Optical Visualization of Rapid Dynamics along with an Acoustic Spectrum

It is difficult to visualize two or more invisible phenomena independently or separately through phase imaging from the same field of view due to their overlapping modulation to the illumination light beam. However, the phase modulation of the light beam due to rapid dynamics and acoustic field could be separated by the spatial partitioning of the field of view when an additional acoustic spectrum is to be recorded. This spatial partitioning can be achieved either by using the large diameter of the object beam or by using dual object beams in a holographic phase imaging optical setup. In the purview of the above facts, we report a simultaneous visualization of the acoustic spectrum and rapid dynamics of the same phenomenon by using high-speed parallel phase-shifting holographic phase imaging. The recorded field of view of high-speed phenomena can be suitably divided into two areas corresponding to two independent features. We present the results of an electric discharge recording at very high speed, which successfully demonstrates the optical visualization of the acoustic spectrum up to the ultrasound range as well as the rapid dynamics of the electric plasma in terms of an electron avalanche and afterglow vortex formation from the same recording. Due to the visualization of additional acoustic spectrum, the use of bulky and additional digital microphone devices can be avoided in several high-speed phenomena, where both features are required for the study.