ABSTRACT
This chapter considers measuring similar dynamics using coherently scattered light via nonlinear optical spectroscopy. While these techniques typically measure the fluence of the probe beam, there are many variations that involve slightly different resonance conditions and beam. Coherent optical spectroscopies typically offer relatively large signals, as they involve a coherent buildup of the signal over the sample. This means that photon or electron/ion counting are generally not required. In addition, these techniques are well suited to condensed-phase samples since they do not require vacuum. Fluctuations in the pump pulse energy drive reflectivity changes of the probe unrelated to phonon dynamics that can overwhelm the small changes in reflectivity resulting from phonon oscillation. However, any changes in reflectivity unrelated to phonon motion are independent of the probe polarization, and so the balanced detection arrangement subtracts these off.
