Coherent Population Trapping Induced by Phase Modulated and Fluctuating Fields

We examine the effects of cross correlated phase fluctuations on the coherent population trapping （CPT） induced by a pair of phase-modulated fields with equal modulation frequencies in a three-level A system. The maximal coherence of-0.5, which appears when CPT occurs for equal modulation indices, is preserved in the presence of the critically cross-correlated fluctuations. Unexpectedly, the non-maximal coherence, which is established when CPT is obtained for different modulation indices, is significantly enhanced due to the critically cross-correlated fluctuations.