Wave optical modelling of focusing of an ultra short pulse

The spatial-temporal evolution of an ultrashort pulse at different planes on propagation through a spherical lens is modelled using an efficient numerical algorithm. With this model it is possible to observe the on- and off-axis pulse evolution at any arbitrary plane. This model is applicable to pulses of arbitrary spatial and temporal shapes and can be used beyond paraxial approximation. We can obtain the exact amplitude information at any plane fairly easily. The asymmetry of the pulse shape at the focus is reported for the first time. The focusing of a pulse with TEM01 spatial profile has been considered as an example and its evolution is analysed at different planes of propagation.