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"Ultrafast Nonlinear Optics in the Mid-Infrared"

Dr. Aleksei Zheltikov
Texas A&M University


Recent impressive progress in the generation of high-power ultrashort pulses in the mid-infrared opens new horizons in ultrafast optical science and technologies, allowing the generation of unprecedentedly broad high-harmonic spectra, revealing unusual phenomena and unexpected properties of materials in the mid-infrared range, and promising new, unprecedented opportunities for laser-filamentation-assisted long-range transmission of high-power laser radiation and standoff detection. With the critical power of self-focusing scaling as the laser wavelength squared, a longer-wavelength driver would radically increase the peak power and, hence, the laser energy in a single laser filament in the atmospheric air. The search for such drivers has been ongoing over two decades, during which time the available laser sources limited filamentation experiments in the atmosphere to the near-infrared and visible ranges. In our experiments, filamentation of ultrashort mid-infrared pulses in the atmosphere has been demonstrated for the first time. With the spectrum of a femtosecond laser driver centered at 3.9 microns, right at the edge of the atmospheric transmission window, radiation energies above 20 mJ and peak powers in excess of 200 GW can be transmitted, as our experiments show, through the atmosphere in a single filament. Our studies reveal unique properties of mid-infrared filaments, where the generation of powerful mid-infrared supercontinuum is accompanied by unusual scenarios of optical harmonic generation, giving rise to remarkably broad radiation spectra, stretching from the visible to the mid-infrared. For mid-infrared field waveforms of much lower intensities, a physical scenario whereby freely propagating mid-infrared pulses can be compressed to pulse widths close to the field cycle has been identified. Generation of tunable few-cycle pulses in the wavelength range from 4.2 to 6.8 microns is demonstrated at a 1-kHz repetition rate through self-focusing-assisted spectral broadening in a normally dispersive, highly nonlinear semiconductor material, followed by pulse compression in the regime of anomalous dispersion, where the dispersion-induced phase shift is finely tuned by adjusting the overall thickness of anomalously dispersive components. Sub-two-cycle pulses with a peak power up to 60 MW are generated in the range of central wavelengths tunable from 5.9 to 6.3 microns.

Thursday, October 16, 2014
IQSE 578, 2:00 p.m.
Mitchell Physics Building

Institute for Quantum Science and Engineering
Texas A&M University

(Coffee and Cookies to be served 15 minutes prior start time)

Host: Dr. Marlan Scully