Prototype system and CCD test results

To test the performance and the functionality of the curvature CCD, a laboratory system has been built to allow independent testing without the need to interface to a full adaptive optics system.

An integrating sphere and a stable light source were used to simulate the membrane movement and providing the light signal for CCD characterization.
An Oeffner relay optics was designed (consisting of two spherical, reflecting surfaces) to re-image the light of the fibers 1:1 onto the superpixels and a fiberfeed with 60 individual fibers plus 4 additional fibers for the tip/tilt sensor to feed the subapertures of the CCD with light.

Laboratory detector system

A read out noise of less than 1.5 electrons was achieved for all read out ports including the tip/tilt sensor at a read out speed of 4000 frames per second.

With all pixels per read out port binned into 12 superpixels, it was possible to read the serial register relatively slowly at 50 kilopixels per second. The plot shows read out noise and conversion factor versus drainvoltage.

Optimal bias setting for the drain voltage of the MOSFET amplifier

Vertical and horizontal CTE better than 0.99999 down to lowest light levels

Residual non-linearity better than 0.5 % / -0.5 %. (peak to peak)

Negligible amount of dark current at 197 Kelvin (0.25 electrons per subaperture at 50 Hz frame rate)

Measured responsivity of the CCID-35: 14.2 µV/electron ± 5 %.

Very good cosmetic quality

Low light level performance

To verify the capability of the CCID-35s to move very small charge packets with high efficiency, the input illumination on the fiber entrance was turned down with neutral density filters to give a signal of ~1 electron per pixel per exposure. The signal produced in the fiber spots is almost not visible and embedded in the noisy trace of the readout noise. Hence 256 exposures with the same illumination level were summed up and normalized.
Horizontal cross section of single exposure frame	Horizontal cross section of the average frame of 256 exposures
CCD image with ~1 electron charge per pixel and a readout noise of 1.4 electrons and its horizontal cross section.	Average frame of 256 CCD images with ~1 electron charge per pixel and a readout noise of ~0.1 electrons and its horizontal cross section.

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Last update: Jan 27, 2003
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