Experiments of nanometer spot size monitor at FFTB using laser interferometry

The nanometer spot size monitor based on laser interferometry has been developed and installed in the Final Focus Test Beam (FFTB) line at SLAC. The beam experiments started in September 1993, the first fringe pattern from the monitor was observed in the beginning of April 1994, then the small vertical spot around 70 nm was observed in May 1994. The spot size monitor has been routinely used for tuning the beam optics in FFTB. The basic principle of this monitor has been well proved, and its high performance as a precise beam monitor in the nanometer range has been demonstrated.