= A. Hall
{disambiguate=optical physicist}
{c}
\b[A. Hall] is a coauthor of the1999 Central Laser Facility report describing a single-shot optical correlation instrument with a <charge-coupled device> readout.<A Single Shot 3rd Order Cross-Correlator for Pulse Contrast and Pulse Shape Measurements by J. Collier and others>[Printedpp194–195, byline and Figure2]{ref}
A detector coordinate becomes a delay measurement only through <measurement calibration>. For an original example, suppose a known change of optical delay by200femtoseconds shifts a feature by0.80millimeters on the detector image. The calibrated scale is
$$
k=\frac{200\,\mathrm{fs}}{0.80\,\mathrm{mm}}
=250\,\mathrm{fs/mm}.
$$
With10micrometer pixel spacing, adjacent pixels represent2.5femtoseconds on that scale. A feature spanning20pixels spans50femtoseconds in the sampled delay coordinate.
This conversion does not prove that the optical apparatus resolves2.5femtoseconds. Pixel sampling, the optical response and uncertainty in the delay mapping are separate properties. A densely sampled broad response remains broad. Nor does a feature's correlation width necessarily equal the underlying pulse width, as the <Gaussian pulse> example in <T. J. Spencer (optical physicist)> demonstrates.
The example shows why a spatially recorded <third-order intensity autocorrelation> requires both a calibrated coordinate conversion and an independently understood response. The numerical values above are stipulated for illustration, rather than specifications assigned to the historical instrument.
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