4-GHZ INTERNAL MCP-PHOTOMULTIPLIER CROSS-CORRELATION

We have performed sinusoidal and pulsed internal cross correlation within a Hamamatsu model R2024U gatable microchannel-plate photomultiplier (MCP-PMT) by biasing and modulating the gating mesh which is located 0.2 mm behind the photocathode. The light source used was a sync-pumped and cavity-dumped dye laser. Near the photocathode center, no effective high-frequency photocurrent modulation was achieved. However, for a circular area near the photocathode edge, useful modulation up to 4.5 GHz, the frequency limit of our amplifier, was obtained. The modulation frequency response is characterized by resonances caused by the gating mesh which represents a strong disturbance with respect to the modulation-cable termination. The shortest measured rise time for pulsed modulation was 178 ps at 700 nm. The measured pulse response is a "mirror image" of a response curve as observed normally because the gating pulse is sampled by the δ-like photoelectron pulse. From this observation it can be reasoned that an even higher gating speed seems to be feasible by using a better mesh construction. We have utilized the internally cross-correlated R2024U to perform frequency-domain fluorometry test measurements. Using etalon glass plates instead of fluorescent samples, delay times as short as 6 ps have been measured with an accuracy of 1 ps.