Decoherence Times of Rabi Oscillations in Micro-Plasmas

Daniel N. Rogovin

Stefano Olivares Rodolfo Bonifacio

Ryan Compton, A. I. Filin, Dmitri Romanov +1 more

Broadband, coherent radiation in the optical frequency range is generated using micro-plasma channels in atmospheric gases in a pump-probe experiment. A micro-plasma medium is created in a gas by a focused intense femtosecond pump pulse. A picosecond probe pulse then interacts with this micro-plasma channel, producing broad, coherent sidebands that are associated with luminescence lines and are red- and blue-shifted with respect to the laser carrier frequency. These sidebands originate from the induced Rabi oscillations between pairs of excited states that are coupled by the probe pulse. These excited states become populated in the process of plasma cooling. Thus, the sideband radiation intensity tracks the micro-plasma evolution. The sidebands incorporate Rabi shifts corresponding to varying value of the electric field magnitude in the probe pulse: this makes them broad and malleable to tuning. The intensity of the probe beam ~ 1010 W cm-2, creates a maximum sideband shift of> 90 meV from the carrier frequency, resulting in an effective bandwidth of 200 meV. The sidebands may be effectively controlled by the intensity and temporal profile of the probe pulse. The giant Rabi shift is both tunable and coherent over a wide range of frequencies and over a wide range of atomic transitions. The fact that the coherence is observed in a micro plasma demonstrates that Rabi cycling is possible at high temperature with moderately high laser intensities (1010 W cm-2) as long as transitions close to the driving frequency ( ~ 2 % c) are available.

Ryan Compton, A. I. Filin, Dmitri Romanov +2 more

A new coherent laser source arising from giant time-dependent generalized Rabi shifting has been demonstrated. A 1 ps laser is transformed into a pulse with bandwidth corresponding to a 70 fs pulse via time-dependent Rabi shifting.

Scott A. Holmstrom, Andrew S. M. Windsor, C. Wei +2 more

George Heck, A. I. Filin, Dmitri Romanov +1 more

Characteristic fringe patterns of spectral interference in dynamic Rabi sidebands are used as a means to investigate decoherence phenomena in a highly nonequilibrium underdense microplasma formed in atmospheric-pressure oxygen gas in the wake of a strong-field (\ensuremath{\sim}10${}^{13}$ W/cm${}^{2}$) femtosecond pump pulse. The same transient processes in the nonequilibrium plasma work both to create the effective two-level systems producing coherent sidebands and to destroy the coherence and smear the sideband spectral structure; the observed spectral fringe pattern is a result of the trade-off of these two effects. The sidebands generated on a moderately intense (\ensuremath{\sim}10${}^{10}$ W/cm${}^{2}$) picosecond laser pulse reveal the decoherence rate as a function of the pump-pulse intensity and the pump-probe delay time. The rate increases with the pump laser intensity and decreases with the delay with corresponding decoherence times in the range of 750 fs to 3 ps, in good agreement with theory revealing that electron scattering dominates the dynamics for the subnanosecond relaxation processes.