Dynamic light scattering DLS is used to determine the size distribution and movement of small particles in suspension or polymers in solution. Coherent light passes through the sample between two polarizers and the speckle pattern is recorded. The dynamic information of the particles is derived from an autocorrelation of the intensity trace in the recorded images.
The light scattering depends on the size of the particles relative to the wavelength of light and visible light sources are very suitable for particles ranging in size from nm up to mm. In addition, the wavelength of the laser source should be within the sensitivity range of a detector and be outside the absorption region of particles in suspension/solution. Besides the importance of the wavelength, the power level and intensity noise (rms) of a laser need to be considered. Since low concentrations give the most accurate results, the intensity of scattered light is typically relatively weak and thus higher power lasers are often used (200 mW). Ultimately, the scattered light intensity variations are measured, and therefore the intensity noise of the laser (rms) determines the accuracy of the measurements and is thus the most important specification for the laser.
At HÜBNER Photonics our broad portfolio of low noise Cobolt lasers with different power levels and many wavelengths makes them are perfectly suited to DLS measurements.