  Laser guide star systems based on Rayleigh scattering require some means to
deal with the flash of low altitude laser light that follows immediately after
each laser pulse. These systems also need a fast shutter to isolate the high
altitude portion of the focused laser beam to make it appear star-like to the
wavefront sensor. We describe how these tasks are accomplished with UnISIS, the
Rayleigh laser guided adaptive optics system at the Mt. Wilson Observatory
2.5-m telescope. We use several methods: a 10,000 RPM rotating disk, dichroics,
a fast sweep and clear mode of the CCD readout electronics on a 10 $\mu$s
timescale, and a Pockel's cell shutter system. The Pockel's cell shutter would
be conventional in design if the laser light were naturally polarized, but the
UnISIS 351 nm laser is unpolarized. So we have designed and put into operation
a dual Pockel's cell shutter in a unique bow tie arrangement.
