  We demonstrate phase lock of two >1.6W Titanium:sapphire lasers with a phase
noise of -138dBc/Hz at 1MHz from the carrier, using an intra-cavity
electro-optic phase modulator. The residual phase variance is 2.5 10^(-8)rad^2
integrated from 1Hz to 10kHz. Instantaneous offset frequency steps of up to
4MHz are achieved within 200ns. Simultaneous atom interferometers can make full
use of this ultra-low phase noise in differential measurements by suppressing
common influences from vibration of optics.
