Fig. 1.

Dual-PWS instrumentation, acquisition, and analysis. a Schematic of the Dual-PWS instrumentation. Broadband white light from a light-emitting diode (LED) is passed through a filter to remove ultraviolet (UV) components before being focused onto the sample. The backscattered light is collected, spectrally filtered through a liquid crystal tunable filter (LCTF), and imaged with a charge-coupled device (CCD) camera. b (left) Structural measurements (Σ_s) are collected by acquiring multiple backscattered wide-field monochromatic images across a range of wavelengths (500–700 nm) to produce a three-dimensional image cube, I(λ, x, y), where λ is the wavelength and (x, y) correspond to pixel. Σ_s is extracted by calculating the standard deviation of the spectral interference at each pixel (x, y). (right) Dynamics measurements [${\Sigma }_{\mathrm{t}}^2$, m_f (fractional moving mass), and D (diffusion coefficient)] are collected by acquiring multiple backscattered wide-field images at a single wavelength (550 nm) over a period of time (acquisition time), to produce a three-dimensional image cube, I(t, x, y), where t is time and (x, y) correspond to pixel positions. D is extracted by calculating the decay rate of the autocorrelation of the temporal interference and m_f is calculated by normalizing the variance of the temporal interference (${\Sigma }_{\mathrm{t}}^2$) at each pixel (x, y)