How DLS Works

• The dark spaces in the speckle pattern produced by light scattering are where the phase additions of the scattered light are mutually destructive. The bright spots of light in the speckle pattern are where the light scattered from the particles arrives with the same phase and interfere constructively.

• The observed signal depends on the phase addition of the scattered light falling on the detector. In example A, two beams interfere and “cancel each other out” resulting in a decreased intensity detected. In example B, two beams interfere and “enhance each other” resulting in an increased intensity detected.