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Transient absorption spectroscopy (TAS) is a field of study that investigates the dynamic process of chemical compounds. Thanks to the recent emergence of ultrafast pulsed lasers, TAS now extends its reach to studying photochemical reactions occurring within few femtosecond to nanosecond timescales. With ultrafast TAS, changes in sample absorbance or transmittance over time following excitation by pulsed light can be measured at a high temporal resolution -tens of femtoseconds. An application of ultrafast TAS is lifetime measurement for fluorescence decay. However, due to various noise sources (sensor noise, shot noise, unintended photochemical reactions, etc.) during measurement, obtaining a reliable lifetime value often necessitates extensive repetition resulting in experiments lasting several hours. In this paper, we introduce an effective time sampling strategy tailored for lifetime measurement from noisy transient signals. We start with a well-established non-linear curve fitting algorithm and demonstrate that sampling time shifts that maximize the signal derivative (t=τ) will minimize the variance in lifetime estimation. Additionally, we reduce the number of parameters by normalization to ensures the correctness of our algorithm. We demonstrate using simulation that our proposed method outperforms conventional time sampling or normalization methods across various conditions. Especially, we found that proposed method gives same error with 5.5 x less samples compared to the common TAS measurement strategy that uses exponential time sampling with full parameter curve-fitting. Moreover, through real-world TAS measurements, we show that our technique results in 2 - 8 x less standard deviation compared to baseline methods. We expect that our algorithm will be valuable not only for researchers who use TAS but also for researchers across various fields who use time-gated transient cameras for lifetime analysis. 

A catalyst enhances a reaction pathway without itself being consumed or changed. Recently, there has been growing interest in the concept of “photon catalysis” in which nonresonant photons, which are neither absorbed nor scattered, promote reactions. The driving force behind this effect is the interaction between the strong electric field associated with a pulsed, focused laser and the polarizability of the reacting system. In this study, the effect of near-infrared, nonresonant radiation on the photodissociation of deuterium iodide is demonstrated. We use nanosecond pulses rather than time-resolved spectroscopy to investigate the average effect of the electric field on the branching ratio for forming D + I( 2 P 3/2 ) and D + I( 2 P 1/2 ). Changes in the measured D-atom speeds between field-free and strong-field conditions confirm substantial differences in dissociation dynamics. Both the magnitude and direction of change in the branching ratios are dependent upon the photodissociation wavelength. Experiments and theoretical calculations confirm that the mechanism for photon catalysis under these conditions is dynamic Stark shifting of potential energy surfaces rather than electric-field-induced alignment of reagent molecules.