= Todd S. Rose
{c}
\b[Todd S. Rose] was the first-listed author, with <Mark J. Rosker> and <Ahmed H. Zewail>, of the 1988 report of femtosecond <wave packet> oscillations in dissociation reactions. The primary Caltech record preserves the full published first name and middle initial.<Femtosecond real-time observation of wave packet oscillations (resonance) in dissociation reactions by Todd S. Rose and others>[author repository, ordered creator list]{ref}
The associated <pump-probe spectroscopy> prepares a molecular ensemble with one pulse and samples its subsequent evolution with a delayed pulse. Repeating the experiment at different delays builds a trace of the chosen spectroscopic response. Zewail's lecture relates the NaI traces to repeated motion and the appearance of fragments.<Femtochemistry: Atomic-Scale Dynamics of the Chemical Bond Using Ultrafast Lasers by Ahmed H. Zewail>[pump–probe method; The NaI Discovery and Figure 15]{ref}
An original timing calculation shows how a mechanical displacement accesses a molecular timescale. If a delay stage moves a retroreflecting mirror by $\Delta x$, its round-trip optical path changes by $2\Delta x$, giving
$$
\Delta t=\frac{2\Delta x}c.
$$
A $150\,\mu\mathrm m$ displacement therefore changes the delay by approximately $1.00\,\mathrm{ps}$. The factor of two belongs to this specified return-path geometry; a single-pass path change would give another relation.
Delay increments are also distinct from temporal resolution. For an illustrative ideal cross-correlation of Gaussian intensity pulses with <full widths at half maximum> $\tau_1=100\,\mathrm{fs}$ and $\tau_2=80\,\mathrm{fs}$, the width is $\sqrt{\tau_1^2+\tau_2^2}\approx128\,\mathrm{fs}$. Sampling that response every $10\,\mathrm{fs}$ does not make the pulses ten femtoseconds wide. These hypothetical dimensions and widths explain apparatus interpretation rather than supplying unverified parameters for Rose's experiment.
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