FTIR Spectroscopy

Keit FTIR ATR Dip Probe Tip

Fourier Transform Infrared (FTIR) spectroscopy enables material identification by measuring the amount of light in the mid-infrared region absorbed at the molecular level. Specific molecular bonds absorb light at specific frequencies. Different compounds have different absorption fingerprints, which arise due to the unique combination and relative strengths of each compounds’ absorption frequencies.

FTIR spectrometers pass light through the sample of interest, splits it into two beams and introduces a path length difference before re-combining the beams to generate an interference pattern. A Fourier transformation of the pattern yields the constituent wavelengths of the original input beam – and thus the chemical fingerprint is identified.

Orange-Tri Product Information

Keit has developed the IRmadillo™ as a rugged FTIR spectrometer based on a novel optical design. The spectrometer’s structural simplicity results in a uniquely compact and robust device for operating in tough manufacturing environments. Vibration tolerant, the Keit FTIR was originally developed to be fitted to a satellite.  The resulting qualities have made the IRmadillo™ FTIR spectrometer an ideal analytical instrument for process monitoring and control for industrial applications.

For industries that involve highly volatile products, download the spec sheet for Keit’s IRmadillo™ FTIR spectrometer for potentially explosive (Ex) environments.

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Orange-Tri Current Standard: Michelson Interferometers

Current standard FTIR instruments, based on the Michelson interferometer, reflect a beam of light off of a moving mirror creating an instrument that is sensitive to vibration and therefore not reliable for direct use in manufacturing environments (Figure 1 below).

Orange-Tri The rugged IRmadillo™ FTIR Spectrometer: Design Advantages

Keit uses a novel optical design based on the Sagnac interferometer with no moving parts making it inherently more stable (Figure 2 below).

Michelson FTIR light path

Figure 1: Michelson Interferometer – Example light path and internal design showing moving mirror arm creating an instrument that is sensitive to vibration and shock.

Keit FTIR light path

Figure 2: The Keit rugged IRmadillo™ FTIR spectrometer – example light path and improved internal design demonstrating no moving parts producing an extremely stable instrument able to operate in high-vibration working environments.

In the current Michelson standard, light from a source (1) is split into two beams by a beamsplitter optic (2) and directed along two orthogonal arms where it reflects off a mirror (3, 4) and is returned to the beamsplitter. By changing the position of one of the mirrors (and hence the length of the arm), the various wavelengths of light in the input light source experience different optical path lengths in each arm and interfere constructively or destructively with one another when they return to the beamsplitter. This interference pattern is then measured with respect to time on a broadband detector (5) to produce a spectrum (interferogram).

Because this design relies on delicate, finely adjusted moving parts, any vibration, shock or thermal expansion that differentially impacts the two path lengths will introduce significant noise in to the interferogram. Most industrial environments have some level of vibration or shock and this interferes with the smooth operation of the Michelson mechanism.

Unlike alternative FTIR spectrometers, the IRmadillo spectrometer uses a beamsplitter (1) to direct light in both directions around a loop interferometer (2) that – crucially – contains no moving parts. The whole interferogram is formed on a detector array (3) at the same instant. This configuration means that noise or vibration affects both beams equally and is therefore cancelled out. This is the key making data collected by the Keit instrument exceptionally robust.

The IRmadillo FTIR spectrometer is also smaller and lighter than most FTIRs, resulting in an ease-of-use in even the most restricted test environments. The toughness of the instrument also allows for it to be used over a wide range of temperatures and operating environments (including outdoor plants) making it suitable for use where other instruments fall short. The cutting-edge design and inherent structural simplicity result in a uniquely compact and robust device for process monitoring and control in manufacturing environments.