Time-Frequency Spectroscopy of GaAs Transient Dispersion Using Few-Cycle Pump-Probe Reflectometry

Abstract

The rapid development of new photonic materials calls for simple yet effective approaches to characterize ultrafast dynamics in materials and devices. Here we demonstrate time-frequency transient reflectometry based on a compact, few-cycle pump-probe reflectometer. The system simultaneously features a broad spectral range (300 nm) and fine temporal resolution (10 fs), and it requires only a femtosecond oscillator. With this capability, we report a time-frequency spectroscopic measurement of the transient dispersion of $\mathrm{Ga}\mathrm{As}$ near its band gap. Our results map important carrier dynamics such as carrier cooling, carrier decay, band filling, and band-gap renormalization on a single two-dimensional graph, offering a comprehensive picture of these processes and revealing details unattainable with conventional methods.