LED-based NIR spectrometer module for hand-held and process analyser applications

Abstract This paper discusses an electronically scanned, small size 32-wavelength NIR spectrometer unit developed for use as a building block in hand-held composition meters as well as in spectroscopic sensors for process automation. The design relies on a linear LED array light source and a fixed grating monochromator. The benefits of the LED spectrometer unit are a highly accurate wavelength scale, with fixed precalibration for subnanometer tolerances and compatibility with a wide operating temperature range, thanks to internal temperature stabilisation. A series of LED spectrometer modules was manufactured for short wave near infrared (SW-NIR) specifications, covering the range from 832 to 1048 nm and a testing program was arranged to characterise typical performance and the spread of the key optical parameters. Potential applications for this SW-NIR wavelength scale can be seen in food, agricultural and petrochemical analysis. The design can also be modified for other wavelengths, for which LEDs are currently available, i.e. from 400 nm to beyond 2 μm, which will further widen the scope of possible applications in the field of NIR spectroscopy and colour analysis.