Multi-Tau Pulsed Illumination Differential Dynamic Microscopy with 80 $μ$s Resolution

Abstract

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 $μ$s is achieved, limited by the dead time of the camera electronics. 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.