Extreme Nonlinear Optics in Semiconductors
In traditional nonlinear optics, the absolute changes of the optical properties are tiny if one follows them versus time on a timescale of a cycle of light (e.g., 2.9 fs for the GaAs band gap). This simple fact is the basis of many concepts and approximations of traditional nonlinear optics. Today, about 40 years after the invention of the laser, the shortest optical pulses generated are about 1.5 cycles of light in duration. This comes close to the ultimate limit of a single optical cycle. In our own experiments described below, we employ two-cycle (5 fs) pulses. Moreover, laser pulses with peak intensities around 1013 W/cm2 are available directly from mode-locked laser oscillators. Under these conditions, one has substantial or even extreme changes of the optical properties on the timescale of a cycle of light. In general, one can say that whenever an energy associated to the light intensity becomes comparable to or even larger than a characteristic energy of the material or system under investigation, the laws of traditional nonlinear optics fail and something new is expected to happen. We want to call this regime extreme nonlinear optics or carrier-wave nonlinear optics. For the special case of resonant interband semiconductor optics, it is entered if the Rabi energy becomes comparable to the carrier photon energy.
KeywordsRabi Frequency Bloch Vector Spectrometer Frequency Keldysh Parameter Laser Electric Field
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