and its first light instruments, Point Spread Function (PSF) reconstruction for LGS MCAO, LGS photon return and sophisticated low order mode temporal filtering.
A composite tracking sensor, in which a reflect mirror with a central hole is inserted in the imaging systems so that the reflective beam beyond the hole is directed to the large dynamic range detector and the beam passing the hole is reimaged by a lens to enter the high sensitivity detector, can be used for tip-tilt detecting with high accuracy and large dynamic range simultaneously. A composite tracking sensor prototype based on the multi-anode photo-multiplier tubes (MAPMT) is developed for 1.8 meter astronomical telescope in the Gaomeigu astronomical observation station. In this paper, the principle of the composite tracking sensor is introduced. The prototype is described in detailed and the experimental results are presented. The results show that this composite tracking sensor can reach the tracking accuracy of 0.2 μrad and higher within the dynamic range of 870 μrad.
Institute of Optics & Electronics (IOE), Chinese Academy of Sciences (CAS) has more than 30 years’ experience on piezoelectric deformable mirror (DM) technologies research and developing since early 1980s. Several DMs of IOE have been used in many different application systems. A brief history of piezoelectric DMs development in IOE and several recently achievements, and the main characters, performance and test results of the DMs for astronomy will be presented in this paper. 1) High-order DM. DM prototype with 913-element for 4m telescope has been fabricated and tested in laboratory. 2) Adaptive Secondary Mirror (ASM). A 73-element ASM prototype with 12 microns stroke for 1.8m telescope has been fabricated. It will be installed onto the 1.8m telescope with a compact adaptive optics (AO) system. 3) Small spacing DM. A 6mm spacing 127-element DM based on the same construction with the High-order DM has been used in AO system of 1m New Vacuum Solar Telescope (NVST) in Yunnan Observatories. Higher density (3mm spacing) DM based on a novel construction has being developed. In 2012, the novel DM prototype with 100-element was fabricated and tested carefully in laboratory. Beside, a 6mm spacing 151-element DM based on the novel construction has being fabricated for the solar AO system.
Based on the demands of high sensitivity, precision and frame rate of tip/tilt tracking sensors in acquisition, tracking and pointing (ATP) systems for satellite-ground optical communications, this paper proposes to employ the multiple-anode photo-multiplier tubes (MAPMTs) in tip/tilt tracking sensors. Meanwhile, an array-type photon-counting system was designed to meet the requirements of the tip/tilt tracking sensors. The experiment results show that the tip/tilt tracking sensors based on MAPMTs can achieve photon sensitivity and high frame rate as well as low noise.
A microsecond pulsed sodium has been developed in TIPC laser physics research center, the power of this laser is
around 20W and the length of the pulse is about 120 microseconds. In 2011, an experiment to project the TIPC prototype laser to the sky and measure the photon returns of the laser has been held on the 1.8 meter telescope in Yunnan observation site. During the sky test, an artificial sodium beacon has been successfully generated, and the brightness of the sodium beacon is around 8.7M in V Band. In the 2012 test campaign, the sodium column density facility has mounted on the telescope to test the local sodium density and structure and the sodium density test result is around 2.2x1013/m2.
We provide an update on the development of the first light adaptive optics systems for the Thirty Meter Telescope
(TMT) over the past two years. The first light AO facility for TMT consists of the Narrow Field Infra-Red AO
System (NFIRAOS) and the associated Laser Guide Star Facility (LGSF). This order 60 × 60 laser guide star
(LGS) multi-conjugate AO (MCAO) architecture will provide uniform, diffraction-limited performance in the
J, H, and K bands over 17-30 arc sec diameter fields with 50 per cent sky coverage at the galactic pole, as
is required to support TMT science cases. Both NFIRAOS and the LGSF have successfully completed design
reviews during the last twelve months. We also report on recent progress in AO component prototyping, control
algorithm development, and system performance analysis.
In 2009, A 127-element adaptive system had been manufactured and installed at the Coude room of the 1.8-meter
telescope at the Gaomeigu site of Yunnan Astronomical Observatory, Chinese Academy of Sciences. A set of new
adaptive optical system based on a 73-element deformable secondary mirror is being developed and will be integrated
into the 1.8-meter telescope. The 73-element deformable secondary mirror with convex reflecting surface is designed to
be compatible with the Cassegrain focus of the 1.8-meter telescope. Comparing with the AO system of Coude focus, the
AO system on the deformable secondary mirror adopts much less reflections and consequently restrains the thermal
noise and increases the energy transmitting to the system. The design and simulation results of this system will be
described in this paper. Furthermore, the preliminary test result of the deformable secondary mirror in the lab is also presented.
The pyramid wavefront sensor is an innovative device with the special characteristics of variable gain and adjustable
sampling in real time to enable an optimum match of the system performance, which make it an attractive option for next
generation adaptive optics system compared with the Shack-Hartmann. At present most of the pyramid wavefront sensor
are used with modulation based on oscillating optical component in order to give a linear measurement of the local tilt,
but the PWFS without modulation would greatly simplify the optical and mechanical design of the adaptive optics
system and also give highest sensitivity as expected to be achieved. In this paper we describe the optical setup of our
adaptive optics system with nonmudulated pyramid wavefront sensor. In this system, the pyramid wavefront sensor with
8×8 sub-apertures in the pupil diameter has been designed, and the deformable mirror with 61 actuators based on the
liquid-crystal spatial light modulator is used to introduce aberrations into the system, as well as to correct them
afterwards. The closed-loop correction results of single order Zernike aberrations and the Kolmogorov turbulence phase
screen are given to show that the PWFS without modulation can work as expected for closed-loop system.
