Collision-induced six-wave-mixing and subharmonic resonances: experiments in a sodium-seeded flame

Jonas Bengtsson

Rick P. Trebino, Larry A. Rahn

Using four-, six-, and eight-wave-mixing geometries, we observe subharmonic resonances in collision-enhanced spectra in a sodium-seeded hydrogen-air flame. Appearing at high intensity, these resonances occur at +/-1/2, +/-1/3, +/-1/4, and +/-1/5 times the frequency of the ground-state hyperfine splitting omega(hfs). We argue that these resonances result from higher-order processes, specifically chi((n)), where n >/= 5. In particular, to describe the resonances at +/-omega(hfs)/5, at least chi((13)) is required. These high-order collision-enhanced effects are true perturbative nonlinearities and not sequential four-wave mixing processes.

Rick P. Trebino, Larry A. Rahn

We observe collision‐induced four‐wave‐mixing resonances—Zeeman and hyperfine coherences and ground‐state‐spin gratings—in a sodium‐seeded hydrogen‐air flame. We see several new characteristics of collision‐induced phenomena at high intensity.

Suneel Pratap Singh, Charles M. Bowden

Nadav Horesh, Yehiam Prior

John T. Fourkas, Timothy R. Brewer, Hack-Jin Kim +1 more

Picosecond four-wave mixing experiments have been used to study collisions in a Na-seeded, premixed, methane-air flame. Population gratings are used to measure Na excited-state quenching collision rates, while polarization gratings are used to measure Na ground-state hyperfine coherence randomizing collision rates and overall Na diffusion rates, even though these processes are slower than the excited-state quenching rate.