Stacked Optical Precursors from Amplitude and Phase Modulations

We report the generation of stacked optical precursors from a laser beam whose amplitude or phase is modulated by sequenced on-off step waveforms. Making use of the constructive interference between the precursors produced from different steps, as well as the main field, we generate optical transient pulses having peak powers of eight times the input power with electromagnetically induced transparency in laser-cooled atoms.

Figure 1

System schematics for generating stacked optical precursors. (a) ${}^{85}\mathrm{Rb}$ energy level diagram of a three-level EIT system. (b) Experimental setup. In the presence of a strong coupling laser (${\omega }_c$) and a weak probe laser beam (${\omega }_p$), whose amplitude or phase is modulated by electro-optical modulator (EOM), propagates through a cold ${}^{85}\mathrm{Rb}$ atom cloud prepared in a magneto-optical trap (MOT), and is detected by a photon-multiplier tube (PMT).

Figure 2

Generation of stacked optical precursors from amplitude modulation. Transmission of a weak probe pulse with sequenced on-off step amplitude modulation is shown in (a) the two-level system (coupling Rabi frequency ${\Omega }_c=0$) and (b) EIT system (${\Omega }_c=2.5{\gamma }_{13}$) with optical depth ${\alpha }_{0}L=33$. Panel (c) is the applied amplitude-modulation waveform.

Figure 3

Generation of stacked optical precursors from phase modulation. Transmission of a weak probe pulse with sequenced on-off step phase modulation is shown in (a) the two-level system (${\Omega }_c=0$) and (b) EIT system (${\Omega }_c=2.5{\gamma }_{13}$) with optical depth ${\alpha }_{0}L=33$. Panel (c) is the applied phase-modulation waveform.

Figure 4

The normalized transient peak intensity as a function of the finite rise time in the EIT system from phase modulation. For ${\alpha }_{0}L=66$, the coupling Rabi frequency (${\Omega }_c$) is adjusted to have the same main field transmission (80%) as that at ${\alpha }_{0}L=33$.