Development of a simplified dual-pump dual-broadband coherent anti-Stokes Raman scattering system.

A dual-pump dual-broadband coherent anti-Stokes Raman scattering (CARS) setup for simultaneous pure rotational and vibrational CARS is further developed by reducing the experimental efforts due to the use of only one detection system. With this system dual-pump CARS for probing ro-vibrational transitions of N(2)/CO/H(2) and dual-broadband CARS for pure rotational transitions of N(2)/O(2)/CO/CO(2) are applicable simultaneously. In this work the improvements to the setup and the data evaluation are described.

Determination of probe volume dimensions in coherent measurement techniques.

When investigating combustion phenomena with pump-probe techniques, the spatial resolution is given by the overlapping region of the laser beams and thus defines the probe volume size. The size of this probe volume becomes important when the length scales of interest are on the same order or smaller. We present a new approach to measure the probe volume in three dimensions, which can be used to determine the probe volume length, diameter, and shape.

Two-photon stimulated Raman excitation of thermal laser-induced gratings in molecular gases using broadband radiation of a single laser.

For the first time to our knowledge, thermal laser-induced gratings (LIGs), generated via two-photon stimulated Raman excitation of pure rotational (and low-lying vibrational) transitions in molecules employing broadband radiation of a single pump laser, are observed. The efficiency of LIGs excitation using a few ns pulse duration dye laser with the spectral width of about 400 cm(-1), which covers the frequency range of the characteristic rotational transitions, is experimentally investigated in a number of molecular gases (N(2), CO(2), C(3)H(8)) at room temperature and pressures of 0.1-5 bar.

Time-resolved measurement of the local equivalence ratio in a gaseous propane injection process using laser-induced gratings.

For the first time laser-induced gratings (LIGs) have been used for the investigation of a non-stationary pulse-repetitive injection process of gaseous propane, C(3)H(8), into air. By recording and evaluating single-shot LIG signals it was possible to determine, on a cycle-averaged basis, the temporal evolution of the local (within a probe volume 300 microm in diameter and 10 mm in length) equivalence ratio and by this the fuel-air ratio. Two different data treatment strategies, subject to C(3)H(8) concentration range, were first tested at stationary conditions and then used to evaluate the LIG signals obtained during the injection process.

Combined coherent anti-Stokes Raman spectroscopy and linear Raman spectroscopy for simultaneous temperature and multiple species measurements.

The simultaneous application of pure rotational coherent anti-Stokes Raman spectroscopy (CARS) and vibrational linear Raman spectroscopy (LRS) for the measurement of temperature and species concentrations in combustion systems is demonstrated. In addition to the standard rotational CARS experimental setup, only one detection system (spectrometer and intensified CCD camera) for the collection of the LRS signals was applied. The emission of the broadband dye laser used for CARS was shifted to the deep red to avoid interferences with the LRS signals located in the visible region.

Simultaneous temperature and exhaust-gas recirculation-measurements in a homogeneous charge-compression ignition engine by use of pure rotational coherent anti-Stokes Raman spectroscopy.

Pure rotational coherent anti-Stokes Raman spectroscopy was used for the simultaneous determination of temperature and exhaust-gas recirculation in a homogeneous charge-compression ignition engine. Measurements were performed in a production-line four-cylinder gasoline engine operated with standard gasoline fuel through small optical line-of-sight accesses. The homogenization process of fresh intake air with recirculated exhaust gas was observed during the compression stroke, and the effect of charge temperature on combustion timing is shown.

Application of an optical pulse stretcher to coherent anti-Stokes Raman spectroscopy.

An external optical cavity pulse stretcher for nanosecond-long laser pulses has been applied to coherent anti-Stokes Raman spectroscopy (CARS). An increased signal-to-noise ratio was achieved for both vibrational and pure rotational CARS, while the power density of the laser beams remained constant. Moreover, it was demonstrated that the use of the pulse stretcher also leads to improved precision of the determined temperatures and concentrations as a result of repeated excitation of the dye laser.