We directly image terahertz waves generated by optical rectification of tilted-pulse-front optical pulses in LiNbO3. The terahertz generation efficiency is highest when the pump-pulse tilt angle is equal to the THz Cherenkov angle.

Terahertz time-domain spectroscopy is used to measure the temperature-dependent refractive index of heavy oils down to 80 K. Evidence for a glass transition is observed, providing insight into the viscosity-temperature behavior of heavy oils.

We investigate the terahertz dielectric properties of heavy oils as a function of temperature using terahertz time-domain spectroscopy. These results facilitate the study of temperature-dependent intermolecular interactions within heavy oils.

The transient absorption bleaching and velocity overshoot of photoexcited carriers in GaAs and Si have been observed by the intense few-circle terahertz (THz) probe pulse in the optical pump-terahertz probe (OPTP) configuration. The free-carrier THz nonlinearity is attributed to the transient electron redistribution in conduction band induced by the strong THz electric field component.

Nonlinear dynamics of free carriers in direct bandgap semiconductors at terahertz (THz) frequencies is studied using the intense few-cycle source available at the Advanced Laser Light Source (ALLS). Techniques such as Z-scan and optical-pump/THz-probe are employed to explore nonlinear interactions in an n-doped InGaAs thin film and a photoexcited GaAs sample, respectively. The physical mechanism that gives rise to such interactions is found to be intervalley scattering. A simple Drude-based mathematical model that incorporates the intervalley scattering process is developed and agrees well with the THz response of free carriers in semiconductors.

Nonlinear dynamics of free-carriers in direct bandgap semiconductors at terahertz (THz) frequencies is studied using intense few-cycle pulses. Techniques as Z-scan, THz-pump / THz-probe, and optical-pump/ THz-probe are employed to explore nonlinear interactions in both n-doped and photoexcited systems. The physical mechanism that gives rise to such interactions is found to be intervalley scattering.

Nonlinear dynamics of free-carriers in direct bandgap semiconductors at terahertz (THz) frequencies is studied using high power, few-cycle pulses. The physical mechanisms that give rise to such dynamics will be discussed in details.

Nonlinear transient absorption bleaching of intense few-cycle terahertz (THz) pulses is observed in photoexcited GaAs using opticalpump--THz-probe techniques. A simple model of the electron transport dynamics shows that the observed nonlinear response is due to THz-electric- field-induced intervalley scattering over sub-picosecond time scales as well as an increase in the intravalley scattering rate attributed to carrier heating. Furthermore, the nonlinear nature of the THz pulse transmission at high peak fields leads to a measured terahertz conductivity in the photoexcited GaAs that deviates significantly from the Drude behavior observed at low THz fields, emphasizing the need to explore nonlinear THz pulse interactions with materials in the time domain.

We have performed open-aperture Z-scan measurements on n-doped InGaAs using intense few-cycle terahertz pulses. We observe a significant bleaching of the terahertz pulse absorption attributed to terahertz-electric-field-induced intervalley carrier scattering.

We use an open-aperture Z-scan technique to show how intense few-cycle terahertz pulses can experience a nonlinear bleaching of absorption in an n-doped semiconductor due to terahertz-electric-field-driven intervalley scattering of electrons in the conduction band. Coherent detection of the transmitted terahertz pulse waveform also allows the nonlinear conductivity dynamics to be followed with sub-picosecond time resolution. Both the Z-scan and time-domain results are found to be in agreement with our theoretical analysis.

We report on terahertz pulse generation by optical rectification of intense femtosecond laser pulses in a large aperture ZnTe single-crystal wafer, and on the possible applications to nonlinear THz optics.