Stray light rejection in rotational coherent anti-Stokes Raman spectroscopy by use of a sodium-seeded flame

Abstract

A common experimental problem with rotational coherent anti-Stokes Raman spectroscopy (CARS) is undesired spectral interference that is due to stray light from the primary laser beams. Also, for the most developed approach, dual-broadband rotational CARS, practical measurements often suffer from stray light interference from the narrow-band laser, inasmuch as the CARS signal is produced inherently in the spectral vicinity of the narrow-band laser beam. An optical filter does not provide a sufficiently sharp transmission profile, thus leading to signal loss and spectral distortion of the rotational CARS signal. An atomic filter consisting of a sodium-seeded flame is presented here as a solution to the problem, and its usefulness was demonstrated in dual-broadband rotational CARS experiments.

Linewidth modelling of C2H2N2 mixtures tested by rotational CARS measurements

“…Apertures were used to minimize the influence of stray light from the probe laser, which presents a specific problem for confined combustion environments or measurement cells. 15 Additionally, a polarization technique and effective filtering in a double monochromator, discussed in detail by Beyrau et al, 16 helped to minimize the stray light produced by the cell windows. The signal was then dispersed by a 0.85-m double spectrometer equipped with two gratings of 2400 grooves/mm.…”

Precision of single‐shot dual‐broadband rotational CARS thermometry with single‐mode and multi‐mode Nd:YAG lasers

“…The technique of interest here is dual-broadband pure rotational CARS (DB-RCARS), 2,3 which has been applied for thermometry and also for concentration measurements in various flames, 4,5 spark-ignition engines 6 -10 and in a gas turbine. 11 The DB-RCARS method is especially well suited for temperature measurements in the range of 300-1500 K, with a relative uncertainty in evaluated temperatures from averaged spectra of 1-3%, 12,13 which is related to the strong temperature dependence of the rotational S 0 -branch spectrum in this range of temperatures. At higher temperatures the relative uncertainty increases, which to a large extent is related to a lower spectral sensitivity to a change in temperature and lack of accurate linewidth data.…”

Development of rotational CARS for combustion diagnostics using a polarization approach

“…The measurement data are compared to the analytical results for the non-resonant and resonant signal intensities calculated using Eq. (6). An intensity of 1 corresponds to the signal intensity with parallel polarizations and a = 0 for all cases.…”

“…[1][2][3] and references therein. The technique has been used for nitrogen thermometry at a variety of conditions, also in more challenging environments such as extremely high pressures [4], sooting flames [5], gas turbine exhausts [6], and internal combustion engines [1,7,8]. Moreover the technique has been developed for relative concentration measurements of oxygen [9,10], carbon monoxide [11], carbon dioxide [12,13], and acetylene [14].…”