Spatiotemporal structure of isodiffracting ultrashort electromagnetic pulses

We present a model of isodiffracting single-cycle and few-cycle ultrashort electromagnetic pulses. The model is based on exact solutions of the time-d ependent paraxial wave equation with space-time coupling effects included. The spatiotemporal structure of these pulses is characterized by a scaling parameter which relates off-axis pulse shapes to the axial temporal wavefor ms. Depending on the spectrum a pulse may transform itself from a single-cy cle pulse to a multicycle pulse along the radial coordinate. This model is also used to describe recirculating pulses in a curved mirror cavity resona tor. The Gouy phase Shift contributes an absolute phase that results in a p ulse-to-pulse temporal instability. PACS number(s): 42.25.Bs, 42.65.Re, 41. 20.Jb, 42.60.Da.