The digital, fully automatic spectral refractometer ATR-L consists of an electronic unit separated from the stainless steel measuring unit. Dispersion measurement at 7 wavelengths over the full visible range. A sample volume of 0,3 ml is sufficient for measuring. The refractometer is equipped with a Peltier thermostat (no external water bath/thermostat necessary).

Multiple wavelength digital refractometer for dispersion measurements.

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 digital multiple wavelength refractometer of SCHMIDT + HAENSCH is based on CCD-sensor detection of the critical angle of total reflection. This is done sequentially for all LEDs (colours) and displayed as refractive indices according to these wavelengths. SCHMIDT + HAENSCH has the necessary data basis for calibration of such an instrument through research work performed at its premises in Berlin.

Applications

Potential applications will be found in research and development, where the exact knowledge of material properties is of great importance. Further fields of application will also be in the medical research (plastic lenses, contact lenses) and in communication technology (polymer materials, special optical liquids and glues).

The exact knowledge of material properties is of great importance for successful research and development. ATR-L 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 ATR-L can perform valuable services in scientific research and standard ASTM measurements.

The measurement principle of ATR-L 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 ATR-L 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.