The Zwicky Transient Facility (ZTF) is a new time-domain survey project that will use a new camera with a 47 square degree field of view mounted on the Samuel Oschin 48-inch Schmidt telescope. To achieve good image quality over all sixteen 6K*6K CCDs (386mm＊395mm corner to corner), a trim plate was added in front of the existing cemented achromatic doublet to form an air-spaced triplet corrector. The trim plate is a Schmidt corrector using fused silica with 1348mm in diameter but only 15mm in thickness. The plate has been completed at NIAOT and already been mounted to the ZTF, the PSF seems very good.
The detailed fabrication process and testing to the trim plate from fine grinding to finish are presented in this paper, which includes CMM test, NULL test design, and Computer Controlled Polishing process developed at NIAOT.
The research works are summarized for Φ1.1m off-axis aspheric segments which are scaled-down TMT segments polished by NIAOT using SMAP (Stressed Mirror Annular Polishing) method in the previous phase and testing preparations for 1.45m mirrors. The detailed introduction is given on result of errors analysis in contact detection testing of segments. In the second part, the selected basis of sampling number for contact-type detector arrays and the terms number of Zernike polynomials we need are studied. And the situations on orthogonality destruction of Zernike polynomials in discrete points sampling case and spectral analysis for each order Spherical aberrations in continuous sampling are introduced.
A new type Stressed Mirror Polishing method using annular polishing machine is developed in NIAOT. It provides good efficiency for the massive production of off-axis segments for the extremely large telescope because 3 or more pieces of segment can be polished simultaneously on a AP machine. With an annular polishing machine with 3.6m diameter, two scale-down TMT segments have been polished. Both 2 segments are Φ1100mm in diameter, with the vertex radius of curvature of 60m and aspheric constant K=-1.000953. The off-axis distances (OAD) are 8m and 12m respectively. After SMAP process, the acceptable surface accuracy can be reached, which is 1.12μm/0.23μm of PV/RMS value for the segment with 8m OAD, and 1.22 μm/0.26 μm for another one.
In recent years, high frequency errors of mirror surface are taken seriously gradually. In manufacturing process of advanced telescope, there is clear indicator about high frequency errors. However, the sub-mirror off-axis aspheric telescope used is large. If uses the full aperture interferometers shape measurement, you need to use complex optical compensation device. Therefore, we propose a method to detect non-spherical lens based on the high-frequency stitching errors. This method does not use compensation components, only to measure Aperture sub-surface shape. By analyzing Zernike polynomial coefficients corresponding to the frequency errors, removing the previous 15 Zernike polynomials, then joining the surface shape, you can get full bore inside tested mirror high-frequency errors. 330mm caliber off-axis aspherical hexagon are measured with this method, obtain a complete face type of high-frequency surface errors and the feasibility of the approach.
The AST3 project consists of three large field of view survey telescopes with 680mm primary mirror, mainly for observations of supernovas and extrasolar planets searching from Antarctic Dome A where is very likely to be the best astronomical site on earth for astronomical observations from optical wavelength to thermal infrared and beyond, according to the four years site testing works by CCAA, UNSW and PRIC. The first AST3 was mounted on Dome A in Jan. 2012 and automatically run from March to May 2012. Based on the onsite winterization performance of the first AST3, some improvements such as the usage of high resolution encoders, defrosting method, better thermal control and easier onsite assembly et al were done for the second one. The winterization observation of AST3-2 in Mohe was carried on from Nov. 2013 to Apr. 2014, where is the most northern and coldest part of China with the lowest temperature around -50°. The technical modifications and testing observation results will be given in this paper. The third AST3 will be optimized from optical to thermal infrared aiming diffraction limited imaging with K band. Thus the whole AST3 project will be a good test bench for the development of future larger aperture optical/infrared Antarctic telescopes such as the proposed 2.5m Kunlun Dark Universe Survey Telescope project.
Chinese Antarctic Observatory has been listed as National large research infrastructure during twelfth five-year plan. Kunlun Dark Universe Survey Telescope, one of two major facility of Chinese Antarctic Observatory, is a 2.5-meter optic/infrared telescope and will be built at the Chinese Antarctic Kunlun Station. It is intended to take advantage of the exceptional seeing conditions, as well as the low temperature reducing background for infrared observations. KDUST will adopt an innovative optical system, which can deliver very good image quality over a 2 square degree flat field of view. All of parts of it have been designed carefully to endure the extremely harsh environment. KDUST will be perched on a 14.5-meter-high tower to lift it above the turbulence layer. In this paper, preliminary design and key technology pre-research of KDUST will be introduced.
Optical plates (OP) play more and more important role in modern ground-based telescopes. They can be as segments
composing primary mirror, deformable mirror for correcting air turbulence or active stressed lap used in polishing large
aspherical optics. When control the deformation of these plates, we always confronts with common situations: high
shape precision requirement, rapid deformation frequency with real time demand, intrinsic multi-channel coupling
characteristic. So how to improve OP deformation performance becomes a critical task in practical design. In this paper,
the control principle of OP is first introduced. Then a three-layer control architecture is presented. They are application
layer, real time control layer and motion execution layer. After that we designed a prototype system following this
framework, targeting active stressed polishing lap which has twelve motion channels. Both the hardware and software
development are discussed thereafter. OP surface deformation experiments are carried out and surface shape obtained
using LVDT array. Results verify the effectiveness of the design. And we are looking forward to use this control design
in more channel and time demanding applications.
