PT Journal AU Shelkovnikov, A Grain, C Nguyen, CT Butcher, RJ Amy-Klein, A Chardonnet, C TI 500-Hz two-photon Ramsey fringes with a SF[sub:6] beam: towards a new frequency standard in the 30-THz spectral region SO Applied Physics B: Lasers and Optics JI Appl. Phys. B: Lasers and Optics PY 2001 BP 93 EP 98 VL 73 DE THz applications ER