Particle characterization

A particle characterization apparatus comprising:

• a sample cell for holding a sample;
• a light source for producing a light beam for illuminating the sample in the sample cell, thereby producing scattered light by the interaction of the light beam with the sample;
• a focussing lens for focussing the light beam within the sample;
• and
• a detector for detecting the scattered light along a detection optical path that intersects the focussed light beam within the sample, the intersection of the focussed light beam and the detection optical path in the sample defining a detection region, wherein the apparatus comprises an optical arrangement for varying the volume of the detection region and the focussing lens is moveable, so as to vary a location of a focal plane of the light beam and detection optical path in the sample with movement of the focussing lens so as to vary the position of the detection region within the sample;
• wherein the apparatus is operable to perform a dynamic light scattering measurement using an output from the detector;
• wherein the optical arrangement for varying the light beam width incident on the focussing lens comprises:
• a converging lens between the focussing lens and light source causing the light beam to be convergent or collimated at the focussing lens, and a mount operable to move the focussing lens so as to vary the distance between the focussing lens and the converging lens.