Development of near infrared spectrometer for gem materials study

摘要

Most of gem materials can be characterized by infrared absorption spectroscopy. Normally, mid-infrared absorption technique has been applied for investigating fundamental vibrational modes. However, for some gem materials, such as topaz, NIR is a better choice due to differentiation. Most commercial NIR spectrometers employ complicated dispersive grating or Fourier transform techniques. In this work, we developed a filter type NIR spectrometer with the availability of high efficiency and low-cost narrow bandpass NIR interference filters to be taught in a physics laboratory. The instrument was designed for transmission-mode configuration. A 50W halogen lamp was used as NIR source. There were ten NIR filters mounted on a rotatory wheel for wavelength selection ranging from 1200.1-650 nm with steps of 50 nm. A 1.0 mm diameter of InGaAs photodiode was used as the detector for the spectrometer. Hence, transparent gem materials can be used as samples for experiment. Student can learn vibrational absorption spectroscopy as well as Beer-Lambert law from the development of this instrument.