 Todd S. Rose

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.^[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.^[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 $2\Delta x$, givingA $150\mu \mathrm{m}$ 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 $\sqrt{{\tau }_1^2+{\tau }_2^2}\approx 128\mathrm{fs}$. 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.