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We study nonlinear THz effects in photoexcited gated graphene, using optical-pump/Zwtewse-THz-probe spectroscopy. A crossover from negative to positive differential THz transmission has been observed at the lowest doping concentration when the THz field is increased. Using a simple Drude model of the graphene photoconductivity, we attributed the observed behavior to a transition from a domain in which...
Using optical-pump/THz-probe spectroscopy on gated, undoped graphene, we find that as the amplitude of the THz probe is increased, we observe a cross-over from optically-induced transmission decrease to increase.
Terahertz field-induced transmission enhancement in monolayer epitaxial graphene is observed with increasing terahertz field. Photoexcitation leads to further transmission enhancement that is found to be less for the higher terahertz field amplitudes.
We investigate the terahertz generation efficiency dependence as function of the pulse width durations at 800 nm. Our results confirmed conversion efficiency of 0.35% with saturation at 240 fs of pulse width duration.
We report temperature dependence and thermal hysteresis behavior of terahertz transmission through photoexcited graphene. We vary the temperature between room temperature and 1800°C, and use the optical-pump/terahertz-probe differential transmission technique.
We present nonlinear effects induced by an intense terahertz field on the transmission response of metamaterial structures fabricated on silicon wafer, as well as ultrafast modulation in the terahertz response of our devices.
We present optical pump / high-power THz probe measurements for undoped silicon at different optical pump fluences. We observe an absorption bleaching of intense terahertz (THz) pulses, which decreases with increasing optical pump fluence.
We present our investigation on the THz space-time emission characteristic induced by the non-paraxial generation regime in highly localized THz generation via optical rectification on sub-wavelength areas.
We investigate Terahertz (THz) radiation from a ZnSe large aperture photoconductive antenna (LAPCA). The saturation fluence is seen to be significantly different for above and below band-gap excitation, and in comparison to GaAs substrates, shows strong potential as a high-power THz emitter.
The nonlinear interaction of intense few-cycle terahertz pulses with free carriers in semiconductors is studied in both n-doped and photoexcited systems. Intervalley scattering is found to cause ultrafast modulation and bleaching of the terahertz absorption.
We demonstrate, for the first time, high-order harmonic generation from C60 pumped by intense femtosecond Ti: sapphire laser. Laser-produced plasmas from C60-rich epoxy and C60 films were used as the nonlinear media. Harmonics up to the 19th order were observed. The harmonic yield from fullerene-rich plasma is about 25 times larger compared with those produced from bulk carbon target.
We demonstrate high-order harmonic generation from C60 fullerenes pumped by intense Ti:sapphire laser. We observe a 25 times increase in the harmonic yield compared with bulk carbon, near the 22 eV giant resonance of C60.
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