Single-shot transient absorption spectroscopy techniques and design principles

Abstract

Single-shot transient absorption (SSTA) spectroscopy is fundamentally identical to transient absorption (TA) spectroscopy but differs in its implementation to enable the measurement of sample response at a range of pump–probe time delays in a single laser shot. As in TA, a pump pulse in SSTA photoexcites a sample, inducing a change in the absorption of a probe pulse. Both commercial and home-built TA instruments typically execute serial measurements at a range of pump–probe time delays to yield transients that report on the dynamics of the photoexcited species, with the sample returning to the same relaxed state between each measurement. SSTA instruments acquire a range of pump–probe time delays simultaneously by somehow encoding the time delay into the profile of the probe beam. This dramatically reduces the time required for SSTA measurements, enabling the measurement of unstable systems undergoing irreversible processes that cannot be accurately characterized using typical TA instruments. The implementation of the encoded time delay must be appropriately designed and carefully calibrated to suit the targeted system and ensure accurate measurements. This review describes techniques used to encode the time delay and design principles for SSTA instruments. Strategies are presented to implement a broadband probe, account for spatial variations in pump and probe beam profiles that influence the intensity and noise of the spatially encoded signal, optimize detection, and correct for dynamic background signals. With these design principles in place, SSTA is capable of measuring an array of unstable and evolving systems that cannot be addressed using typical TA instruments.