Virtual image replay system for viewing bubble chamber holograms

A virtual image replay system has been constructed at the Fermi National Accelerator Laboratory to replay holograms produced in experiment E-632. The holograms were produced by a modified in-line holographic system installed in the 15 ft. bubble chamber detector. The experiment produced 110,000 holograms useful for physics analysis. The holograms were recorded on 70 mm Agfa-Gevaert Holotest 10E75 film. The bubble images represent tracks of charged particles produced from high energy neutrino interactions. Since one of the main purposes of the experiment was to observe short lived particles, our holographic system makes it possible to record smaller bubble images (approximately 100 mm) than possible with conventional photographs (approximately 500 mm) which record the entire visible chamber volume (28 m 3 ) and are subject to the limitations of conventional photography i.e., diffraction of the camera lens aperture. Although the holographic volume is 1.5 m 3 , 20 - 30% of all the interactions in the bubble chamber fall within the holographic volume since the beam is concentrated in the center of the chamber. An important aspect of the experiment is the inspection of the holograms and for this reason an effective replay system is necessary. We have constructed a low cost replay system and chosen a virtual image replay because it requires much less laser power and this has proven to be a great advantage. We discuss the major components of the holographic replay machine and the relevant design features. Replay wavelengths different than the original recording wavelength are possible and corrected for in the system described. The resolution of the system is improved using a liquid film gate. A fiber optic reconstruction reference beam has been useful and convenient. Examples of replayed bubble chamber events are shown.