What is NIR and SWIR Spectroscopy?

NIR (Near-Infrared) and SWIR (Short-Wave Infrared) spectroscopy are powerful analytical techniques used in a wide range of industries, including pharmaceuticals, agriculture, food and beverages, environmental and materials science. These non-destructive methods go beyond identification of the molecular composition of samples and can give information on physical properties and material characteristics of complex substances through glass and plastic and deep into biological tissue.

What is NIR and SWIR Spectroscopy?

NIR Spectroscopy covers the wavelength range 700 – 2500 nm and SWIR from 700-1700nm, approximately.

Near-Infrared (NIR) spectroscopy involves the probing of the sample with near-infrared light measuring absorption, emission, reflection or diffuse reflectance of light. It is ideal for identifying functional groups and quantifying compounds. In NIR spectroscopy the bands are from overtones and combinations of the fundamental vibrational modes. They are generally O-H, N-H and C-H stretching modes. NIR spectroscopy is often employed in qualitative and quantitative analysis, as it can rapidly identify compounds. The main advantage is little sample preparation is needed. Measurements can be made from samples in glass beakers and by inserting fibre optic probes. This makes the technique very suitable for monitoring manufacturing processes and QA testing. [1]

Short-Wave Infrared (SWIR) spectroscopy, covers the shorter wavelength end of NIR, ranging from 700 nm to 1700 nm - the infrared region closest to the visible spectrum. Because silicon sensors are limited to 1100 nm due to their optical bandgap, InGaAs detectors such as Andor iDus are required. SWIR has applications which are impossible with visible light, for example it can see through silicon, glass, coatings and plastic packaging and can easily detect changes in water content. It is therefore used in high precision product inspection, surveillance, sorting, packaging, filling, and process control.

Industrial Applications of NIR and SWIR:

Pharmaceuticals: NIR and SWIR spectroscopy play a crucial role in pharmaceutical manufacturing, ensuring the quality, purity, and consistency of drugs. NIR is fast, non-destructive and non-contact so can be used in-process. It aids in raw material identification, and real-time process monitoring of tablets. SWIR is advantageous for content uniformity testing and moisture content.
Agriculture: There are many applications such as optimizing crop health, quality control of animal feed, nutrient levels in crops and feeds and detecting diseases. The sensitivity of SWIR to water means that detecting the ripeness and dryness of crops can easily be used for sorting produce.
Food and Beverages: In the food industry, NIR and SWIR spectroscopy assist in assessing nutritional content, detecting adulteration, and determining the freshness of products and unearthing pests, diseases and toxins. These techniques enhance the quality control processes. Examples of use are in milk, beer and wine production.
Environmental Monitoring: NIR and SWIR spectroscopy help environmental scientists to analyse soil and water samples, identifying pollutants, and monitoring ecosystem health. Marine macroplastics have been studied with NIR and SWIR [2] identifying PET bottles, PP ropes and PE cups.
Materials Science: Researchers utilise NIR and SWIR spectroscopy to investigate materials' chemical compositions, characterise polymers, and study mineralogy, gemmology and in precious metals exploration. SWIR is widely used in geological prospecting [3]. NIR spectroscopy measures film thickness and optical properties of nanoparticles and optical coatings.

The advantages of these spectroscopies for industry are:

They are non-destructive and non-invasive
You can achieve rapid results with minimal sample preparation – the sample can be put into a glass beaker or vial.

There are a multitude of applications across many industries
They are highly sensitivity to molecular structures
And you have real-time process monitoring capabilities – a fibre optic can probe the sample.

Applications in Physical Science:

Material Science and Characterization: NIR and SWIR spectroscopy play a pivotal role in studying the molecular and atomic structures of materials. They aid in identifying unknown substances particularly very complex mixtures, rapidly assessing material purity. They are useful in studying physical properties of polymers such as porosity, surface area and particle size [4] and investigating defects in crystalline structures.
Spectroscopic Imaging: These techniques enable researchers to map the distribution of specific components within a sample, providing valuable insights into material heterogeneity and composition. The shorter wavelengths have increased non-invasive penetration into biological materials [5].
Semiconductor Research: SWIR spectroscopy is particularly valuable in semiconductor research to analyse semiconductor devices, to identify impurities and defects, and optimise performance.
Photovoltaic Studies: NIR and SWIR spectroscopy contribute to the investigation of solar cells, helping to enhance their efficiency and understand the underlying physical processes. Both spectroscopies are ideal for examining solar panels.
Surface Science: These spectroscopic methods are used to study surface phenomena, such as adsorption, desorption, and chemical reactions occurring at the interface between materials. Applications include catalysis of fuel in vehicles and defence materials.
Biomedical Applications – NIR and SWIR are being increasingly used in biomedical applications from identifying lung cancers and skin tumours to diagnosing Type 2 diabetes. [6]

Major advantages for use in scientific research are:

- Non-destructive and non-invasive analysis, preserving sample integrity

- Rapid data acquisition and real-time monitoring capabilities

- High sensitivity to molecular vibrations and atomic interactions

- Versatility across numerous physical science disciplines

- Enables precise material characterization and identification

Conclusion:

NIR and SWIR spectroscopy play an essential role in factory, farm and food processing and are a valuable source of information in the toolkit of physical scientists. They unlock a deeper understanding of materials and their properties. With their ability to provide non-destructive and real-time analysis, these techniques have revolutionised research in fields such as material science, semiconductor physics and surface science. As technology continues to advance, NIR and SWIR spectroscopy will undoubtedly pave the way for further discoveries and innovations in the fascinating world of physical science.

[1] https://www.sciencedirect.com/topics/chemistry/nir-spectroscopy

[2] Spectral reflectance of marine macroplastics in the VNIR and SWIR measured in a controlled environment | Scientific Reports (nature.com)

[3] https://iopscience.iop.org/article/10.1088/1755-1315/17/1/012256

[4] Near Infrared Spectroscopy for Polymer Research, Quality Control and Reaction Monitoring - N. Heigl, C.H. Petter, M. Rainer, M. Najam-ul-Haq, R.M. Vallant, R. Bakry, G.K. Bonn, C.W. Huck, 2007 (sagepub.com)

[5] Near-infrared spectroscopy and hyperspectral imaging: non-destructive analysis of biological materials - Chemical Society Reviews (RSC Publishing) DOI:10.1039/C4CS00062E

[6] Optical Spectroscopy for non-invasive disease diagnostics- Oxford Instruments (oxinst.com)