Absolute calibration of photomultiplier based detectors - difficulties anduncertainties

Photomultiplier manufacturers can provide a calibration of quantum efficien cy over a range of wavelengths with an accuracy of up to 2%. To convert the se figures to absolute counting efficiency requires knowledge of photomulti plier collection efficiency, F. Traditional methods for determining F are d iscussed with emphasis on sources of error. Light sources emitting at a kno wn photon rate allow the absolute quantum efficiency to be determined direc tly. It is important in all attempts at absolute calibration to appreciate the conditions which manufacturers apply when calibrating photomultipliers. (C) 1999 Elsevier Science B.V. All rights reserved.