Rotational Raman Imaging
Rotational Raman imaging is motivated by an effort to capture spatially resolved measurements of temperature and density in complex fluid environments, such as flames or reactive flowfields. By spectrally resolving the rotational Raman spectra, information of Boltzmann fraction may be obtained for individual species... and hence, species selective, spatially resolved measurements may be made in harsh environments. The ultraviolet laser is paired with two different styles of spectral filter in order to achieve these measurements.
UVFRS Demonstration:The narrow passband imaging filter (see diagram 1) rejects all light that is not coincident with the mercury vapor absorption band, and maintains images as demonstrated in diagram 2.
Scattering of laser light from a Princeton shield is imaged with the laser tuned to three differing spectral locations (as shown by the cartoon below each picture in diagram 2).
The same filter has been used to capture Rayleigh scattering from room air (diagram 3).Raman scattering of individual rotational lines of Oxygen and Nitrogen (diagram 4)
Refractive Imaging Filter (Vapor Prism):
Alternately, a filter capable of spatially resolving multiple rotational Raman lines in one dimension (while spectrally resolving in the other) is achieved by constructing a vapor prism (see diagram 5).
Diagram six is a spatially resolved (in the horizontal) image of pure rotational Raman scattering from ambient carbon dioxide.
Finally, individual lines are just resolvable (diagram 7).