The test method of Large-diameter convex secondary mirror in development process is the key to making large
telescope technology. Classical means HINDLE to test using of non - aberration points needs a spherical reflecting
mirror which larger than the secondary mirror several times. This new Hindle test method based on stitching
technology can significantly reduce their standard mirror's size, drop the difficulty of processing and cut down the
costs. In This paper, the Hindle testing basic principles which base on stitching technology is introduced firstly, then
principle of stitching and least square method. Following the parameters of inside and outside standard mirrors are
derived. Then translation and rotation transformation algorithm of different sub-aperture interferometer array data is
given. Finally the preliminary results of the radial stitching experiments are given. The results showed that the relative
error is RMS = 6.1%, PV = 5.11%. With improving and perfection, this method can be used in the E-ELT, CFGT
convex secondary mirror telescope test.
To obtain high resolution infrared image, both low photon efficiency and long wavelength of infrared light requires
enough large aperture telescope, but large aperture vacuum windows can hardly achieve high optical quality, so open
structure becomes the only viable choice for large infrared solar telescope. In addition to the effects of atmospheric
turbulence, open solar telescopes suffer from the heating of the optics by sunlight, especially primary mirror heating.
These factors cause the image to shiver and become blurred, and increase infrared observing noise. Since blowing air
across the front surface of the primary mirror doesn't have the necessary heat transfer coefficient to remove the absorbed
heat load, it must be cooled down to maintained at a temperature between 0K and 2K below ambient air temperature to
reduce the effects of turbulence. This paper will introduce some cooling methods and simulation results of primary
mirror in large infrared solar telescope. On the other hand, mirror material with nice thermal conductivity can reduce the
temperature difference between mirror surface and air, and mirror surface polishing at infrared wavelength can be
comparatively easier than at visible wavelength, so it is possible to select low cost metal mirror as primary mirror of
infrared solar telescope. To analyze the technical feasibility of metal mirror serving as primary mirror, this paper also
give some polishing results of aluminum mirror with electroless nickel coating.
Prelimenary site testing led by Chinese Center of Antarctic Astronomy (CCAA) shows that the highest point of the
Antarctic Plateau Dome A has very clear sky, good seeing, slow wind, low boundary layer and very low precipitable
water vapour which make it the best site on earth for optical/IR and sub-mm observations. Chinese Small Telescope
ARray (CSTAR) was installed at Dome A in 2008 and have automatically observed for about 3 antarctic winters. The
three Antarctic Schmidt telescopes(AST3) with entrance pupil diameter 500mm are the second antarctic project
proposed by CCAA and the first AST are being constructed in NIAOT now which is planned to be mounted on Dome A
at the beginning of 2011. All the tracking components were tested in the low temperature chamber and an adaptive
defrosting method is designed to prevent the frost building up on the schmidt plate.
Off-axis systems in radio and infrared wavelengths have obvious advantages in suppressing aperture blockage and
background noise. Therefore, the signal-to-noise ratio as well as system gain is improved. However, an off-axis optical
system involves complex aberrations which limit its field of view. This paper provides an overview of aberrations in
axial symmetric and off-axis optical systems. As the system deviates from an axial symmetric one, system aberrations
become more and more complicated. In a general two mirror off-axis focusing system, the field of view is nearly zero.
Even for off-axis system with an equivalent parabola, the field of view is still very small as the linear astigmatism
dominates the system. An optimized off-axis system is one in which the linear astigmatism and cross polarization-free
conditions are met. In this optimized system, coma aberration is dominant, so that the field of view is still limited. The
field of view of an optimized off-axis system can be improved using a simple coma corrector system.
Nanjing Institute of Astronomical Optics & Technology (NIAOT) is investigating two types of sub-aperture polish
technique for manufacturing aspheric components in large astronomical telescopes. One technique is computer
controlled optical surfacing (CCOS). It removes material by a small polish tool through traditional mechanical and
chemical process. The other is ion beam figuring (IBF) technique. It employs a neutralized ion beam to physically
sputter material form optical surface. Although the basic mechanism of the two techniques is different, they true share
the same mathematical model and fabrication diagram which will be put forward firstly in this paper. Then tool design
and material removal function in CCOS will be studied following by a fabrication instance using CCOS. After that some
recent progresses achieved in IBF is presented. The last part will focus on the complementary relationship of CCOS and
IBF. Using them alternatively optimal combination of surface precision, efficiency and edge control could be obtained.
Simulation is provided to support this view and experiment will be done in near future.
