OPTIMIZATION OF SIGNAL-TO-NOISE RATIOS IN PUMP-PROBE SPECTROSCOPY

Analytic expressions for the signal-to-noise ratio in time resolved pu mp-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 scan ning'') is compared to the case of repetitively averaging many scans t ogether (''fast scanning'') without pump modulation. Data are presente d from a pump-probe experiment on an amorphous semiconductor thin film which agrees with the simple model developed in this article. The mod el can be used to predict the optimal scan frequency if the laser nois e power spectrum, the magnitude of the signal, and the noise subtracti on efficiency are known.