LRS's CCD

Quantum Efficiency

The CCD quantum efficiency (QE) was measured in the wavelength interval 2000 10500 Å in incremental steps of 500 Å. The CCD was illuminated using monochromatic light obtained through a Xenon lamp, a series of filters and a monochromator. The signal integrated on the CCD is then compared to the response of a calibrated photodiode.

Quantum efficiency

Dark Current

The dark current is measured taking a short dark exposure and a long dark exposure. The signal level in the two exposures is then compared. The frame is divided in 10×10 pixel sub-frames and the dark current is computed for each of them. The average value of the dark current turns out to be 6 electrons/pixel/hour.

Charge Transfer Efficiency

The charge transfer efficiency (CTE) is measured using the X-ray stimulation method. In particular, the parallel CTE is obtained exposing the CCD to the Fe55 source for a given amount of time. After integration, the columns are stacked together and the signal is plotted versus the number of pixel transfers. The CTE is then given by CTE= 1- (Charge loss)/1620 e^-/N

1 - ( s(0) - s(4095) ) / ( s(0) * 4096)

The LORAL CTE turned out to be 0.999982.

CCD Image

The image area of the CCD is 2048 X 2048 pixels, the length of the output register is 2048 pixels. The dimension of the image produced by the acquisition system is 2048×2100 pixels (without binning). This means that the overscan zone depends by the readout mode and by the binning utilised.
The User Interface allows different acquisition modes and different binning on chip. In Table 1 the overscan zone for the different kind of acquisition are showed.

Table 1: Loral CCD at different read-out modes.
Readout Mode	Binning	Image Size	X prescan	X image	X Overscan	Y overscan
Left	1 X 1	2048 X 2100	NO	0 - 2047	NO	2048 - 2099
Right	1 X 1	2048 X 2100	NO	0 - 2047	NO	2048 - 2099
Two outs	1 X 1	2048 X 2100	NO	0 - 2047	NO	2048 - 2099
Left	1 X 2	2048 X 1050	NO	0 - 2047	NO	1024 - 1049
Right	1 X 2	2048 X 1050	NO	0 - 2047	NO	1024 - 1049
Two outs	1 X 2	2048 X 1050	NO	0 - 2047	NO	1024 - 1049
Left	2 X 2	1024 X 1050	NO	0 - 1023	NO	1024 - 1050
Right	2 X 2	1024 X 1050	NO	0 - 1023	NO	1024 - 1050
Two outs	2 X 2	1024 X 1050	NO	0 - 1023	NO	1024 - 1050

For any comments please contact Rosario Cosentino.