Mid-IR Spectrometer: Infrared Absorption “Finger-Print” Detection Application Note

Mid-IR regime is proven to have rich absorption “finger-prints” of materials, demonstrated by benchtop measurement tools, such as Fourier Transform Infrared Spectrometer (FTIR). Wavelength Opto-Electronic (WOE) has established the capability to design and build a portable absorption spectrometer in this regime. The primary objectives are rapid on-site identification of materials by users with minimal training.

Operation Principle

The principle of the spectrometer is based on reflection-based infrared spectroscopy as shown in Figure 1. The Mid-IR spectrometer consists of a) a light source and detector unit, b) a flexible sensor head, and c) a graphical user interface (GUI) for operating, controlling, and processing acquired data.

Mid-IR Spectrometer 1
Figure 1. Mid-IR spectrometer principle

The key specifications of the Mid-IR spectrometer are listed below. Compared with similar portable products in the market, our developed device has a wider spectral range.

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Table 1. Key specifications of Mid-IR spectrometer

The reflective fiber probe is made from chalcogenide glass. The main challenge in its design is the efficient coupling in the illumination and collection beam as shown in Figure 2.

Mid-IR Spectrometer 5
Figure 3. Spectrometer and its fiber probe

The overall measurement device and the fabricated fiber probe are shown in Figure 3. The detector is calibrated using the NIST traceability testing target. The spectral coverage can be tuned by choosing alternative LEDs. The spectral resolution can be customized by choosing different stepper motors.

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Figure 3. Spectrometer and its fiber probe


The portable Mid-IR spectrometer can be used in various applications, such as:

  • Food quality analysis
  • In-situ monitoring for process control
  • Remote analysis of gases and vapors
  • Investigation of pollutants

This device also offers a platform to carry out database development and artificial intelligence-based spectral training in the Mid-IR regime.

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