Improving signal-to-noise ratios in pump-probe spectroscopy on light-sensitive samples by adapting pulse repetition rates

Abstract

Ultrafast optical pump-probe spectroscopy is a powerful tool to study dynamics in solid materials on femto- and picosecond timescales. In such experiments, a pump pulse induces dynamics inside a sample by impulsive light-matter interaction, which can be detected using a time-delayed probe pulse. In addition to the desired dynamics, the initial interaction may also lead to unwanted effects that can result in irreversible changes and even damage. Therefore, the achievable signal strength is often limited by the pumping conditions that a sample can sustain. Here we investigate the optimization of ultrafast photoacoustics in various solid thin films. We perform systematic experiments aimed at maximizing the achievable signal-to-noise ratio (SNR) in a given measurement time while limiting sample damage. By varying pump and probe pulse energies, average pump fluence, and repetition rate, we identify different paths towards optimal SNR depending on material properties. Our results provide a strategy for the design of pump-probe experiments, to optimize achievable SNR for samples in which different damage mechanisms may dominate.