HETERODYNE OPTICAL PHASE-LOCKING OF EXTENDED-CAVITY SEMICONDUCTOR-LASERS AT 9 GHZ

In order to stimulate atomic velocity-selective Raman transitions on the 852 nm caesium D-2 line in an atomic fountain clock, two extended-cavity diode lasers have been optically phase-locked at a frequency offset of 9.192 GHz, The measured linewidth (fwhm) of the free-running lasers is 50 kHz. The phase-locked loop bandwidth, evaluated by observing the frequency noise spectrum, is 3.7 MHz and the phase error variance is found to be no more than 4X10(-3) rad(2).