Extreme pulse-front tilt from an etalon

Angular dispersion—whether from prisms, diffraction gratings, or etalons—is well known to result in a pulse-front tilt. Focusing into a tilted etalon, in particular, generates a huge angular dispersion, which is very useful for high-resolution spectrometers and pulse shapers. Here we demonstrate experimentally that, due to the large angular dispersion $\left(\sim 3°/\text{nm}\right)$, the pulse directly out of an etalon can have a huge pulse-front tilt—89.9°—which can cause one side of a few-millimeter-wide beam to lead the other by 1 m, that is, several nanoseconds. We propagated a 700 ps near-transform-limited pulse through the etalon and measured the resulting spatiotemporal field, confirming this result. To make this measurement, we used a high-spectral-resolution version of crossed-beam spectral interferometry, which used a high-resolution etalon spectrometer. We also performed simulations, which we found to be in good agreement with our measurements.