As there are no optics within the cryostat, the angle 0 (maximum 18 degrees in the case of CRIRES) defines the intensity of illumination across the detector array. The illumination for off axis points on the detector mosaic falls off. For Q as the solid angle on axis, the solid angle off the axis at an angle of 0 will be Q cos30. Since the illumination falls obliquely at an angle of 0, there is a further factor of cos 0. Therefore the off axis illumination falls by cos40. Figure 5 shows a diagram used for the correction of the CRIRES mosaic together with an image of the four detectors masked by the pinhole grid mask. Hence it is possible to calculate the exact flux on the detectors to obtain the quantum efficiency.

Figure 5. Illumination distribution and map of efficiency for the CRIRES mosaic.

Figure 5. Illumination distribution and map of efficiency for the CRIRES mosaic.

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