Frequency tunable superflash based on an electromagnetically induced transparency (EIT).

We present a new controllable superflash, a maximum transient peak at the falling edge of a square pulse, using a three-level electromagnetically induced transparency (EIT). The superflash in a two-level system occurs at a certain value of the detuning of the probe laser (Δ) when the optical depth (OD) of the medium is sufficiently large and constant. Here, we show the external tunability of the Δ for obtaining the maximum transient peak by introducing a three-level EIT. Owing to the EIT dispersion properties, we effectively tune the phase of the forward-scattered light (E) by externally controlling the EIT coupling light intensities associated with the Rabi frequency (Ω). When the incident light is turned off, the total transmitted field (E) experiences an out-of-phase shift, producing a peak intensity that is three times higher than the input. We observe that this new class of superflash (Type II) occurs near the EIT window and exhibits inverse-linearity of the OD, which is in contrast with the characteristics of the previously reported two-level superflash (Type I). Furthermore, we find the quadratic nature of tunability in Δ(Ω).The new tunability of the superflash by the Rabi frequency may facilitate more rapid and effective control of the superflash compared to a passive optical medium.