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. To demonstrate this, we extend 2-BA concept in a technique that we call 2-beam constant-amplitude photocurrent spectroscopy (2-BCAmP) to study absorption of a tightly focused, mode-locked or continuous-wave, 800 nm laser by a GaAsP photodiode. 2-BCAmP allows us to measure the effective order of the absorption process at any desired value of the photocurrent or photovoltage, as opposed to traditional approaches that require the measurement of the observable over several orders of magnitude of input intensity. We further demonstrate how to extract the relative contributions of two different absorption orders from non-integral 2-BCAmP exponents, as well as how to use these data to validate the model of the absorption orders that are involved in photocurrent generation.