We are developing a sodium guide star adaptive optics system for the 1.8 meter telescope, which consists of three
main parts: (i) 20W microsecond pulsed laser system, (ii) Φ200mm laser launch telescope and (iii) 37-elements adaptive
optics system. All of these three parts are mounted on the 1.8 meter telescope which is located in Gaomeigu site of
Yunnan Astronomical Observatory, Chinese Academy of Sciences. The pulsed laser system and the launch telescope are
rotated with the azimuthal base of the telescope. A miniaturized 37-elements low-order adaptive optics system including
a 37-elelment deformable mirror and a 6x6 array Hartmann-Shack wavefront sensor is mounted at the Cassegrain focus
taking account of the pulsed laser mode. A separate tip-tilt correction loop is also integrated into the system. This paper
describes the details of this system, the simulation result and the test result in the lab. After the indoor test, the whole
system will be shipped to 1.8 meter telescope. The latest commissioning status and results is presented also in this paper.
We present the wavefront error budget and optical manufacturing tolerance analysis for 1.8m telescope. The error budget
accounts for aberrations induced by optical design residual, manufacturing error, mounting effects, and misalignments.
The initial error budget has been generated from the top-down. There will also be an ongoing effort to track the errors
from the bottom-up. This will aid in identifying critical areas of concern. The resolution of conflicts will involve a
continual process of review and comparison of the top-down and bottom-up approaches, modifying both as needed to
meet the top level requirements in the end.
As we all know, the adaptive optical system will correct for some of the telescope system imperfections but it cannot be
assumed that all errors will be corrected. Therefore, two kinds of error budgets will be presented, one is non-AO
top-down error budget and the other is with-AO system error budget.
The main advantage of the method is that at the same time it describes the final performance of the telescope, and gives
to the optical manufacturer the maximum freedom to define and possibly modify its own manufacturing error budget.
The 127-element adaptive optical system, which consists of a tracking loop with a tip-tilt mirror, a tracking system and a
tracking processor, and a wavefront correction loop with a 127-element deformable mirror, a Hartmann-Shack wavefront
sensor, and a wavefront processor, had been developed and integrated into the 1.8m astronomical telescope in September
2009. The First observations on the high resolution imaging for the stars had been done from September 23 2009 in the
first light to March 2010. In this paper, the 127-element adaptive optical system for 1.8m telescope is described briefly
and the star observation results in the first run are reported. The results show the angular resolution of the system can
attain or approach the diffraction limit of 1.8m telescope at I band (700nm-1000nm) and J band (1000nm-1700nm).
The 127-element adaptive optical system for the 1.8m astronomical telescope is being developed. In this system, the
wavefront correction loop consists of a 127-element deformable mirror, a Hartmann-Shack (H-S) wavefront sensor, and
a high-speed digital wavefront processor. The tracking system consists of a tip-tilt mirror, a tracking sensor and a
tracking processor. The wavelength for the H-S wavefront sensor ranges from 400-700nm. The imaging observation
wavelengths range from 700-1000nm and 1000-1700nm respectively. In this paper, the optical configuration of 1.8m
telescope will be briefly introduced. The 127-element adaptive optical system is described in detailed. Furthermore, the
preliminary performances and test results on the 127-element adaptive optical system is reported.
A kind of Multiple-Detecting-Branch (MDB) Shack-Hartmann wavefront sensor (SHWFS) with extremely large number
of subapertures, in which the pupil is split into spatially several branches by a beam splitter and each branch is detected
by a SHWFS with less subapertures comparatively, is proposed to use for the wavefront sensing of the adaptive optics
system for extremely large telescope. All the signals from the CCDs of SHWFS must be synchronized by the specially
developed hardware system. There are the angular error of the beam splitter and the circum-optical-axis rotary of CCDs
besides of the error of the conventional SHWFS. In this paper, the principle of the MDB SHWFS is introduced and its
errors are analyzed. The simulation and experimental results show that this kind of MDB SHWFS can be used to
measure effectively the wavefront aberration of the total pupil.
The adaptive optics can only partially compensate the image blurred by atmospheric turbulence due to the observing
condition and hardware restriction. A post-processing method based on frame selection and multi-frames blind
deconvolution to improve images partially corrected by adaptive optics is proposed. The appropriate frames which are
suitable for blind deconvolution from the recorded AO close-loop frames series are selected by the frame selection
technique and then do the multi-frame blind deconvolution. There is no priori knowledge except for the positive
constraint in blind deconvolution. It is benefit for the use of multi-frame images to improve the stability and
convergence of the blind deconvolution algorithm. The method had been applied in the image restoration of celestial
bodies which were observed by 1.2m telescope equipped with 61-element adaptive optical system at Yunnan
Observatory. The results show that the method can effectively improve the images partially corrected by adaptive
optics.
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