Spatial measurement of ultrashort light pulses using two photon absorption in a colliding geometry

In this work the spatial measurement of ultrashort light pulses through two photon absorption (TPA) is analyzed. The method is based on a Michelson interferometer configuration in a colliding geometry where the light pulses meet each other in a cell with Rhodamine B in ethanol, which emits a fluorescence that can be detected with a standard digital camera. The analysis of the experimental spatial trace as well as the theoretical derivation show that the Full Width at Half Maximum (FWHM) measured is FWHMmeasured=FWHMsingle_pulse/2 instead of the general value 2 FWHM single_pulse of temporal or spatial collinear approaches. The influence of the pulse chirp on the measurement and the error caused by the camera misalignment are analyzed.