Ka Lo Yeh

Generation of high-power terahertz pulses by tilted-pulse-front excitation and their application possibilities

The principles and most-recent results of high-power THz generation through optical rectification using a tilted optical pulse front are described. Single-cycle THz pulses of multimicrojoule energies are generated at kHz repetition rates, and average THz power levels exceeding 1 mW can be generated at kHz-MHz repetition rates. Applications in nonlinear THz spectroscopy and THz coherent control are discussed.

Impact ionization in InSb probed by terahertz pump—terahertz probe spectroscopy

Indium antimonide InSb is a model system for the study of hot-electron dynamics due to its low band gap of 170 meV at room temperature 1 and the fact that it has the highest electron mobility and saturation velocity among all known semiconductors. The wealth of nonequilibrium transport phenomena that have been observed in this material 2–4 is of special interest due to the large nonparabolicity of the conduction band, 5 which results in negative differential mobility

Efficient terahertz generation by optical rectification at 1035 nm

We demonstrate efficient generation of THz pulses by optical rectification of 1.03 um wavelength laser pulses in LiNbO3 using tilted pulse front excitation for velocity matching between the optical and THz fields. Pulse energies of 100 nJ with a spectral bandwidth of up to 2.5 THz were obtained at a pump energy of 400 uJ and 300 fs pulse duration. This conversion efficiency of 2.5x10(-4) was an order of magnitude higher than that obtained with collinear optical recitification in GaP, and far higher still than that measured using ZnTe in an optimized geometry. Using a simple model we demonstrate that two- and three-photon absorption strongly limit the THz generation efficiency at high pump fluences in ZnTe and GaP.

Observation of nonequilibrium carrier distribution in Ge, Si, and GaAs by terahertz pump-terahertz probe measurements

We compare the observed strong saturation of the free-carrier absorption in

THz-pump/THz-probe spectroscopy of semiconductors at high field strengths [Invited]

n

Fiber laser pumped high average power single-cycle terahertz pulse source

-type semiconductors at 300 K in the terahertz (THz) frequency range when single-cycle pulses with intensities up to

Impact ionization in InSb studied by THz-pump-THz probe spectroscopy

150text{ }text{MW}/{text{cm}}^{2}

Terahertz death ray

are used. In the case of germanium, a small increase in the absorption occurs at intermediate THz pulse energies. The recovery of the free-carrier absorption was monitored by time-resolved THz pumpchar21{}THz probe measurements. At short probe delay times, the frequency response of germanium cannot be fitted by the Drude model. We attribute these unique phenomena of Ge to dynamical overpopulation of the high mobility

TERAHERTZ POLARITONICS: HIGH POWER THZ SIGNAL GENERATION IN FERROELECTRIC CRYSTALS

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Generation of high average power 1 kHz shaped THz pulses via optical rectification

conduction-band valley.