Abstract
Many important scientific questions in physics, chemistry and biology rely on high-speed optical imaging techniques for their investigations. These techniques are either passive, relying on the rapid readout of photoactive elements, or active, relying on the illumination properties of specially designed pulse trains. Currently, MHz imaging speeds are difficult to realize; passive methods, being dictated by electronics, cause the unification of high spatial resolution with high frame rates to be very challenging, while active methods rely on expensive and complex hardware such as femto- and picosecond laser sources. Here we present an accessible temporally resolved imaging system for shadowgraphy based on multiplexed LED illumination that is capable of producing four images at MHz frame rates. Furthermore as the LEDs are independent of each other, any light burst configuration can be obtained, allowing for instance the simultaneous determination of low- and high speed events in parallel. To the best of the authors’ knowledge, this is the fastest high speed imaging system that does not rely on pulsed lasers or fast detectors, in this case reaching up to 4.56 MHz.
Highlights
Many important scientific questions in physics, chemistry and biology rely on high-speed optical imaging techniques for their investigations
Since the illumination dictates the properties of the time axis, the image series can be tailored from the Hz to the MHz regime or a mixture of both
We have presented a FRAME illumination system based on fast pulsed LED technology, allowing for high spatial resolution transmission imaging on the MHz timescale
Summary
Many important scientific questions in physics, chemistry and biology rely on high-speed optical imaging techniques for their investigations. In 1991 Takeharu Etoh and Kodak invented the Ektapro line of cameras, of which the first one was capable of imaging at a speed of 40 × 103 frames per second (fps) for 64 × 64 pixels (a partial readout scheme on 256 × 256 pixels)[13] This has opened the doors for the development of fast digital passive imaging technology, i.e. imaging where light emitted from an event is recorded on a 2D array of photoactive elements[14]. In general for passive high-speed digital imaging, the necessity of in situ storage makes it difficult to attain high pixel numbers This necessity leads to a trade-off between frame rate, spatial resolution and number of images (sequence depth). The technology currently available for high speed imaging in the MHz regime mainly relies on systems—passive or active—that use advanced and/or expensive hardware
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