Schlierenfotografi

Schlierenfotografi, derived from the German word for "streaks" or "striations," is an optical technique used to visualize and quantify optical inhomogeneities in transparent media. These inhomogeneities are typically caused by variations in refractive index, which can arise from differences in temperature, pressure, or density. The method works by selectively blocking light that has been slightly deflected by these variations, making them visible as dark and light patterns.

The fundamental setup involves a light source, a large concave mirror to collimate the light into a parallel beam, and a second identical mirror to refocus the beam. Placed at the focal point of the second mirror is a knife-edge or a stop. When the medium being studied is uniform, the light passes through without deflection, and the knife-edge is positioned to block this undisturbed light, resulting in a uniformly dark field of view. However, if there are variations in the refractive index, the light rays will be deflected. The knife-edge then either passes or blocks this deflected light depending on its direction, creating visible streaks or schlieren patterns that map the variations in the medium.

Schlieren photography finds applications in various scientific and engineering fields. It is commonly used to study fluid dynamics, such as airflow over aerodynamic surfaces, shock waves, and convection currents. It is also employed in heat transfer analysis to visualize thermal gradients and in optics for testing the quality of lenses and optical components. The technique provides a non-intrusive way to observe and measure these otherwise invisible phenomena, offering valuable insights into the behavior of gases and liquids.