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Infrared Laser Spectroscopy At Your Fingertips

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Sensing applications take a big step forward, thanks to a photonic chip spectrometer that delivers the performance of a table-top laboratory instrument

BY Augustinas Vizbaras FROM Brolis Sensor Technology

Developed during the first half of the twentieth century, infrared spectroscopy has established itself as an effective, widely adopted laboratory technique for analysing organic and inorganic compounds. By measuring the interaction of matter with infrared radiation, this form of spectroscopy can identify compositions of substances, determine the presence and absence of chemical species, and offer quantitative and qualitative analysis. When radiation is directed at a substance, the photons that are absorbed have energies coinciding with vibrational frequencies that are molecule specific. Since every different molecule has a unique molecule-specific absorption spectrum, it is possible to identify species and measure their concentrations within a sample.


Figure 1. The basic principles of infrared spectroscopy, when measuring a sample in a transmission configuration. Orientations include: (a) a broadband light source and a static filter, (b) a broadband light source with a tuneable filter, and (c) a tuneable light source. BB short for the broadband light source, Sample is the object under investigation, Filter is the spectral filter/wavelength discriminator, and D is the detector of radiation.

The tremendous insight garnered from infrared spectroscopy has led to the use of spectrometers in numerous applications. This technique is serving in the biomedical sphere, where it is used to analyse biological fluid, tissue and pharmaceuticals; it is deployed in industrial sectors, such as those involving chemicals, bioreactors, petrochemicals and polymer technology; it is valued in environmental settings, providing the likes of gas analysis and pollution monitoring; it is found in the food industry, where it provides trace element detection and unveils composition; and it also serves in agriculture and veterinary applications.

So common is infrared spectroscopy that it is found in every governmental, regulatory or industrial laboratory, providing a gold standard. Note that instrumentation takes many forms, from the universal table-top Fourier-transform infrared spectrometer (FTIR), to different designs of laser spectrometer and Raman spectrometer.

Unfortunately, all these high-end tools are bulky and expensive, restricting their use to the lab. It would be far better to deploy them directly at sites, providing in-line, in-situ monitoring. However, this is too expensive, preventing the opportunity to provide better control over processing and the identification of deviations from intended processes in real-time. Instead, when infrared spectroscopy is used today, it provides results that are offline - and often off-site.