Terahertz pulse induced intervalley scattering in photoexcited GaAs

Abstract

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.

Intense ultrashort terahertz pulses: generation and applications

“…In all samples a strong drop in absorption is detected, with a subsequent recovery time on the order of a few picoseconds depending on the material. The dynamics can be described qualitatively by a simple model of the electron transport [121,22]. From the spectral analysis of the data (not shown) it can be seen that the characteristics of the hot electron gas deviates significantly from the Drude behavior and a better theoretical modeling taking into account the hot electron properties is needed.…”

“…Nonlinear transmission studies in combination with modeling of the contribution of several of these effects have been reported [118] and strong absorption bleaching has been observed in a number of n-type semiconductors such as GaAs [119], InGaAs [120], Ge, Si [22] as well as in photoexcited GaAs [121]. In bulk samples, the increase in terahertz transmission can be almost one order of magnitude, making these materials suitable for use as saturable THz absorbers at room temperature [97].…”

Diffraction-Limited High-Power Single-Cycle Terahertz Pulse Generation in Prism-Cut LiNbO3for Precise Terahertz Applications

“…In particular, studies on terahertz (THz) nonlinear phenomena in various materials, often require intense ultrashort THz pulses with microjoule-level energy and electric field strength of >100 kV/cm, are currently regarded as an unexplored new research area [4][5][6][7]. Since the availability of compact high-power ultrashort THz sources is quite limited yet, development of such sources is an essential step for advanced nonlinear spectroscopy and applications in the THz frequency range.…”

Nonlinear free-carrier velocity induced by intense terahertz pulse in photoexcited semiconductor materials

“…As a result, the electron mobility is decreased because the electron at L and X valley has larger effective mass than at Γ valley. Recently, the intense few-cycle THz electric field pulse was utilized to reveal the ultrafast intervalley-electron-scattering dynamics in n-doped InGaAs and photoexcited GaAs [15,16] , which dominate the observed significant THz absorption bleaching. On the other hand, the electron velocity overshoot can take place over the sub-picosecond time scale under a strong step DC electric field due to the intervalley electron scattering in the semiconductor with multivalley conduction band structure.…”