In:
Applied Optics, Optica Publishing Group, Vol. 59, No. 27 ( 2020-09-20), p. 8293-
Abstract:
Three-beam rotational coherent anti-Stokes Raman scattering (CARS)
measurements performed in highly scattering environments are susceptible to contamination by two-beam CARS signals generated by the
pump–probe and Stokes–probe interactions at the measurement volume. If this occurs, differences in the Raman excitation bandwidth between the
two-beam and three-beam CARS signals can add significant errors to the spectral analysis. This interference to the best of our knowledge has
not been acknowledged in previous three-beam rotational CARS experiments, but may introduce measurement errors up to 25% depending
on the temperature, amount of scattering, and differences between the two-beam and three-beam Raman excitation bandwidths. In this work, the
presence of two-beam CARS sign al contamination was experimentally
verified using a femtosecond–picosecond rotational CARS instrument in two scattering environments: (1) a fireball generated by a
laboratory-scale explosion that contained particulate matter, metal fragments, and soot, and (2) a flow of air and small liquid droplets.
A polarization scheme is presented to overcome this interference. By rotating the pump and Stokes polarizations + 55 ∘ and − 55 ∘ from the probe, respectively, the
two-beam and three-beam CARS signals are orthogonally polarized and can be separated using a polarization analyzer. Using this
polarization arrangement, the Raman-resonant three-beam CARS signal amplitude is reduced by a factor of 2.3 compared to the case where all
polarizations are parallel. This method is successfully demonstrated in both scattering environments. A theoretical model is presented, and
the temperature measurement error is studied for different experimental conditions. The criteria for when this interference may
be present are discussed.
Type of Medium:
Online Resource
ISSN:
1559-128X
,
2155-3165
Language:
English
Publisher:
Optica Publishing Group
Publication Date:
2020
detail.hit.zdb_id:
207387-0
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