Analysis of phase instabilities in amplitude swing for ultrashort pulse train characterization

Abstract

The temporal dynamics of ultrashort pulses are a fundamental feature in ultrafast optics. These dynamics can often be extracted from a two-dimensional trace consisting of a set of nonlinear spectra, using an iterative algorithm. Typically, the measurement of this trace requires integrating the signal of many pulses, which implies that the trace does not correspond to a single pulse when shot-to-shot variations occur. In this case, the pulse train can be characterized statistically, by a base pulse and a metric that quantifies the instabilities. Here, we demonstrate that the amplitude swing technique is sensitive to instabilities, which manifest as two distinct imprints on the measurement. First, we analyze the terms that compose the amplitude swing signal. Then, we study two parameters to quantify the instabilities, related to a shift in the minima of the trace marginal, and to the filling of the trace minima zones, respectively. Finally, we apply these strategies to characterize simulated unstable pulse trains, using a simple technique.