Compact, Self-Aligned Focusing Schlieren System

Abstract

A novel compact, self-aligned focusing Schlieren system is presented that eliminates the need for a separate source grid and cutoff grid. A single grid element serves to both generate a projected source grid onto a retroreflective background, and to act as the cutoff grid for the reflected light. This is made possible by manipulating the polarization of the light through the system. The use of only a single grid element eliminates the need to create a cutoff grid that is perfectly matched and scaled to the source grid, and removes the need to align the source and cutoff grids to each other. The sensitivity to density objects is adjustable with the use of a polarizing prism. Images obtained with this system show similar operation to existing focusing Schlieren systems, but with much reduced complexity and setup time. Images taken with acrylic windows placed nor-mal to the optical axis further demonstrate the system’s utility for wind tunnel measurements.