GERB 4 detector spectral response measurements J E Russell Imperial College, London j.e.russell@imperial.ac.uk

New LU coated FM3 For GERB 4, 4 new detector wafers were coated with gold-black at LU One was chosen for flight and spectral response measurements made, this detector has subsequently had to be replaced, but the response measurements have been analysed and are reported here.

Full beam measured by reference pixel, corresponds to what reference detector sees. Locations at which all pixels measured also characterised by reference pixel

Reference detetector response

Response uncorrected for window transmission

5% discontinuity where reference detectors are swapped

LU detector spectral response

LU detector spectral response

LU detector spectral response

Summary The new measurement procedure appears to work. Measurement on the newly coated detectors shows the response drops steadily and at around 1.3m is about 25% lower than at 20m A discontinuity between 0.9 and 1.3m in the window transmission measurements introduces a further apparent 5% drop in response for wavelengths shorter than 1m, this is being investigated further. Undulating variation in response is apparent on top of the overall drop off which is similar to variations observed in witness sample and theoretically expected Pixel to pixel variability in response appears primarily to be broad scale across the detector array, and probably relates to variations in thickness of the gold black