Abstract
The laser schlieren arrangement described in Chapter 2 generates intensity contrast images using a knife-edge. The gradient normal to the knife-edge is highlighted in this approach. Gradients in other directions can be revealed by suitably orienting the knife-edge. This approach is not sufficiently general and one can look for other routes by which gradients can be imaged in one setting. Apart from this disadvantage, the knife-edge suffers from diffraction errors. These difficulties can be circumvented with the help of a graded filter wherein a transparent film with a grayscale imprinted on it is used at the knife-edge location. The film is a generalization of the knife-edge which can be understood as a cutoff filter with two shades, black and white. On a graded filter, the grayscale highlighted by the image can be used to determine the angle through which the light beam has been deflected. Extending this approach further, the grayscale filter can be replaced by a color filter so that a color image is obtained from schlieren measurement. The implication here is that the laser is replaced by a white light source, and the monochrome CCD camera by a color CCD camera. When a color filter is used, the optical elements have to be achromatic. This approach is referred to as rainbow schlieren, and also referred as color schlieren since it generates a color image.
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Panigrahi, P.K., Muralidhar, K. (2012). Rainbow Schlieren. In: Schlieren and Shadowgraph Methods in Heat and Mass Transfer. SpringerBriefs in Applied Sciences and Technology(). Springer, New York, NY. https://doi.org/10.1007/978-1-4614-4535-7_3
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DOI: https://doi.org/10.1007/978-1-4614-4535-7_3
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