Pulse-length-limited ultrafast pump-probe spectroscopy in a single laser shot

We demonstrate a scheme for taking single-shot pump-probe data with femtosecond time resolution. Data recorded from a 100-microm-thick dye solution show that pulse-length-limited resolution can be achieved readily with 70-fs laser pulses. This technique opens the door for the study of irreversible ultrafast processes in a wide variety of solids. Also, unlike with conventional techniques, in this method multiple-shot data are not affected by shot-to-shot laser intensity fluctuations.

Extra resonances in time-domain four-wave mixing

We show that extra resonances, such as those caused in frequency-domain nonlinear wave mixing by pure dephasing or laser fluctuations, can also be induced by operation in the time domain. These pulse-length-induced extra resonances arise in transient-grating experiments when the laser pulses are short enough that a steady state cannot be achieved during the excitation process. We show theoretically that these resonances increase in strength with decreasing excitation pulse length until the pulse length becomes shorter than the dephasing time of the medium and quote an experimental example to support this interpretation.

Picosecond time-resolved four-wave mixing experiments in sodium-seeded flames

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.