Optimization of pump–probe signal requires a complete
understanding
of how signal scales with experimental factors. In simple systems,
signal scales quadratically with molar absorptivity, and linearly
with fluence, concentration, and path length. In practice, scaling
factors weaken beyond certain thresholds (e.g., OD > 0.1) due to
asymptotic
limits related to optical density, fluence and path length. While
computational models can accurately account for subdued scaling, quantitative
explanations often appear quite technical in the literature. This
Perspective aims to present a simpler understanding of the subject
with concise formulas for estimating absolute magnitudes of signal
under both ordinary and asymptotic scaling conditions. This formulation
may be more appealing for spectroscopists seeking rough estimates
of signal or relative comparisons. We identify scaling dependencies
of signal with respect to experimental parameters and discuss applications
for improving signal under broad conditions. We also review other
signal enhancement methods, such as local-oscillator attenuation and
plasmonic enhancement, and discuss respective benefits and challenges
regarding asymptotic limits that signal cannot exceed.