The difference between the Conventional Design and the Reverse Fourier Design is that in the Reverse Fourier Design the laser beam is moved through a focusing lens (the so-called “Fourier-Lens”) and the convergent laser beam moves through the measuring cell. 35 years ago, FRITSCH was the first company in the industry to bring a revolutionary alternative to the conventional design onto the market in the form of laser diffraction in a convergent laser beam: By positioning the Fourier lens in front of the measuring cell, a convergent laser beam passes through the measuring cell. The design allows covering a wide measurement range.įigure 1. However, the main drawbacks regard the limited capability of measuring large scattering angles and very small particles. One of the benefits of this setup is the fact that even thick measuring layers can be used, which is advantageous especially with aerosols. The conventional design is such that the measuring cell is moved in a wide, parallel laser beam and the scattered light is directly depicted behind the measuring cell, with a lens on an angle-resolving semiconductor detector. The Reverse Fourier Design is the design used in the FRITSCH Laser Particle Sizers ANALYSETTE 22. The Conventional Design and the Reverse Fourier Design are explained below. The central advantage of lasers is the high light intensity and excellent beam quality, which is very important for the accurate measurement of the scattered light. In most cases, a laser is utilized as a light source, but several manufacturers use LED’s or conventional light sources. If the scattering particles become smaller, a point will be reached, where the intensity of the scattered light is the same in all directions. The lower obtainable measuring range of the static light scattering is defined on the basis of the scattering processes. For a large number of instruments, the upper measurement range has been set at 3.8 mm. The stability and adjustability of the optical setup depend on the capability to separate the diffracted light of these small angles from the undiffracted laser beam. Limitations of the TechnologyĪs large particles result in small diffraction angles, it is possible to measure the smallest diffraction angles consistently because of the upper measurement limit. Based on this anisotropic intensity distribution and with the aid of suitable scattering theory, the particle size can be determined. The sample material is irradiated with a light beam and the scattered light intensity is measured in as many directions as possible. “Static Light Scattering”, “Laser Scattering”, “Laser Diffraction” and “Laser-Granulometry” are interchangeably used to refer to the same particle size determination technology.

The instrument is therefore ideal for production and quality control purposes as well as for research and development applications. All these features are now available in one single instrument which is capable of analyzing particles whose size can vary between 10 nm to the millimeter range. They include simple operation, short analysis time, repeatability and reliability, comparable results, cleverly designed dispersion units, and fully automatic analysis. Particle size measurement with sophisticated laser technology ensures several advantages. Sponsored by FRITSCH GMBH - Milling and Sizing Mar 1 2012

Particle sizer