A HIGH PERFORMANCE SPOT SIZE MONITOR*

Beam size estimates made using beam-beam deflections are used for optimization of the Stanford Linear Collider (SLC) electron-positron beam sizes. Beam size and intensity goals for 1996 were 2.1 x 0.6 m m (x,y) at 4.0x10 10 particles per pulse. Conventional profile monitors, such as scanning wires, fail at charge densities well below this. Since the beam-beam deflection does not provide single beam information, another method is needed for Interaction Region (IP) beam size optimization. The laser based profile monitor uses a finely focused 349 nm. wavelength, frequency-tripled YLF laser pulse that traverses the particle beam path about 29 cm away from the e+/e- IP. Compton scattered photons and energy degraded e+/e- are detected as the beam is steered across the laser pulse. The laser pulse has a transverse size, ( s 0,), of 380 nm and a Rayleigh range of about 5 m m. This is adequate for present or planned SLC beams. Design and results are presented