We show that a frequency-resolved optical gating device using (1) a thick nonlinear crystal to replace the usual thin crystal and spectrometer and (2) a Fresnel biprism to replace the beam splitter and delay line yields a remarkably simple single-shot ultrashort-pulse intensity-and-phase measurement device with no sensitive alignment parameters and significantly greater sensitivity.

Cross-correlation frequency-resolved optical gating with an angle-dithered nonlinear-optical crystal permits measurement of the intensity and the phase of the ultrabroadband (as much as 1200 nm wide) continuum generated from microstructure optical fiber. Retrieval revealed fine-scale structure in the continuum spectrum. Simulations and single-shot spectrum measurements confirmed that the fine structure does exist on a single-shot basis but washes out when many shots are averaged.

Numerical simulations are used to study the temporal and spectral characteristics of broadband supercontinua generated in photonic crystal fiber. In particular, the simulations are used to follow the evolution with propagation distance of the temporal intensity, the spectrum, and the cross-correlation frequency resolved optical gating (XFROG) trace. The simulations allow several important physical processes responsible for supercontinuum generation to be identified and, moreover, illustrate how the XFROG trace provides an intuitive means of interpreting correlated temporal and spectral features of the supercontinuum. Good qualitative agreement with preliminary XFROG measurements is observed.

We show that the spatio-temporal distortion, pulse-front tilt, is naturally, easily, and sensitively measured by the recently demonstrated, extremely simple variation of single-shot second-harmonic generation frequency-resolved optical gating (SHG FROG): GRENOUILLE. While GRENOUILLE traces are ordinarily centered on the zero of delay, a pulse with pulse-front tilt yields a trace whose center is shifted to a nonzero delay that is proportional to the pulse-front tilt. As a result, the trace-center shift reveals both the magnitude and sign of the pulse-front tilt-independent of the temporal pulse intensity and phase. The effects of pulse-front tilt can then easily be removed from the trace and the intensity and phase vs. time also retrieved, yielding a full description of the pulse in space and time.

We show that the spatio-temporal distortion, spatial chirp, is naturally and easily measured by single-shot versions of second-harmonic generation frequency-resolved optical gating (SHG FROG) (including the extremely simple version, GRENOUILLE);. While SHG FROG traces are ordinarily symmetrical, a pulse with spatial chirp yields a trace with a shear that is approximately twice the pulse spatial chirp. As a result, the trace shear unambiguously reveals both the magnitude and sign of the pulse spatial chirp. The effects of spatial chirp can then be removed from the trace and the intensity and phase vs. time also retrieved, yielding a full description of the spatially chirped pulse in space and time.

Ultrashort-pulse characterization techniques, such as the numerous variants of frequency-resolved optical gating (FROG) and spectral phase interferometry for direct electric-field reconstruction, fail to fully determine the relative phases of well-separated frequency components. If well-separated frequency components are also well separated in time, the cross-correlation variants (e.g., XFROG) succeed, but only if short, wellcharacterized gate pulses are used.

We show that the usual phase-matching-bandwidth constraint in ultrashort-laser-pulse measurement techniques is overly restrictive. Specifically, the phase-matching bandwidth need not exceed the pulse bandwidth on every pulse. Instead, only the phase-matching bandwidth integrated over the measurement period need exceed the pulse bandwidth. We show that angle-dithering a second-harmonic-generation crystal that is otherwise too narrowband (that is, too thick) can yield sufficient phase-matching bandwidth and an accurate pulse measurement. We apply this technique to frequency-resolved optical gating (FROG) and show that accurate pulse measurements can be made using a comparatively very thick and hence narrowband crystal. An additional advantage of using a thick crystal is increased signal strength.

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