The color dependence of the measured decline of the on-orbit sensitivity of the FUV channel of the HST Cosmic Origins
Spectrograph (HST-COS) indicated the principal loss mechanism to be degradation of the cesium iodide (CsI)
photocathode of the open-faced FUV detector. A possible cause of this degradation is contamination by atomic oxygen
(AO), prompting an investigation of the interaction of AO with CsI. To address this question, opaque CsI photocathodes
were deposited on stainless steel substrates employing the same deposition techniques and parameters used for the
photocathodes of the HST-COS FUV detector. The as-deposited FUV quantum efficiency of these photocathodes was
measured in the 117-174 nm range. Several of the photocathodes were exposed to varying levels of thermalized, atomic
oxygen (AO) fluence (produced via an RF plasma). The post AO exposure QE's were measured and the degradation of
sensitivity versus wavelength and AO fluence are presented.
TUnable Antenna-Coupled Intersubband Terahertz (TACIT) detectors use semiconductor quantum well heterostructures to offer tunable detection of light at few-Terahertz frequencies. TACIT detectors have been predicted to have background-limited sensitivity for a 300 K blackbody when operating in either a bolometric or non-bolometric mode. The speed of detection is expected to be 1 ns to less than 10 ps depending on the operating electron temperature and device dimensions. A planar metal antenna couples the incident Terahertz radiation from free space to the quantum well heterostructure. Electrons in the quantum well absorb the radiation, exciting them from the first to the second energy subband. The absorption frequency of the intersubband transition can be tuned by applying a voltage across the device. The quantum well heterostructure is designed so that the subbands have different electron mobilities. Absorption changes the relative number of electrons in each subband, and the effective mobility of the device changes. A current is applied to the active area of the quantum well, and the change in effective mobility is detected as a change in the in-plane resistance of the device. TACIT detectors are being fabricated. Modeling and experimental progress will be discussed.