High-velocity dark states in velocity-selective coherent population trapping

We have observed long-lived dark states in velocity-selective coherent population trapping (VSCPT) in a one-dimensional lin-angle-lin configuration with metastable He atoms using the [Formula Presented] transition at [Formula Presented] μm. These states are characterized by two peaks in the atomic momentum distribution at [Formula Presented], where [Formula Presented] is the magnitude of the optical wave vector. VSCPT states previously observed are characterized by [Formula Presented], but we have observed long-lived states with [Formula Presented]. Optical Bloch equation calculations show that these high-velocity dark states appear at higher [Formula Presented] for greater light intensity.