Particle characterization
A particle characterization apparatus is disclosed 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 backscattered light along a detection optical path that intersects the focussed light beam within the sample. The intersection of the light beam and the detection optical path in the sample define a detection region. The apparatus comprises an optical arrangement for varying the volume of the detection region.
1. 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.
2. The apparatus of claim 1 , wherein the optical arrangement for varying the volume of the detection region is operable to vary the light beam width incident on the focussing lens.
3. The apparatus of claim 2 , wherein the optical arrangement for varying the light beam width incident on the focussing lens comprises a beam expander.
4. The apparatus of claim 3 , wherein the beam expander comprises a moveable lens, operable to vary the light beam width incident on the focussing lens with movement of the moveable lens.
5. The apparatus of claim 4 , wherein the beam expander further comprises a fixed lens between the light source and the moveable lens.
6. The apparatus of claim 5 , wherein the beam expander is operable to produce a collimated output beam of variable width.
7. The apparatus of claim 5 , wherein the fixed lens comprises a diverging lens.
8. The apparatus of claim 5 , wherein the fixed lens comprises a converging lens.
9. The apparatus of claim 4 , wherein the moveable lens comprises a converging lens.
10. The apparatus of claim 1 , wherein the focussing lens focuses the detection optical path within the sample.
11. The apparatus of claim 10 , wherein the detection optical path comprises an optical fibre.
12. The apparatus of claim 11 , wherein the optical fibre comprises a single mode fibre.
13. The apparatus of claim 11 , further comprising a coupling lens arranged to couple the detection optical path to the optical fibre.
14. The apparatus of claim 13 , wherein the coupling lens comprises a graded refractive index lens.
15. The apparatus of claim 1 , wherein the converging lens is a fixed lens.
16. The apparatus of claim 1 , wherein the focussing lens comprises a focus tuneable lens.
17. The apparatus of claim 1 , wherein the apparatus comprises a processor for performing the dynamic light scattering measurement.