2-beam action spectroscopy for probing multiphoton absorption processes in semiconductors*

We recently introduced a new class of methods, called two-beam action (2-BA) spectroscopies for determining the order of effective absorptive nonlinearity in different materials. The 2-BA spectroscopy approach offers significant advantages over traditional logarithmic plots of an observable as a function of average excitation power, particularly when multiple orders of absorption are involved. In this work, we extend the 2-BA concept in a technique that we call 2-beam constant-amplitude photocurrent spectroscopy (2-BCAmP). We use this technique to study multiphoton absorption in wide-bandgap semiconductors. 2-BCAmP allows us for the measurement of the effective order of the absorption process at any desired value of the photocurrent or photovoltage, as opposed to traditional approaches that require data that span several orders of magnitude of average excitation power. Furthermore, the relative contributions of two different absorption orders can be extracted from non-integral 2-BCAmP exponents, and these data to validate the model of the absorption orders that are involved in photocurrent generation.