Facts About Laser Diffraction

As a technique of particle size analysis, laser diffraction is widely used and has many advantages. It offers a high level of precision, a fast speed of response, high potential for the repetition of results and a wide measurable particle diameter range. Particle size analysers offer a sophisticated way of measuring particle size and enable incredible insight and understanding of the particles that make up materials used in a range of industries.

Laser diffraction is an important technique for measuring particle size. Here we offer a range of facts about this technique:

• It is also known as Low Angle Laser Light Scattering (LALLS).
• Considered a standard method in many industries because of its ability to characterise particles and for reasons of quality control.
• Huge advances have been made in instrumentation over at least the last two decades.
• The method is founded on the fact that the angle of diffraction is inversely proportional to particle size.
• The instrument consists of a laser (as a source of coherent intense light that has a fixed wavelength), a detector (typically an array of photo sensitive silicon diodes) and a means of passing the sample through a laser beam.

Laser diffraction is so popularly and extensively used because it offers a number of advantages. These advantages include:

An absolute method grounded in fundamental scientific principles – In this method it is not necessary for an instrument to be calibrated against a standard. However, validation of equipment is possible to prove that it is performing to a standard that can be traced.

Wide and dynamic range – In measuring particle size, good equipment will allow the user to measure particles sized between approximately 0.1 and 2000 microns.

Flexibility – Laser diffraction offers new possibilities for measuring materials. It is even possible to measure the paint that is sprayed from a nozzle in a paint booth. The pharmaceutical and agricultural industries are two of the many industries that have benefited greatly from such advances.

Dry powders – Even dry powders can be measured through the technique of laser diffraction. Although this may result in a poorer level of dispersion than if a liquid dispersing medium was used, it is an advance that dry powders can be directly measured. In combination with a suspension analysis, it can support the assessment of the amount of agglomerated material in a dry state.

Liquid suspensions and emulsions – It is possible to use a recirculating cell to measure liquid suspensions and emulsions. This technique promotes a high level of reproducibility and facilitates the use of dispersing agents and surfactants to determine the primary particle size. If it is possible to do so, it is preferable to take measurements in a liquid suspension.

Sample measured – This technique allows for the whole of the sample to be measured. As the sample passes through the laser beam, diffraction is measured for all particles.

Rapid – This technique is so rapid that results can be derived in one minute or less. Feedback can therefore quickly be provided to plants and repeat analyses can also be made quickly.

Repeatable – This technique is highly repeatable and knowing that the results can be relied upon provides peace of mind.

A sophisticated method for determining particle size, laser diffraction is widely used and offers distinct advantages that are beneficial for many industries.