Coherent population trapping and the effect of laser phase fluctuations

Some of the essential conditions for coherent trapping and laser phase fluctuations are described, with reference to three prototypical laser systems: spontaneous emission from two identical two-level atoms; a lambda system coupled to two lasers (excited and nonexcited); and a ladder system coupled to two lasers (excited and nonexcited, respectively). A series of equations are derived which express the laser bandwidth factors, atomic state populations, fluorescence spectra and coherent trapping for each prototype device. A schematic outline is presented of the characteristic Ramsey fringes in the fluorescence spectrum in a sodium lambda laser system.