An electronic shutter for holographic applications.
Precise control of exposure is generally required in holography and optical spatial filtering. The experimental results of Friesem et al. show that, for Kodak 649-F film, the diffraction efficiency changes rapidly with small changes in bias because of the high contrast nature of the emulsion. For example, the maximum allowable change in bias is about one half stop on either side of the optimum value. Even over this restricted range, the diffraction efficiency at the extremes is only one-third the maxi­ mum value. In the past, holographic exposures of many seconds were not uncommon, and exposure control was relatively simple without recourse to mechanical shutters. With the advent of more powerful lasers and of faster high resolution emulsions such as Agfa-Gevaert Scientia 14C70, exposure times have been signifi­ cantly reduced. Standard, readily available mechanical shutters are largely inadequate because fine exposure control between the fixed stops is not generally possible. In this letter, we describe an electronic shutter suitable for the described application, which provides continuously variable exposure times in the range from 1 msec to many seconds.