A Novel Double-Exposure Shadowgraph Method for Observation of Optodynamic Shock Waves Using Fiber-Optic Illumination

摘要

A novel double-exposure shadowgraph method is presented which allows visualization of an expanding shock wave in two time instances on a single image. The method has been developed to study shock waves generated in air during interaction of Er:YAG laser light with water and biological tissues. The shock wave is illuminated by pulsed green laser light coupled into two optical fibers of different lengths to establish two illumination flashes separated by a fixed time delay, An image of the shock wave region, acquired by a digital still camera, exhibits two well separated shock wavefronts. The optical setup is analyzed using a paraxial ray model to explain the observed eccentricity of the two acquired wavefronts and provide guidelines for assembling the set-up.