Pulse propagation in a medium optically dressed by a phase-modulated   field
  Pulse propagation is studied in an EIT medium with the control field having a periodically varying phase (chirp). Based both on numerical calculations and on an approximate approach neglecting absorption and nonadiabatic effects, it is shown that transparency occurs for probe pulses having a sufficiently narrow envelope and an appropriately suited chirp. For other chirped pulses the evolution of their spectra along a sample is studied. Using a projection method one can divide a pulse into a part for which the medium is transparent and a rest for which it is opaque. 
Andrzej Raczynski, Jaroslaw Zaremba, and Sylwia Zielinska-Raczynska
quant-ph physics.optics