Abstract

Pulse-width measurements in a single-shot geometry are convenient for high-energy pulses and low-repetition-rate lasers. However, if the signal beam does not propagate along the bisector of the incoming beams, inherent problems due to the finite thickness of the nonlinear medium degrade the temporal resolution. For example, for a single-shot PG-FROG, the signal propagates in the direction of one of the beams. Figure 1 shows the wave fronts of both beams at a time t and at a later time t + T. The angle between the two beams is 2Θ, the angle between the normal of the Kerr medium of thickness, is l and the propagation direction of the signal is ϕ. The smearing problem due to the finite thickness of the nonlinear medium can be clearly seen in the case of 10-fs pulses. Geometry, not dispersion, is the limiting factor for the case considered here; dispersion due to the Kerr medium would broaden the pulse by less than 10%. However, Fig. 1 shows that the temporal width of the measured signal broadens from 10 fs to 20 fs because of to the geometry (Θ = 4, ϕ = 0, I = 400 μm, and the index of refraction is 1.5)—an increase of 100%.

© 1995 Optical Society of America