Incom, Inc. is now producing commercially available Large Area Picosecond Photo-Detectors (LAPPD™) usable in applications by early adopters. The first generation LAPPD™ is an all-glass 230 x 220 x 22 mm3 flat panel photodetector with a chevron stack of glass capillary array microchannel plates functionalized by atomic layer deposition, a semitransparent bi-alkali photocathode, and a strip-line anode. The photodetector is being optimized for applications requiring picosecond timing and millimeter spatial resolution and has achieved single photoelectron (PE) timing resolutions of α≤52 ps. Typical performance metrics include electron gains of 107 at 1 kV per MCP, low dark noise rates (15-30 Hz/cm2 at moderate gains), single PE spatial response along and across strips of 1.8 mm and 0.76 mm respectively and quantum efficiencies that are typically ≥20% at 365 nm. Changes to the “baseline” LAPPD™ are under development to optimize the photodetector for applications requiring very high spatial resolutions.
In proton therapy treatment, proton residual energy after transmission through the treatment target may be determined by measuring sub-relativistic transmitted proton time-of-flight velocity and hence the residual energy. We have begun developing this method by conducting proton beam tests using Large Area Picosecond Photon Detectors (LAPPDs) which we have been developing for High Energy and Nuclear Physics Applications. LAPPDs are 20cm x 20cm area Micro Channel Plate Photomultiplier Tubes (MCP-PMTs) with millimeter-scale spatial resolution, good quantum efficiency and outstanding timing resolution of ≤70 picoseconds rms for single photoelectrons. We have constructed a time-of-flight telescope using a pair of LAPPDs at 10 cm separation, and have carried out our first tests of this telescope at the Massachusetts General Hospital's Francis Burr Proton Therapy Center. Treatment protons are sub-relativistic, so precise timing resolution can be combined with paired imaging detectors in a compact configuration while still yielding high accuracy in proton residual energy measurements through proton velocity determination from nearly monoenergetic protons. This can be done either for proton bunches or for individual protons. Tests were performed both in "ionization mode" using only the Microchannel Plates to detect the proton bunch structure and also in "photodetection mode" using nanosecond-decay-time quenched plastic scintillators to excite the photocathode within each of the paired LAPPDs. Data acquisition was performed using a remotely operated oscilloscope in our first beam test, and using 5Gsps DRS4 Evaluation Board waveform digitizers in our second test, in each case reading out both ends of single microstrips from among the 30 within an LAPPD. First results for this method and future plans are presented.