Indoor air turbulence had a certain degree of influence on optical testing or optical system image quality. A long optical testing path was built in tower which was one of the largest vertical towers for optical testing in China with about 23-meter high. The relevant influence characteristics were measured and studied in a specific state. First, the air turbulence was formed using air conditionings. Then, the optical wave fronts were sampled by interferometer with two conditions of undisturbed situation and disturbed situation in which the air conditioners were turned on for a while and then turned off some time and sampling was beginning. After the statistical analyzing to the sampling results, the following several evaluation results of image quality were acquired in different status, the Radius of Encircled 80% Energy (REE), the evaluation factor of modulation transfer function (MTF), the Strehl Ratio (SR), the traditional evaluation method PV/RMS value of wave fronts, and the turbulent correlation length of atmospheric r0. The statistical calculation results showed that turbulence intensity increased and optical image quality was deteriorated after air disturbed.
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.
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.
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.
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.