Abstract

Liquid helium has intrigued the physicists for more than eighty years. Despite the fact that fluid and superfluid helium have been used over many decades world-wide in connection with basic research and also with applications, no microscopic theories have been presented so far which can explain all the different properties of liquid helium. An early approach to extend the knowledge on this topic was the use of single electrons and He⁺ ions as microprobes in the liquid. Since the optical spectra of these species are located in a wavelength region hardly accessible for the common optical methods predominantly drift experiments have been carried out.

© 1996 Optical Society of America