Wavelength Calibration Source for Low Budget Spectrometers

Overview

The goal of this project was to develop a low-cost spectrometer suitable for demonstration experiments and educational programs. The price point of about $50, easy to source components, and 3D-printed mounts make the design economically accessible. To enable the spectrometer to perform quantitative measurements, it is necessary to perform a wavelength calibration. Professional wavelength calibration equipment requires an investment that is about equal to the total cost of the spectrometer. This study describes low-cost calibration sources. To perform a wavelength calibration, the light source has to provide a set of spectral maxima spread across the range of wavelengths accessible to the spectrometer. This investigation explored multiple low-cost wavelength calibration sources including: LEDs with a single emission maximum in the ultraviolet, blue, green, red and infrared parts of the spectrum; a 650nm wavelength class IIIa laser diode, and a set of fluorescent light bulbs of different colors. A 3D-printed enclosure and mounts were built for various light sources in order to perform reliable measurements with the spectrometer and a professional Ocean Insight, Flame VIS/NIR fiber spectrometer. Measurements performed with the professional spectrometer confirmed standard fluorescent light bulbs as a viable source to calibrate the blue and green parts of the visible light spectrum. This was based on mercury emission lines present in all bulbs independent of color temperature. A laser diode was used to estimate the spectral resolution of the spectrometer with about 4nm, which is suitable for research that requires moderate spectral resolution only. The calibration accuracy achieved with LEDs was verified with a Mercury/Argon calibration source and found to be better than 5nm. Ten LEDs of the same color from two different sources determined the variation of the spectral peak to be similar to the resolution of the homemade spectrometer. This allows the posting of the measurements of LED spectra alongside with the design of the calibration source on the internet to avoid the future need for professional equipment. The results confirm the possibility of low-cost wavelength calibration of the NHAS spectrometer and similar do-it-yourself devices.