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_peak) when the optical depth (OD) of the medium is sufficiently large and constant. Here, we show the external tunability of the Δ_peak 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_s) by externally controlling the EIT coupling light intensities associated with the Rabi frequency (Ω_c). When the incident light is turned off, the total transmitted field (E_t) 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_peak(Ω_c).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.