Semiconductor saturable absorbers for ultrafast THz signals

TL;DR

This paper demonstrates the use of n-type semiconductors GaAs, GaP, and Ge as saturable absorbers for ultrafast THz signals at room temperature, revealing their nonlinear response and pulse-shaping capabilities.

Contribution

It introduces a novel application of semiconductor saturable absorbers in the THz range, with detailed characterization and analysis of their nonlinear behavior at room temperature.

Findings

Semiconductors exhibit saturable absorption behavior in THz frequencies.

High-field THz pulses cause pulse shortening and increase in group refractive index.

Saturable absorber parameters are quantitatively extracted from experimental data.

Abstract

We demonstrate saturable absorber behavior of n-type semiconductors GaAs, GaP and Ge in THz frequency range at room temperature using nonlinear THz spectroscopy. The saturation mechanism is based on a decrease in electron conductivity of semiconductors at high electron momentum states, due to conduction band nonparabolicity and scattering into satellite valleys in strong THz fields. Saturable absorber parameters, such as linear and non-saturable transmission, and saturation fluence, are extracted by fits to a classic saturable absorber model. Further, we observe THz pulse shortening, and an increase of the group refractive index of the samples at higher THz pulse peak fields.