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Photo-electron emission directly in superfluid helium
Despite the fact that electron transport in condensed helium has been studied for
over half a century [1], observations of new intriguing effects still appear [2]. Alas, the traditional
methods of injecting electrons into condensed helium (radioactive-sources, electrical discharge
or field emission) lead to generation of helium ions, recombination of which is accompanied by
emergence of a large number of excitations. As a result, interpretation of such experiments is
not simple and sometimes may be questionable. In this respect, photoelectron emitters, which
operate with energies substantially smaller than the ionization energy of helium, are preferable.
However, immersion of the photocathode into condensed helium suppresses electron emission.
Nevertheless, we managed to achieve electron currents (>20 fA) with the In photocathode
immersed directly in liquid superfluid helium. The UV light (λ=254 nm) was guided to the
photocathode through a two-meter long Al-covered quartz optical fiber.