High Sensitivity Nanosecond Mid-Infrared Transient Absorption Spectrometer Enabling Low Excitation Density Measurements of Electronic Materials

A dispersive nanosecond transient absorption instrument was developed to enable rapid time-resolved and steady-state measurements in the mid-infrared (mid-IR) region for thin films without the need for gated integrators or lock-in amplifiers. Two detectors are used depending on the experimental needs (100 MHz and 16 MHz) with time resolution from nano-millisecond and spectral coverage from 1000-5000 cm^-1 (2000-10 000 nm). The instrument utilizes flexible digitization resolution (8 bit to 14 bit) to enable high sensitivity (10^-5) measurements on thin films under low excitation (<50 μJ/cm²). We highlight the instrument's improvement over prior state-of-the-art time-resolved capabilities by measuring transient species (e.g., polarons) under extremely low energy densities (<5 μJ/cm²) in less than 10 minutes to achieve high fidelity signals. Additionally, to highlight the spectral capabilities we study two optoelectronic materials for which we resolve vibrational features as small as 10 μOD.