Bench-top Instruments

Bench-top laser diffraction instruments became practical with the advent of high
intensity, reasonably priced lasers and sufficient computing power to process
the scattered light data. Once these barriers to market entry were eliminated
the advantages of laser diffraction over other techniques were apparent: speed
of analysis, application flexibility, small particle accuracy, and ease of use. The
ability to measure nano, micro and macro-sized powders, suspensions, and emulsions, and to do it within one minute, explains how laser diffraction displaced popular techniques such as sieving, sedimentation, and manual microscopy.

Such an instrument consists of at least one source of high intensity, monochromatic
light, a sample handling system to control the interaction of particles and incident light, and an array of high quality photodiodes to detect the scattered light over a wide range of angles. This last piece is the primary function of a laser diffraction instrument: to record angle and intensity of scattered light. This information is then input into an algorithm which, while complex, reduces to the following basic truth:

LARGE PARTICLES SCATTER INTENSELY AT NARROW ANGLES

SMALL PARTICLES SCATTER WEAKLY AT WIDE ANGELS

The algorithm, at its core, consists of an optical model with the mathematical
transformations necessary to get particle size data from scattered light. However,
not all optical models were created equally.