Electromagnetically induced transparency: Propagation dynamics.

Electromagnetically induced transparency (EIT) is a process where one laser (or electromagnetic field) is used to modify the absorption coefficient and refractive index seen by a probe laser, thereby allowing it to propagate in what would otherwise be an optically thick medium. Early experimental observations have focused on the total transmission of a weak probe laser [1]. More recent work has focused on such topics as the dispersive properties of EIT [2,3], matched pulse generation [4], normal modes [5], dressed field states [6] and adiabatons [7], spatial consequences of EIT [8], and extensions of these effects to the continuum [9] and to detuned multistate systems [10]. There has also been substantial work on closely related topics such as applications to lasers without inversion [11] and to nonlinear optics [12]. In this work we report the first experimental studies of the temporal dynamics and spatial behavior of propagating EIT pulses. We probe a resonant transition which, without the “coupling” laser applied, has an absorption coefficient of a ­ 600ycm over a length of L ­ 10 cm saL ­ 6000d. For a weak probe and strong coupling laser, we observe group velocities as slow as cy165 with an energy transmission of 55%. For a strong probe laser we observe reshaping of both the coupling and probe laser pulses and the formation of propagating pulse pairs. Of perhaps most interest, we report the observation of nearly diffractionlimited beam transmission in a medium which, without the coupling laser present, is nearly optically impenetrable. We work with 99.97% isotopically pure lead (Pb) vapor in a 10-cm-long sealed fused-silica side-arm cell at a typical density of 2 3 1014 atoms ycm. Figure 1 shows the pertinent states and transitions. The probe transition 6s26p2 P0 ! 6s26p7s P1 has a wavelength of 283 nm and an oscillator strength of gf ­ 0.2; the coupling laser transition is 6s26p2 P2 ! 6s26p7s P1 with a wavelength of 406 nm and gf ­ 0.7 [13]. The 406and 283-nm laser beams are obtained from independent frequency doubled and tripled Ti:sapphire laser systems operating near 811 and 805 nm, respectively. Each of these systems consists of a continuouswave external-cavity (Littman configuration) diode laser which seeds a Ti:sapphire ring laser. Each ring laser is pumped with an 8-ns-long pulse at 532 nm from separate