Rapid passage signals induced by chirped quantum cascade laser radiation: K state dependent-delay effects in the nu(2) band of NH3

In this Letter, a 10 mu m quantum cascade laser operating in the intrapulse mode is used observe rapid passage (RP) effects within a 40 cm single-pass gas cell containing low pressures of NH3. The laser tuning range allows the rotational states J = 2 with K = 0, 1, and 2 to be probed. We show that the RP structures change as a function of optical density and that the magnitude of the delay in the switch from absorption to emission as a function of increased gas pressure is dependent upon the initial value of K. These measurements are qualitatively well modeled using the Maxwell-Bloch equations.