Electromagnetically induced transparency in N-level cascade schemes

We examine electromagnetically induced transparency (EIT) in cascade scheme s with N levels and N - 1 fields. We show that transparency effects are pre sent when N is odd and that destruction of EIT is present on line centre wh en N is even. We predict multiple dark resonances in such schemes due to mu ltiphoton EIT effects. By examining atomic rubidium we propose methods of a chieving such schemes by use of coupling rf fields into hyperfine levels. ( C) 2001 Published by Elsevier Science B.V.