TEST & MEASUREMENT
Precision gas sensing for demanding process environments
Process control is essential in highly regulated industries. Pharmaceutical and chemical manufacturers must demonstrate but throughout production. Monitoring is therefore embedded into process design rather than added downstream and Process Analytical Technologies (PAT) provide the framework for this approach.
Hamamatsu Photonics UK
T
he objective of PAT is the real-time understanding of critical process parameters, which in many cases depends on accurate analysis of reactants and by- products in the gas phase. This provides direct insights into reaction progress and process stability, and continuous gas measurement enables tighter control, faster interventions and improved regulatory assurance.
manufacturing, gas monitoring includes volatile and semi-volatile organic compounds (VOCs), particularly residual solvents generated during synthesis and recovery. Carbon-containing gases such
as carbon dioxide (CO2) and carbon monoxide (CO), along with reactive species
like ammonia (NH3), are also monitored in processes involving gas-phase reactions or off-gas analysis. In hydrogenation and catalytic systems, analysis of reactor off-gas composition provides continuous insights into reaction conditions within the PAT framework.
Figure 1: Example gas molecules with characteristic absorption bands in the IR spectrum. Optical sensing
Real-time measurement of mixed gas streams requires in-line analytical systems that respond rapidly to process changes and can resolve spectrally overlapping molecular species. Optical gas sensing meets these demands by measuring the absorption of light at characteristic wavelengths, which indicates concentration according to the Beer-Lambert law. Mid-infrared (MIR) sensing, typically spanning 3 to 11 μm, targets the strong fundamental vibrational absorption bands of many industrially relevant molecules such
as VOCs, CO2, CO and NH3. The intensity and spectral separation of these bands enable in complex mixtures. Quantum cascade lasers (QCLs) are especially useful in MIR sensing, due to their tuneable, spectrally precise emission across wide wavelength ranges.
QCLs in process monitoring QCLs are compact semiconductor lasers that operate in continuous or pulsed modes, and emit with extremely narrow linewidths,
28 MARCH 2026 | ELECTRONICS FOR ENGINEERS
typically below 1 MHz. Such spectral resolution is critical for the analysis complex gas mixtures, where absorption lines are narrow and often overlap. QCLs enhance sensitivity through their high-brightness, highly collimated output, enabling detection at ppb levels. Their beam quality also pass gas cells, such as Herriott cells, which the beam multiple times through the sample. The resulting increase in interaction improves absorbance and overall detection sensitivity compared with non-laser MIR sources. In addition to high sensitivity, QCLs also offer fast modulation and rapid wavelength switching which, combined with strong signal levels and low-noise detection, reduce acquisition times and support high-speed gas analysis. This enables conditions for tighter real-time control of critical process parameters.
Challenges to QCL adoption practical factors continue to impact wider
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