Current high-speed imaging technology forces us to make several compromises, one of which is the tradeoff between the imaging speed and the recording duration. Specifically, at frame rates in the MHz to GHz regime, one can typically only record for very short durations (~microseconds). However, if one wishes to record for longer durations (~seconds), existing technology typically restricts the frame rates to the kHz to MHz regime. To alleviate this tradeoff, Kornienko et al. propose a hybrid approach, combining three temporally-offset, nanosecond pulsed lasers and a conventional high-speed camera that can record for long durations at kHz to MHz rates. In one exposure period, the camera records one image from all three temporally-offset pulses, from which three independent frames can be extracted through encoding in the spatial Fourier domain. The relative time delay among the three pulsed lasers can be tuned, depending on the application, leading to high-frame-rate bursts exceeding 10 MHz over long-term recordings at camera-limited frame rates of 10s of kHz. With this unique capability, the authors are able to study the velocity and acceleration fields of complex fluid dynamics of entire fluid injection events. With shorter pulses, this technique could be extended to study even faster events, such as chemical reactions.
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