A secondary emission detector capable of preventing detection of the photoelectric effect induced by pulsed lasers

Abstract

A secondary emission detector for neutral particles has been constructed. The detector is designed for an experiment to investigate the photodetachment process X-+h nu to X+e- where X- can be any negative ion. A beam of negatively charged ions is merged with a laser beam, and the rate of the photodetachment process is measured by monitoring the neutral atom production. The neutral atoms impinge on a coated glass plate where secondary electrons are formed which are detected with a channel electron multiplier. The laser beam strikes the glass plate at the same point as the neutral atoms do and the intense laser light produces electrons by the photoelectric effect. This gives rise to an unwanted signal which is much stronger than the desired signal induced by the neutral atoms. The neutral particle detector described is capable of preventing the detection of electrons produced by the photoelectric effect. It is shown that the detection of electrons produced by the light from pulsed lasers with pulse energies of up to 10 mJ and wavelengths down to 250 nm can be completely prevented without any decrease in the yield of the electrons produced by the neutral atoms. The detection efficiency of neutral atoms with an energy of 3 keV is shown to be 40%.