X-ray intensity fluctuation spectroscopy by heterodyne detection
Heterodyne measurements coherently mix a reference signal with the signal from a sample, giving access to relative phase. A demonstration experiment shows how the local microscopic velocity in a rubber relaxes after stretching. Heterodyning gives an oscillatory intensity leading to a map, in reciprocal space, of how the velocities of the filler particles in the rubber evolve. The method distinguishes between mechanical relaxation and the local motion of the aggregates. The resulting dynamics appear to be related to a recently recognized characteristic of crowded systems, jamming.
F. Livet, F. Bley, F. Ehrburger-Dolle, I. Morfin, E. Geissler and M. Sutton
![[heterodyne detection]](https://www.iucr.org/__data/assets/image/0012/4062/ml5220.gif)
Oscillatory behavior of the speckle correlation function for various angles between the diffraction vector and the drift direction (velocity: 1.5 nm/s) of the relaxing rubber. The frequency of this oscillation is the Doppler shift of the X-rays scattered from the rubber
