Oxygen rotational Raman linewidth determination considering nonmonoexponential decoherence behavior

Abstract

The rotational Raman linewidth is a vital empirical parameter in determining temperature and concentration in combustion environments from pure rotational anti‐Stokes Raman spectroscopy (RCARS). The Raman linewidth is regularly determined from the coherence dephasing time constant on a picosecond time scale. Oxy‐fuel combustion processes cannot be studied applying the well‐described nitrogen evaluation but are typically based on oxygen evaluation. Therefore, the dephasing behavior of the rotational Raman coherences of oxygen was studied by picosecond time resolved RCARS. In opposite to nitrogen, the dephasing in oxygen shows distinct quantum beating rendering monoexponential fitting functions unsuited for the evaluation. Therefore, collisional dephasing time constants were obtained from a coherent beating model function. The acquired Raman linewidths show comparable trends with increasing temperature and rotational quantum number as nitrogen but differ from O2‐linewidths used for evaluations up to now. Therefore, an improvement of temperature and concentration evaluations based on oxygen RCARS measurements by application of the S‐branch linewidth can be expected.

Recent advances in linear and nonlinear Raman spectroscopy. Part XIV

“…Based on their work, they were able to achieve good control over the measurement of vibrational bands by CARS microscopy by means of optimized performances in specific spectral bands. Hoelzer et al [ 103 ] used nonmonoexponential decoherence behavior to determine oxygen rotational Raman linewidths. Collisional dephasing time constants were obtained from a coherent beating model function.…”

Development and applications of nonlinear optical spectroscopy: 17th ECONOS/37th ECW meeting in Milan (Italy)

“…Therefore, it is not surprising that four papers are related to this area. Hölzer et al determined rotational Raman linewidths of molecular oxygen using picosecond time‐resolved rotational CARS. They found that in contrast to the commonly used nitrogen, the rotational dephasing in oxygen shows distinct quantum beating rendering mono‐exponential fitting functions.…”