We report a different mechanism to generate x-ray transients by exploiting high-field nonperturbative subcarrier-wave coherent phenomena. The interaction of several-cycle optical pulses with a nonlinear material results in carrier-wave Rabi flopping that acts as an alternative source for x-ray generation.
By solving Maxwell's curl equations coupled to a two-level atom, a theoretical study of carrier-wave Rabi flopping of femtosecond optical pulses of only several carrier-cycles time duration is reported. For pulse areas of $2\ensuremath{\pi}$, the usual self-induced transparency regime is essentially recovered. However, for larger pulse areas, carrier-wave Rabi flopping occurs that manifests in local carrier reshaping and subsequently to the production of significantly higher spectral components on the propagating pulse. These new features are not predicted by employing the area theorem or a slowly-varying-envelope approximation for the amplitude and phase terms---which is the usual approach.
Summary form only. The development of high-intensity ultrashort optical pulses has lead to a number of fascinating nonlinear optical propagation studies including Rabi flopping, self-induced transparency, and photon echo, to name but a few. Common to the description of these effects, is that their propagation phenomena can be described quite adequately by employing the appropriate coupled matter-Maxwell equations within the slowly-varying-envelope approximation (SVEA), i.e., the envelopes of the electromagnetic field and polarization are assumed to vary little over an optical period and wavelength. However, for several-cycle optical pulses this approximation becomes seriously questionable.
We demonstrate the feasibility of strong (up to atomic fields) and supershort (few-femtosecond or even subfemtosecond) subcycle (nonoscillating) electromagnetic solitons [EM bubbles (EMB’s)] in a gas of two-level atoms as well as EMB’s and preionization shock waves in classically nonlinear atoms. We show that EMB’s can be generated by existing sources of radiation, including subpicosecond half-cycle pulses and short laser pulses. We investigate how EMB characteristics are controlled by those of originating pulses. Our most recent results are focused on related transient phenomena, including EMB formation length, multibubble generation, and shocklike waves.
The ready availability of sub-picosecond pulses from mode locked lasers has led to a large number of experiments being performed on the coherent interaction between light and extended electronic states in semiconductors and semiconductor heterostructures [1]. In tandem with these experimental efforts the theoretical understanding of these phenomena has also made significant strides [2]. However, one theoretical prediction which has not been directly experimentally observed is the phenomenon of Rabi-flopping in semiconductors [3]. Rabi-flopping is the oscillation of the excited state population induced by a strong light field. Here we present experimental results based on the nonlinear interaction of two copropagating pulses and show that in the theoretical treatment the observed behavior arises from the occurrence of a Rabi flop.
Recently, a dependence of Rabi flopping on the carrier-envelope phase of the exciting laser pulses was predicted theoretically [Phys. Rev. Lett. 89, 127401 (2002)] for excitation of a thin semiconductor film with intense few-cycle pulses. Here, we report corresponding experiments on 50-100-nm thin GaAs films excited with 5-fs pulses. We find a dependence on the carrier-envelope phase arising from the interference of sidebands from the fundamental or the third-harmonic Mollow triplet, respectively, with surface second-harmonic generation.