Differential dynamic microscopy (DDM) is a digital video-microscopy technique for quantitative measurements of the microscale dynamics in soft condensed matter systems. Here, multi-tau pulsed illumination DDM (MTPI-DDM) is introduced as a method for significantly enhancing the time resolution of DDM. The technique employs simple, low-cost instrumentation comprising a single monochrome digital camera and a single pulsed LED. A timing sequence, following a geometric progression of time lags, is used to generate a "multi-tau" scheme, providing high sampling density at short timescales where dynamics are fastest. In the current implementation, a time resolution of 80 μs is achieved, limited by the dead time of the camera electronics. The validation of MTPI-DDM was performed by measuring the diffusion of 147 nm polystyrene nanoparticles in water. Compared to conventional continuous-wave (CW) DDM, the pulsed approach extends the range of the shortest measurable time lags by nearly two orders of magnitude and enhances DDM signal amplitudes by eliminating motion blur.
Schaub et al. (Mon,) studied this question.