Analysis of space-time coupling in SEA-SPIDER measurements

Pulse characterisation methods based on non-collinear frequency mixing (NCFM) can introduce additional space-time coupling (STC) in the measurement. Thus it is necessary to re-examine the NCFM process in order to be able to measure STC accurately with these devices. SEA-SPIDER is one characterisation method that in principle can measure the temporal electric field of a pulse as a function of a single spatial dimension, thus measuring STC (but not the spatial phase). This method has been modelled specifically and found it is necessary to account for this additional ´geometric´ STC for few-cycle pulses. SEA-SPIDER has already been demonstrated as an excellent candidate for measuring extremely large bandwidth pulses. In addition, it has been shown that it is possible to measure the STC of a pulse in one spatial dimension. However, the non-collinear sum-frequency generation used in the device introduces a small amount of additional STC coupling which can easily be corrected for. This analysis will prove invaluable as it allows one to obtain more complete and accurate information about their pulses. The ideas and analysis presented here can also be applied to other characterisation methods that claim to be able to measure STC.