Interferometric quantum control (IQC) by fs/ns rotational coherent anti-Stokes Raman spectroscopy (RCARS).

A new rotational coherent anti-Stokes Raman spectroscopy (RCARS) concept based on interferometric quantum control (IQC) is demonstrated. Two wavepackets originating from pure rotational states are created by a femtosecond stimulated rotational Raman interaction. The two Raman responses are instantly probed by a single-mode ns pulse generating two interfering RCARS polarizations. The resulting signal is an IQC-RCARS spectrum detected by a streak camera. Here we demonstrate IQC-interferograms of N2 by varying the temporal separation between the two fs pulses within a full rotational revival period, as well as signal amplification and selective detection of nuclear-spin isomers at room conditions and inside a flame.

Simultaneous single-shot imaging of H and O atoms in premixed turbulent flames using femtosecond two-photon laser-induced fluorescence.

A method based on femtosecond two-photon excitation has been developed for simultaneous visualization of interference-free fluorescence of H and O atoms in turbulent flames. This work shows pioneering results on single-shot simultaneous imaging of these radicals under non-stationary flame conditions. The fluorescence signal, showing the distribution of H and O radicals in premixed CH4/O2 flames was investigated for equivalence ratios ranging from ϕ = 0.8 to ϕ = 1.3. The images have been quantified through calibration measurements and indicate single-shot detection limits on the order of a few percent. Experimental profiles have also been compared with profiles from flame simulations, showing similar trends.

Single-shot coherent control of molecular rotation by fs/ns rotational coherent anti-Stokes Raman spectroscopy.

We present a novel method, to our knowledge, to control the shape of the spectra using 2-beam hybrid femtosecond (fs)/nanosecond (ns) coherent anti-Stokes Raman scattering (RCARS). The method is demonstrated experimentally and theoretically by utilizing a species-selective excitation approach via a field-free molecular alignment as an illustrative example. Two non-resonant fs laser pulses with proper delay selectively create and then annihilate N2 resonances in a binary mixture with O2 molecules. The RCARS signal is simultaneously resolved in spectral and temporal domains within a single-shot acquisition. The method requires very low pulse energies for excitation, hence minimizing multiphoton ionization probability, allowing for coherent control at various temperatures and pressures, with spectroscopic applications in non-stationary and unpredictable reacting flows.