Simultaneous multiple time scale imaging for kHz–MHz high-speed accelerometry

Abstract

Fast transient events, such as the disintegration of liquid bodies or chemical reactions between radical species, involve various processes that may occur at different time scales. Currently, there are two alternatives for monitoring such events: burst- or high-speed imaging. Burst imaging at ultrahigh speeds ( ∼ 100 MHz to THz ) allows for the capture of nature’s fastest processes but only for a narrowly confined period of time and at a repetition rate of ∼ 10 Hz . Monitoring long lasting, rapidly evolving transient events requires a significantly higher repetition rate, which is met by existing ∼ kHz to 1 MHz high-speed imaging technology. However, the use of such systems eliminates the possibility to observe dynamics occurring on the sub-microsecond time scale. In this paper, we present a solution to this technological gap by combining multiplexed imaging with high-speed sensor technology, resulting in temporally resolved, high-spatial-resolution image series at two simultaneous time scales. We further demonstrate how the collection of such data opens up the tracking of rapidly evolving structures up to MHz burst rates over long durations, allowing, for the first time, to our knowledge, the extraction of acceleration fields acting upon the liquid bodies of an atomizing spray in two dimensions at kHz frame rates.

High-speed videography of transparent media using illumination-based multiplexed schlieren

“…This separation of Fourier clusters allow for their corresponding signals to be individually reconstructed, by applying a lock-in algorithm and a low-pass filter. The process is described in more detail in 28,[38][39][40][41][42][43] . As more images are stored on the detector the distance between the Fourier clusters will unavoidably decrease, and eventually the size of the applied low-pass filter will have to be decreased to avoid cross-talk between signals.…”

“…The presented approach is based on an intensity modulation-scheme, which is a versatile optical method that is used for several different imaging applications, such as topography 31 , super-resolution microscopy 32 , schlieren 19,20,33,34 , interferometry 35,36 and thermometry 37 . Here we combine its ability to provide schlieren images through phasesensitive analysis 20 with its ability to optically multiplex temporally separated image data 28,[38][39][40] into a powerful imaging concept. Past approaches for image multiplexing using this scheme have thus far been based on quantifying the amplitude of the intensity modulation; to gain schlieren data, we here demonstrate the ability to extract phase information from such multiplexed data.…”