Ultraslow light propagation in an inhomogeneously broadened rare-earth   ion-doped crystal
  We show that Coherent Population Oscillations effect allows to burn a narrow spectral hole (26Hz) within the homogeneous absorption line of the optical transition of an Erbium ion-doped crystal. The large dispersion of the index of refraction associated with this hole permits to achieve a group velocity as low as 2.7m/s with a ransmission of 40%. We especially benefit from the inhomogeneous absorption broadening of the ions to tune both the transmission coefficient, from 40% to 90%, and the light group velocity from 2.7m/s to 100m/s. 
Elisa Baldit (LPN), Kamel Bencheikh (LPN), Paul Monnier (LPN), Juan   Ariel Levenson (LPN), Vincent Rouget (LPN)