Amplitude and Phase Dynamics of Superradiant and Raman Pulse Trains

Damien P. Scherrer, Fritz Kurt Kneubühl

豊 吉川

Sergei N Bagaev, A. A. Preobrazhenskaya, Nikolai A. Timofeev +7 more

Abstract For the first time, it is demonstrated that the magnitude and sign of the effect of “spectral condensation” of a laser pulse at the resonant-transition frequency of a dense medium can be controlled by changing the driving-pulse parameters (chirp, pulse width, and pulse amplitude). In the process of this, importantly, the driving-pulse energy and spectrum remain unchanged. Direct time-resolved measurements revealed an oscillatory character of the induced superradiance of rubidium vapors representing a long train of decaying short pulses. The width and repetition rate of the pulses in the train are determined by atomic density N0 of the medium, while the width of an entire superradiance pulse (10 ps) is considerably larger than that of the driving laser pulse (50 fs).

Yu, Huihui, Yuan Zhang, Gang Chen +1 more

Superradiant Raman scattering of Rubidium atoms has been explored in the experiment [Nature 484, 78 (2012)] to prove the concept of the superradiant laser, which attracts significant attentions in quantum metrology due to the expected ultra-narrow linewidth down to millihertz. To better understand the physics involved in this experiment, we have developed a quantum master equation theory by treating the Rubidium atoms as three-level systems, and coupling them with a dressed laser and an optical cavity. Our simulations show different superradiant Raman scattering pulses for the systems within the crossover and strong coupling regime, and the shifted and broader spectrum of the steady-state Raman scattering. Thus, our studies provide a unified view on the superradiant Raman scattering pulses, and an alternative explanation to the broad spectrum of the steady-state Raman scattering, as observed in the experiment. In future, our theory can be readily applied to study other interesting phenomena relying on the superradiant Raman scattering, such as magnetic field sensing, real-time tracking of quantum phase, Dicke phase transition of non-equilibrium dynamics and so on.

Martin P. van Exter, Ad Lagendijk

Albert T. Rosenberger, Ho Kyoon Chung, T. De Temple

Several polar molecules possessing strong far-infrared (FIR) transitions have been optically pumped by a mode-locked CO2TEA laser in a single-pass configuration. All the resulting FIR pulses are shorter than the sub-T2pump pulses; subnanosecond FIR pulses are observed. These short FIR pulses exhibit lethargic gain, stimulated Raman emission, and multiple-pulse superradiance. The experimental results are modeled by numerical solution of the Maxwell-density matrix equations for two fields interacting with a three-level system. Level degeneracy is included, and the pump is described by a multimode power spectrum with a parabolic envelope, resulting in a periodic train of pulses. Variation of the detuning of the pump from resonance allows simulation of the superradiant or Raman cases. This fully coherent model, which is the major contribution of this paper, explains key experimental observations such as the noncoincidence of the Raman peak with the pump modulation minimum and the enhancement of multiple-pulse superradiance due to remanent polarization.