Laser beams as fiducial lines in bubble chambers

It is proposed to base the fiduciary system of large volume bubble chambers on laser beams originating from theodolite-fixed positions and thus traversing the liquid at well defined space coordinates. From a series of experiments some important conditions for this proposal have been established: Rayleigh-scattering on molecular concentration fluctuations in the chamber liquid is responsible for the visibility of laser beams which can be photographed under angles up to 90° within reasonable exposures. Small-angle random deflections of the laser beam were observed which are due to thermal turbulence in the chamber liquid and yield a rms net deflection angle of ± 0.075 mrad/m12. This error in angular position is about one order of magnitude smaller than that caused by multiple Coulomb scattering on the track of a 10 GeV particle.