We have produced a series of reflective mirrors using the newly installed 1.6m evaporation chamber at the Nanjing
Institute of Astronomical Optics and Technology (NIAOT) of the National Astronomical Observatories of China. The
main task of this equipment is to coat the mirrors of the LAMOST. The chamber have thermal evaporation system,
electron beam source, ion beam source, quartz crystal deposition controller and optical monitoring system, so can
evaporate all kinds of metal and oxide film and effectively control film thickness. Now, we have utilized this chamber to
aluminize the mirrors of LAMOST primary mirror, the average reflectivity is above 89% in the wavelength range from
370nm to 900nm. Recently, we have completed the enhanced silver reflector experiment, by controlling the dielectric
layers optical thickness, the reflectivity is increased from 370nm to 400nm. The average reflectivity of enhanced silver
reflector is above 97% in the wavelength range from 370nm to 900nm.
During operation, astronomical telescope will undergo thermal disturbance, especially more serious in solar telescope,
which may cause degradation of image quality. As drives careful thermal load investigation and measure applied to
assess its effect on final image quality during design phase. Integrated modeling analysis is boosting the process to find
comprehensive optimum design scheme by software simulation. In this paper, we focus on the Finite Element Analysis
(FEA) software-ANSYS-for thermal disturbance analysis and the optical design software-ZEMAX-for optical system
design. The integrated model based on ANSYS and ZEMAX is briefed in the first from an overview of point.
Afterwards, we discuss the establishment of thermal model. Complete power series polynomial with spatial coordinates
is introduced to present temperature field analytically. We also borrow linear interpolation technique derived from shape
function in finite element theory to interface the thermal model and structural model and further to apply the
temperatures onto structural model nodes. Thereby, the thermal loads are transferred with as high fidelity as possible.
Data interface and communication between the two softwares are discussed mainly on mirror surfaces and hence on the
optical figure representation and transformation. We compare and comment the two different methods, Zernike
polynomials and power series expansion, for representing and transforming deformed optical surface to ZEMAX.
Additionally, these methods applied to surface with non-circular aperture are discussed. At the end, an optical telescope
with parabolic primary mirror of 900 mm in diameter is analyzed to illustrate the above discussion. Finite Element
Model with most interested parts of the telescope is generated in ANSYS with necessary structural simplification and
equivalence. Thermal analysis is performed and the resulted positions and figures of the optics are to be retrieved and
transferred to ZEMAX, and thus final image quality is evaluated with thermal disturbance.
For currently market available levelmeter can not meet the requirement for measuring the azimuth mounting of the LAMOST, this paper presents a novel design scheme of an opto-electronic levelmeter with needed high precision. The levelmeter is essentially a combination of an optical front end and a computer aided measuring back end. The light from a point source is firstly turned to be parallel and reflected by a tip-tilt mirror which keeps pointing to the zenith and then imaged onto a CCD target through optical system, afterwards, the position of the image spot is processed by computer software to give measurement results. By rotating the LAMOST mounting about azimuth axis with the levelmeter on it, the axis system is measured, and if the measured azimuth axis is not perpendicular enough, the image spot on CCD target is to offset some distance by which the tilt angle of the axis can be evaluated. The design principle and data processing of the levelmeter are detailed systematically in this paper. Experiment results confirmed that the accuracy of the levermeter is up to 0.043" beyond that required by the technical specification of the LAMOST. Also, the novel levermeter is applicable to measuring azimuth axes of other telescopes.
An extremely large telescope named Chinese Future Giant Telescope (CFGT) has been presented. The primary mirror of CFGT is a 30-meter diameter hyperboloid with a focal ratio F/1.2 and it consists of over one thousand of sector-shaped segments with the size about 1.1-meter in diagonal. Based on the optical design concept and the experience of existing large segmented primary mirror, we explore the segment fabrication and testing issues in this paper. The relationship between external contour, the size and the asphericity of sub-mirror is studied. Two potential segment fabrication approaches for mass-production-scale are discussed. One is the optical replication. The other is stressed-mirror polishing. Both of two processes are tightly combined with several key techniques and devices, the ion-beam figuring, large annular polisher, and the stressed lap. Some preliminary concepts for testing of l-meter class convex/concave off-axis aspheric surface are discussed.
In wide linear-field of view, large relative aperture mirror system, it is unavoidable to use high order aspheric surfaces. In this paper the design of the compensators for testing the secondary and the tertiary mirror of a 3 mirror system is described. The surfaces under testing have high order up to r16. The diameter of the secondary is 112 mm, radius of curvature is 211.462 mm, and the conic constant is 0.07744075. The diameter of the tertiary is 272 mm, radius of curvature is 197.722 mm, and the conic constant is 0.2623604. Three elements and four elements compensators have been designed. The residual aspherical aberration has been minimized to about λ/20.
An ellipsoid mirror with Φ500 mm aperture has been successfully manufactured by NAIRC. The parameters of the mirror are as follows: diameter is Φ500 mm, radius of curvature is 1996 mm, conic constant k=-0.9545, requirements of surface accuracy are λ/10 (P-V) and λ/40 (RMS), (λ=632.8 nm). Based on the surface type, three kinds of test optics are designed. The errors of the elements in the testing optical path are analyzed. The small tools are used to figure the asphericity of the mirror. Finally surface accuracy of λ/10 (P-V) and λ/50 (RMS) are reached.