  Temporal pulse characterization methods can often not be applied to UV pulses
due to the lack of suitable nonlinear crystals and very low pulse energies.
Here, a method is introduced for the characterization of two unknown and
independent laser pulses. The applicability is broad, but the method is
especially useful for pulses in the deep UV, because pulse energies on the
picojoule-scale suffice. The basis is a spectral analysis of the two
interfering UV pulses, while one of the pulses is phase shifted by an unknown
VIS-IR pulse via cross-phase modulation. The pulse retrieval is analytic and
the fidelity can be checked by comparing the complex-valued data trace with the
retrieved trace.
