The performance of a new gaseous photodetector was investigated. It consist
s of a solid photocathode and a gas amplification structure of the MICROMEG
AS type. Using a mixture of helium and isobutane at atmospheric pressure, a
stable and high amplification gain close to 10(7) was achieved. Such a hig
h gain and small fluctuations allowed the detection of single photoelectron
s with a time resolution better than 700 ps. These performances are compara
ble with those obtained with the best photomultipliers. (C) 2000 Elsevier S
cience B.V. All rights reserved.