Shadowgraphy

The technique is based on high resolution imaging with pulsed backlight illumination. The measurement volume is defined by the focal plane and the depth of field of the imaging system. This technique is independent of the shape and material (either transparent or opaque) of the particles and allows the investigation of sizes down to the micro scale using an appropriate optical system.
The light source can be a pulsed laser with special illumination optics or a flashlamp, depending on the velocity of the particles. Using a short laser pulse as illumination, it is possible to “freeze” motions of more than 100 m/s. A double pulse laser combined with a double frame camera allows the investigation of size dependent particle velocities.