A large ion beam figuring plant which can process up to 1.5m mirror in diameter has been developed. The plant adopts
five axes scanning mode. The mirror with which the five axes scanning system is set face to face is placed vertically
when working that can reduce the adverse effect of the flour dust to the mirror and the ion source. The mirror and the
five axes scanning system are installed on two doors respectively. The open-close type of the door is a hanging bridge
type. And the door will be horizontal when completely opening that will be convenient for installing the mirror and
maintaining the system. Two software which are used for calculating the dwell-time and controlling the five axes system
are programmed. The five axes system will always keep normal direction following when working.
The ion beam figuring is a kind of advanced technology of mirror processing. It has the advantages of high processing
precision, high speed and no damage to the mirror surface. The ion beam figuring machine is established by using a one
meter diameter vacuum coating plant in this research project. Mechanical scanning device, ion source and workpiece
make up of the machine. Water, electricity and gas will be imported to the vacuum chamber. The computer software,
extracting the error function between the ion beam processing function and mirror surface function by using the data of
interferometer measuring, will calculate the dwell-time function in the course of processing. The computer will control
the whole process based on the dwell-time function. The experiment processing indicates that PV will reach 1/14λ and
RMS will reach 1/70λ by once ion beam figuring.
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.
Introduction to design thought of a large vacuum sputtering coating plant for astronomical telescope. The coating plant is square and all working cells are installed on a holder inside the chamber. When the plant door open, the holder with working cells is hauled out of chamber, then maintaining, repair and installing mirrors are very easy.
Metal film and dielectric film are made with DC and RF magnetron sputtering respectively. The largest diameter of mirror is 1600 mm and the diameter of sputtering target is 160 mm. The whole mirror is coated by the polar coordinate scanning through computer control.
There are three advantage: large mirror is sputtered with small power supply, so the cost is saved; By computer controlling working parameter of scanning, better uniformity can achieve; scanning sputtering can correct the mirror surface.
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.