Spectrophotometric refractometer

The device

SpectroRef is the commercial name of HEOS spectrophotometric refractometer, a new type of refractometer for fluids, based on a patented technology of HEOS Photonics. It has been designed to allow accurate refractive index measurements by means of any commercial spectrometer.

Spectrophotometers are among the commonest optical instruments in scientific laboratories. Although many variants exist, they all provide the same type of information, i.e. sample transmittance (or absorbance) vs. wavelength.

SpectroRef consists in standard-size spectrometer cuvette containing a specially-designed diffractive optical element. When a fluid is placed in the SpectroRef cuvette, a normal acquisition of its transmittance spectrum can immediately provide the value of the fluid refractive index.

The measurement process

1. Spectrometer calibration: spectrometer is calibrated without cuvette; transmittance is 1 over the whole spectral range.

   

2. Reference measurement: the empty SpectroRef cuvette is placed in the light path; a diffraction notch is now visible in the low-wavelength region of the tramsittance spectrum, due to the SpectrRef diffractive optical element.

   

3. Refractive index measurement: the investigated fluid is poured into the SpectroRef cuvette; the diffraction notch red-shifts and the fluid refractive index is immediately calculated as the ratio of the peaks' positions.

   

SpectroRef features

Some important features of SpectroRef are:

• typical resolution of 0.5×10^-3 (dependent on the used spectrometer);

• possible implementation of wavelength dependent measurements by allowing rotation of the diffractive optical element;

• real-time measurements and possibility to “modify” the investigated fluid during measurements;

• low cost accessory for commercial spectrometers;

• compatible with standard spectrometers, in the UV, visible and IR spectral range, provided that a properly designed diffractive element is used.