Observation of Broadband Time-Dependent Rabi Shifting in Microplasmas

Abstract

Coherent broadband radiation in the form of Rabi sidebands is observed when a ps probe laser propagates through a weakly ionized, electronically excited microplasma generated in the focus of an intense pump beam. The sidebands arise from the interaction of the probe beam with pairs of excited states of a constituent neutral atom via the probe-induced Rabi oscillation. Sideband shifting of >90 meV from the probe carrier frequency results in an effective bandwidth of 200 meV. The sidebands are controlled by the intensity and temporal profile of the probe pulse; with amplitude and shift in agreement with the predictions of a time-dependent generalized Rabi cycling model.

Dynamic Rabi sidebands in laser-generated microplasmas: Tunability and control

“…As a result of the interaction of a probe beam with the oxygen plasma, the blueshifted and redshifted sidebands emerge in the spectrum, as reported in Ref. [7]. With a 1.05-mW probe, the intense blue-side broadband emission is centered on 1.643 eV.…”

“…These underdense plasmas (wherein the plasma frequency is smaller than the carrier frequency of a typical laser beam) are transparent and can be probed by weaker laser pulses, carrying the promise of linear and nonlinear optical effects. In particular, gas-component specific dynamic Rabi oscillations have been recently observed [7]. The phenomenon is marked by the generation of broad coherent sidebands and, remarkably, was observed despite plasma electron temperatures on the order of 1 eV [1,2], where collisional dephasing might be expected to squelch any coherence.…”

“…When the carrier frequency ω c of a probe laser pulse is nearly resonant with any of these lines (with a detuning), the laser field couples with the corresponding transition and induces time-dependent Rabi oscillations in the effective two-level systems. We reported the observation of the resulting coherent broadband radiation in argon and oxygen using picosecond probe laser pulses [7]. The picosecond pulse duration provided a sufficiently short interaction time allowing Rabi cycling to compete with the electron-atom and atom-atom collisional dephasing mechanisms.…”

1-J white-light continuum from 100-TW laser pulses

“…This line may be the oxygen atomic multiplet OI(3p 5 P -3s 5 S) centered at 777.4 nm in the plasma generated in air by the filaments [24,25]. This line would subsequently be Rabi-shifted due to the high intensity, as recently observed by Compton et al [26]. The influence of the chirp could be understood by considering that the proposed process requires two steps: (i) the formation of excited atomic oxygen and (ii) the stimulation of the emission by the same incident pulse.…”

Dynamics of strong-field laser-induced microplasma formation in noble gases

“…As the plasma cooling evolution proceeds, the excited states corresponding to these transition lines become populated, leading to population inversion. [49] Then, the FWM signal induces stimulated emission from the excited state population in the observation window resulting in significant amplification. This scenario agrees well with the fact that the deviant Ne behavior emerges later in the process of the cooling evolution.…”