title: Liquid level interferometer.
abstract: An inexpensive field instrument has been built to measure changes in water level to an accuracy of lambda/8. A novel magnetic suspension is used to position the floating retroreflector of a laser interferometer. Direction sensing is achieved by dual optical channels phased near quadrature by means of an absorbing beam splitter.
authors.forename: S F
authors.initials: SF
authors.lastname: Jacobs
authors.forename: J G
authors.initials: JG
authors.lastname: Small