Optimization of signal‐to‐noise ratios in pump‐probe spectroscopy

Analytic expressions for the signal‐to‐noise ratio in time resolved pump‐probe spectroscopy experiments are presented for two common signal averaging schemes in the presence of strongly correlated laser noise. The case of modulated pump/synchronous probe demodulation (‘‘slow scanning’’) is compared to the case of repetitively averaging many scans together (‘‘fast scanning’’) without pump modulation. Data are presented from a pump‐probe experiment on an amorphous semiconductor thin film which agrees with the simple model developed in this article. The model can be used to predict the optimal scan frequency if the laser noise power spectrum, the magnitude of the signal, and the noise subtraction efficiency are known.