Lecture
This lecture covers the principles of Schlieren visualization, a technique used to visualize variations in refractive index in transparent media. The deflected rays focus to the same point as if they hadn't been diverted, with the deflection proportional to the deviation. By placing a color filter instead of the blade, rays deflected downwards turn blue, while rays deflected upwards turn red. The orientation of the knife blade affects the visualization, as shown in strioscopic images of a helium jet entering a beam.