ABSTRACT
For segmented telescopes, achieving fine co-focus adjustment is essential for realizing co-phase adjustment and maintenance, which involves adjusting the millimeter-scale piston between segments to fall within the capture range of the co-phase detection system. CGST proposes using a SHWFS for piston detection during the co-focus adjustment stage. However, the residual piston after adjustment exceeds the capture range of the broadband PSF phasing algorithm( ± 30µm), and the multi-wavelength PSF algorithm requires even higher precision in co-focus adjustment. To improve the co-focus adjustment accuracy of CGST, a fine co-focus adjustment based on cross-calibration is proposed. This method utilizes a high-precision detector to calibrate and fit the measurements from the SHWFS, thereby reducing the impact of atmospheric turbulence and systematic errors on piston measurement accuracy during co-focus adjustment. Simulation results using CGST demonstrate that the proposed method significantly enhances adjustment accuracy compared to the SHWFS detection method. Additionally, the residual piston after fine co-focus adjustment using this method falls within the capture range of the multi-wavelength PSF algorithm. To verify the feasibility of this method, experiments were conducted on an 800mm ring segmented mirror system, successfully achieving fine co-focus adjustment where the remaining piston of all segments fell within ±15µm.
ABSTRACT
Large aperture ground-based segmented telescopes typically use electrical edge sensors to detect co-phase errors. However, complex observing environments can lead to zero-point drift of the edge sensors, making it challenging to maintain the long-term co-phase of the segmented primary mirror using only edge sensors. Therefore, employing optical piston error detection methods for short-term calibration of edge sensors can address the issue of zero-point drift in the sensors. However, atmospheric turbulence can affect calibration accuracy based on the observational target. To achieve high-precision calibration of electrical edge sensors, this study investigates the impact of atmospheric turbulence on optical piston error detection. Based on simulated results, it is found that the actual measured piston error in the presence of atmospheric turbulence is the difference between the average phases of the two segments. Subsequently, optical piston error detection experiments were conducted in a segmented mirror system under simulated turbulent conditions with varying turbulence intensities. Experimental studies have shown that the detection accuracy of the optical method is almost the same as without turbulence when using a detection aperture size that is 0.82 times the atmospheric coherence length and an exposure time of at least 40 ms. The root mean square of the cross-calibration is better than 3 nm. These experimental results indicate that under conditions of good atmospheric seeing, the optical piston error detection method can meet the short-term calibration requirements of edge sensors by setting reasonable detection area size and exposure time. It may even be possible to directly use optical detection methods to replace edge sensors for real-time detection of piston errors.
ABSTRACT
An 8 m ring aperture segmented telescope is one of the important elements of the Chinese Giant Solar Telescope (CGST) project. In addition, active control of the primary mirror has become a key technology of the 8 wm ring solar telescope (8 m RST). Due to the particularity of the ring aperture, the active maintenance of the segmented RST faces the following problem: edge detection cannot provide enough information to fulfil the closed-loop control. A scheme of using edge and tip detection to complete the active maintenance of an 8 m RST has been proposed. To study the feasibility and performance of edge detection combined with tip detection, we built a workbench of a two-segmented mirror and carried out an active maintenance analysis and experiment. Two capacitive sensors were used to detect the edge height change between the segments, and a Shack-Hartmann sensor was used to detect the tip and tilt change of the segment. A stable mirror figure was achieved during 100 min, and the mirror figure error was maintained at 18.94 nm. This work will provide reference for the implementation of the active control for a segmented ring telescope and also give evidence for the choice of the primary mirror of the CGST.
ABSTRACT
The active control of a primary mirror for a ring aperture segmented telescope is different from that of a full aperture segmented telescope. Two active maintenance proposals for the ring telescope designed from the segmented patterns are outlined. We present a preliminary calculation of noise propagation and analysis of primary mirror mode characteristics for each proposal. The modulation transfer functions (MTFs) of the primary mirror corresponding to each maintenance method at several typical working wavelengths are also simulated.
ABSTRACT
A simple, sensitive, reliable and flexible flow injection spectrophotometric method is proposed for on-line preconcentration and determination of trace amounts of zinc in water. At the presence of Tween-80 in pH 9.3 buffer solutions, the shade of color of Zn (II)-PAN complex is in a linear relation to the zinc amount at the point of the maximum absorption peak of 560 nm. The optimal experimental conditions, including reaction conditions and preconcentration conditions, had been obtained. The linear range of the proposed method was between 2.0 and 360 mug L(-1) and the detection limit was 0.42 mug L(-1). The relative standard deviation was 3.55% and 2.14% for 5.0 mug L(-1) and 50 mug L(-1) of zinc standard solution (n = 8). The method had been successfully applied to zinc determination in water samples and the analytical results were satisfactory.
