Abstract-Sub-cycle control of terahertz high-harmonic generation by dynamical Bloch oscillations

• O. Schubert,
• M. Hohenleutner,
• F. Langer,
• B. Urbanek,
• C. Lange,
• U. Huttner,
• D. Golde,
• T. Meier,
• M. Kira,
• S. W. Koch
• & R. Huber
• • http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2013.349.html

Ultrafast charge transport in strongly biased semiconductors is at the heart of high-speed electronics, electro-optics and fundamental solid-state physics^{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13}. Intense light pulses in the terahertz spectral range have opened fascinating vistas^{14, 15, 16, 17, 18,19, 20, 21}. Because terahertz photon energies are far below typical electronic interband resonances, a stable electromagnetic waveform may serve as a precisely adjustable bias^{5, 11, 17, 19}. Novel quantum phenomena have been anticipated for terahertz amplitudes, reaching atomic field strengths^8, 9, 10. We exploit controlled (multi-)terahertz waveforms with peak fields of 72 MV cm⁻¹ to drive coherent interband polarization combined with dynamical Bloch oscillations in semiconducting gallium selenide. These dynamics entail the emission of phase-stable high-harmonic transients, covering the entire terahertz-to-visible spectral domain between 0.1 and 675 THz. Quantum interference of different ionization paths of accelerated charge carriers is controlled via the waveform of the driving field and explained by a quantum theory of inter- and intraband dynamics. Our results pave the way towards all-coherent terahertz-rate electronic