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CCD Camera

LAMOST has 32 CCD cameras. CCD chip is scientific CCD sensor with 4096×4136 active pixels. There is a red brand CCD camera and a blue band CCD camera for each spectrograph. They can read out image with a very low readout noise by two output channels for each chip. With a speed of 200Kpix/s, CCD cameras can read out a full image in 40 seconds, while the readout noise is less than 4 electrons.

Spectrum of light beam from fibers (arranged along a 144 mm height slit from each spectrograph) is imaged onto 32 pieces of 4096×4096 EEV CCD chips with 12μm square pixel size. The full width half maximum (FWHM) of monochromatic images is about 7-9 pixels. Dispersion of the red band is about 0.084nm/pixel, and the dispersion of the blue band is 0.057 nm/pixel.

The 32 CCDs for low resolution spectrographs are EEV CCD203-82 scientific CCD sensors with different coating. The 49.2mm x 49.2mm image area of a chip has its flatness better than 15 μm with 100% active area. The back-illuminated spectral response combined with very low read-out noise give exceptional sensitivity. There are extra rows of pixels such that the total number is actually 4096 horizontal by 2 × 2068 = 4136 vertical. The register and output capacities are designed to allow full capacity 2 × 2 binning, so that the device may be operated efficiently as a 2048 × 2068 24 μm-pixel imager.

The performance (at 173K unless stated) of the CCD cameras is as: