Optimizing Detection Schemes for Broadband Pump-Probe Microscopy

Although similar to more commonly implemented single wavelength approaches, broadband pump-probe or transient absorption microscopy presents unique experimental challenges due to the simultaneous requirements of a broadband probe pulse and a small sample volume. Here we provide an in-depth analysis of broadband detection schemes and their common noise sources to provide strategies for balancing the conflicting needs of high sensitivity and low probe fluence. We show that broadband pump-probe microscopy is atypically sensitive to laser shot noise and therefore, low pump on/off modulation frequencies, on the order of 100 s of Hz to a few kHz, are essential to measure small ( $~{10}^{-3}-{10}^{-4}$ ) amplitude transient spectra while remaining in the perturbative limit.