[1][2] DDM is suitable for typical soft materials such as for instance liquids or gels made of colloids, polymers and liquid crystals but also for biological materials like bacteria and cells.
If the image intensity is locally proportional to the concentration of particles or molecules to be studied (possibly convoluted with the microscope point spread function (PSF)), each movie can be analyzed in the Fourier space to obtain information about the dynamics of concentration Fourier modes, independent on the fact that the particles/molecules can be individually optically resolved or not.
After suitable calibration also information about the Fourier amplitude of the concentration modes can be extracted.
The concentration-intensity proportionality is valid at least in two very important cases that distinguish two corresponding classes of DDM methods: In both cases the convolution with the PSF in the real space corresponds to a simple product in the Fourier space, which guarantees that studying a given Fourier mode of the image intensity provides information about the corresponding Fourier mode of the concentration field.
Still, the images are acquired in the real space, which provides several advantages with respect to traditional (far field) scattering methods.
DDA works by subtracting images acquired at different times and taking advantage that, as the delay
A two-dimensional fast Fourier transform (FFT) analysis of the difference images allows to quantify the growth of the signal contains for each wave vector
[2] Equation (1) shows that DDM can be used for DLS experiments, provided that a model for the normalized intermediate scattering function is available.
is determined by calibrating the microscope with a suitable sample, DDM can be employed also for SLS experiments.
[2] Running DDM on a series of frames smaller than the full-frame has been called multi-DDM.
[5] Scattering-based DDM belongs to the so-called near-field (or deep Fresnel) scattering family,[6] a recently introduced family of imaging-based scattering methods.
The near field scattering family includes also quantitative shadowgraphy[9] and Schlieren.
[3] DDM was introduced in 2008 and it was applied for characterizing the dynamics of colloidal particles in Brownian motion.