One should think that the optical phase evolution of a common pulsed focused laser beam is known for a long time already — that’s not the case! Our lab in collaboration with colleagues around Prof. Gerhard Paulus’s group in Jena has, for the first time, measured the phase in the focal area of such a laser beam. We have used carrier-envelope-phase-sensitive photo-emission from a nanometer-sharp neede tip, which we raster-scanned through the focus. Interestingly, the focal phase evolution can be very different, depending on the exact input beam parameters, in particular the spectral distribution of the Rayleigh range. After these measurements, we are quite convinced that many labs employing ultrashort pulse lasers assume a focal phase evolution that does not correspond to reality.
Our contribution has just appeared in Nature Physics.
The FAU issued a press release that can be found here.