In this Research Letter, we study the transient carrier dynamics and the nonlinear terahertz effects induced by an intense multicycle terahertz pulse in the $n$-doped semiconductor ${\mathrm{In}}_{0.57}{\mathrm{Ga}}_{0.43}\mathrm{As}$. For incident terahertz pulses with relatively high frequency $\ge 1$ THz, we reveal the generation of low- and high-frequency components in the transmitted intensity spectra. We study the time emission of these components at different frequencies using the Gábor transform, showing that the low- and high-frequency components are due to the nonparabolicity of the conduction band. Our results demonstrate that for a multicycle terahertz pulse, we generate a distorted biphasic truncated exponential current with the driving terahertz fields, leading to discrete high-order harmonic generation in the transmitted intensity spectra.

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• Carrier dynamics
• Carrier generation & recombination
• Nonlinear optics
• Doped semiconductors
• Boltzmann theory
• Monte Carlo methods