HYBRID PHOTODETECTORS FOR SUPERCONDUCTING SUPER COLLIDER CALORIMETRY

AVALANCHE PHOTODIODES THAT HAVE LARGE AREA (CURRENTLY 17 MM ACTIVE-AREA DIAMETER BUT POTENTIALLY UP TO 75 MM), UNIFORM HIGH GAIN, AND LOW NOISE, WHEN COMBINED WITH A HIGH VOLTAGE VACUUM PHOTODIODE "FRONT END," MAKE POSSIBLE A HYBRID PHOTODETECTOR THAT COMBINES THE STRENGTHS OF PHOTOMULTIPLIERS AND SOLID-STATE PHOTODETECTORS. THE HYBRID HAS THE PHOTO RESPONSE OF A CONVENTIONAL PHOTOMULTIPLIER. IT CAN HAVE THE EXTREMELY LOW DARK CURRENT OF AN S-20 PHOTOCATHODE, OR IT CAN HAVE A TAILORED SPECTRAL RESPONSE, SUCH AS A SOLAR-BLIND ULTRAVIOLET RESPONSE. AT THE SAME TIME, THE HYBRID HAS MANY OF THE ADVANTAGES OF SOLID-STATE PHOTODETECTORS, SUCH AS SIMPLICITY, COMPACTNESS, RUGGEDNESS, VERY LARGE DYNAMIC RANGE, AND FREEDOM FROM AFTERPULSING. IN A PROXIMITY-FOCUSED VERSION, THE HYBRID OFFERS INSENSITIVITY TO EXTERNAL MAGNETIC FIELDS, WHILE IN AN INTERNALLY PROCESSED VERSION IT OFFERS THE POTENTIAL FOR EXTREMELY LOW COST. IN CERTAIN RESPECTS, SUCH AS ITS NEARLY IDEAL EXCESS NOISE FACTOR, IT OUTPERFORMS EITHER KIND OF PHOTODETECTOR. THE HYBRID IS A CANDIDATE TO REPLACE PHOTOMULTIPLIERS IN THE READOUT OF LARGE CALORIMETERS IN FUTURE HIGH ENERGY PHYSICS DETECTORS AT THE SUPERCONDUCTING SUPER COLLIDER (SSC) AND ELSEWHERE. THE OBJECTIVE OF PHASE I IS TO DEMONSTRATE THE FAST RESPONSE AND LOW EXCESS NOISE CHARACTERISTICS OF THE HYBRID PHOTODETECTOR. THE PHASE II OBJECTIVE IS TO RESOLVE ALL TECHNICAL ISSUES AND DEMONSTRATE PROTOTYPES READY FOR COMMERCIAL MANUFACTURE.