Along with development and progress of modern optics manufacturing technology and optical test technology, there are
a series of modern polishing technologies based on the application of computer software and hardware, such as
CCOS(Computer Controlled Optical Surfacing), Stress Lap Polishing, Magnetorheological Finishing, Ion Beam Milling,
etc. The emergence of these new technologies promotes aspherical mirrors widely used in optical system. Vacuum
evaporation technique is applied widely on making optical coating. In this paper, we discuss the feasibility on applying
vacuum evaporation technique to making large-size aspherical mirrors. The technology is to take original sphere as
substrate, deposit film of certain thickness distribution on the surface, then get aspherical mirror. This technology has a
special advantage and tremendous development space in the off-axis aspheric processing, silicon carbide aspheric surface
processing and modification, super-glossy aspheric processing and great telescope mirror batch processing.
Proc. SPIE. 7658, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronic Materials and Devices for Detector, Imager, Display, and Energy Conversion Technology
KEYWORDS: Observatories, Telescopes, Mirrors, Astronomy, Control systems, Domes, Astronomical telescopes, Optical instrument design, Control systems design, Temperature metrology
Preliminary site testing shows that Antarctic inland Dome A is likely to be the best astronomical observatory site on the
ground, Chinese first Antarctic astronomical equipment CSTAR has been successfully run Dome A. Three Antarctic
Schmidt Telescopes (AST3) is the next important Antarctic astronomical equipment, one of which will be mounted
Dome A. In the year of 2010, and the three will be installed Dome A finally. Because of the very low temperature and
saturation vapor pressure, and the temperature gradient changes fast near the ground layer at Dome A, the mirror is easy
to be frosted, which is one of difficulties to AST3.Indium Tin Oxide (ITO)is an N-type semiconductor material, because
it has few resistors, good light transmission, good weather resistance, small environmental impact, low cost, and it is
easy for large area coating, so it is widely used in many fields. The mirror is heated by ITO that is coated on the surface
of the mirror, the voltage on the ITO will be tuned by changing the output pulse width, and then the system achieves a
closed-loop control. The difference between the mirror temperature and ambient temperature will be maintained in an
ideal range, and this will not only ensure that the mirror surface will not get frosting, but to minimize the impact of
mirror seeing to guarantee the image quality of the telescope. The experimental results show that the temperature control
system can control the different temperature between the mirror surface and the ambient less than 2 degree in real time,
which can improve the mirror's working environment, and the overall effectiveness of the telescope's observations.
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.
Fabry-Perot interferometer has an important effect on near-infrared high spectral resolution spectrograph. In 1896, Ch. Fabry and Alfred Perot designed and used the Fabry-Perot interferometer for the first time. Since then the instruments using Fabry-Perot interference phenomena have been applied broadly to multi-field, such as astronomy, laser, and fiber-optic transmission. Fabry-Perot interferometer has many advantages such as narrow passband, high spectral resolution, high throughput, easy wave-length adjustment, simple structure and large aperture. Comparing with traditional visible light, the solar observation in near-infrared has many advantages: for example, weaker magnetic field strength can be more precisely measured with near-infrared spectrum .So developing the key technology of near-infrared high spectral resolution spectrograph--Fabry-Perot interferometer has become urgent.
For developing near-infrared Fabry-Perot interferometer, there are four difficulties: producing high quality optical plane: peak-to-valley surface flatness better than λ/100; coating Fabry-Perot interferometer plates with broadband multilayer dielectric films(including spectrum performance, thickness uniformity and stress effects); controlling the distance of interference cavity; keeping constant temperature.
In this paper, the process of designing broadband dielectric reflective and antireflective coatings applied in near-infrared Fabry-Perot is described and some problems of designing Fabry-Perot interferometer are discussed: the design of broadband dielectric mirror is described with reflectivity of 93.9±1.0% over spectral ranges from 1.0μm to 1.7μm; by reflective phase shifts in the design of mirror coating, computing the required film thickness uniformity atλ/100 of peak-to-valley surface flatness; degradation of surface figure is perhaps more thanλ/100 even if the soft coating materials-zinc sulfide and cryolite are used, and in order to reduce the degradation of surface figure brought by the stress of dielectric mirror coating, antireflective coating adopts same materials of dielectric mirror coating, ZnS and Na3AlF6, and similar film total thickness.