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 $J=1\mathrm{}\Rightarrow 1$ transition at $\lambda =1.083\mathrm{}$ μm. These states are characterized by two peaks in the atomic momentum distribution at $\pm Q\hslash k(Q=\mathrm{positive}\mathrm{integer})$, where $k$ is the magnitude of the optical wave vector. VSCPT states previously observed are characterized by $Q=1\mathrm{}$, but we have observed long-lived states with $Q=2\mathrm{}$. Optical Bloch equation calculations show that these high-velocity dark states appear at higher $Q$ for greater light intensity.

• Received 24 July 1995

DOI:https://doi.org/10.1103/PhysRevA.53.946