High-speed digital focusing Schlieren techniques

Schlieren imaging is a powerful visualization technique for investigating weak phase objects. The mirrors or lenses used in traditional knife-edge schlieren systems significantly limit its field of view. Grid-based focusing schlieren systems eliminate this limitation by applying source and cutoff grids which extend the field of view to several meters. However, alignment accuracy between source grid and cutoff grid is crucial for system sensitivity. Complex opto-mechanics are usually required for better results. This paper introduces a compact, portable focusing schlieren systems designed for ease of use without excessive alignment requirements. The system employs a digital display to generate the source grid and uses associated software to calculate the grid pattern, with calibration being completed in tens of seconds. Furthermore, we have built high-speed focusing schlieren systems using different high-speed cameras. With customized display unit, the system can take videos as high as 10 million frames per second (fps), with 10 ns minimum exposure time. The use of commercial camera lenses further allows the system to accommodate different imaging tasks without requiring extensive redesigns.