Refractometers are widely used in food, oil, fuel and other industries to measure the concentration of components in order to monitor and control the fabrication process. They measure the critical angle of total reflection and calculate the refractive index from this value. The refractive index of a substance depends on the wavelength of light and usually increases towards shorter wavelengths.
For a better characterisation of this behaviour, Abbè introduced the so-called Abbè-number which is an arithmetical dimensionless value calculated from measured refractive indices at 486, 546, 656 nm. Nowadays, this is not used frequently any more, since the development of high-resolution refractometers made it possible, to measure refractive index differences of 0.00001 easily. But information regarding refractive index behaviour at other wavelengths is lost, which could give a fingerprint about the material itself. The so-called dispersion shows clear differences for chemically different substances, which do appear more pronounced at short wavelengths than at the longer end of the visible spectrum. This makes it possible to distinguish substances which otherwise are absolutely similar at 589 nm (sodium- wavelength).
Because the modern light sources like LED`s are offering highly directed light of a variety of wavelengths and are simple in use, it was possible to develop robust multi wavelength automatic refractometer, allowing to perform simple measurements of dispersion. The use of discrete LEDs also makes it possible to implement any combination of customer-specified wavelengths in the instrument and carry out quasi-spectral measurements in almost real time.
The exact knowledge of material properties is of great importance for successful research and development. DSR-λ of SCHMIDT+HAENSCH can be used for example in medical development (plastic lenses, proteins ...) and in the optical communication technology (polymer materials, special optical liquids, glasses and glues). In the petrochemical industry DSR-λ can perform valuable services in scientific research and standard ASTM measurements.
The measurement principle of DSR-λ relies on a complete refractive index measurement at visible wavelengths, which is also sensitive to absorption, leading to a full optical characterisation of the measured substance. For example measuring a fruit juice will not only determine the sugar content but also provide valuable information on colour and turbidity.
The measuring principle of the DSR-λ is similar to DNA analysis giving unique fingerprint-like data for a particular product. Using this fingerprinting characterisation; high quality products like wine, perfumes, alcoholic beverages etc. can easily identified along with possible forgeries.