The QE chamber allows the user to measure the quantum efficiency of CCID-17 devices. The chamber provides a steady flux of X-rays incident on two CCDs, which lie on a translation stage. Thus, one test CCD can be cross- calibrated against a reference CCD.
The apparatus consists of a large vacuum vessel, fitted with a liquid nitrogen flow system to allow cooling of the chips. The chamber has two sources of X-ray photons: the HEXS (High Energy X-ray Source) and tritium excited targets. A two-dimensional translation stage moves the two devices in and out of the source beams. The chamber also includes an alignment system of LEDS and pinholes to enable positional reproducibility of the CCDs with respect to the sources.
The QE chamber allows the QE measurement of one chip to be transfered to another. The translation stage first moves the previously calibrated chip into one of the incident beams in order to determine the beam's flux. The translation stage then moves the uncalibrated device into the same beam, and its QE is determined at that energy.
Each flight device needs its QE measured over a range of energies. The HEXS source produces photons between 1.74-8.05 keV. Various targets are rotated into a beam of electrons to produce the different lines. In addition, radioactive decay of Fe-55 produces a Mn-k (5.9 keV) line. Beta decay of tritium sources excite O-k (.525 keV) and F-k (.677 keV) lines and provide the flux necessary for low-energy QE determination.