Stirling-based Cascade Technologies is developing an explosive sniffer that it claims can detect parts-per-trillion concentrations.

“At the lab, we were sent a sample of explosives in a glass phial in an aluminium package, and that package had been through the post,” company CEO John Fuller told Electronics Weekly. “We could detect the explosives without opening it.”

The firm’s speciality is quantum cascade lasers (QCLs) which can be made to emit in the mid-infrared. “Mid infrared tends to be where all the interesting gasses have absorption bands,” said Fuller.

QCLs rely on physical dimensions within a semiconductor structure.

By applying a fast high-current pulse, Cascade Technologies causes the laser to heat briefly. The resultant thermal expansion and cooling contraction ‘chirps’ the output across a wavelength band.

“We can use up to four [slightly different] lasers to cover a wider band,” said Fuller.

Detection is “tens of microseconds” once a sample is in the chamber, claimed Fuller.

The firm is offering a complete sniffer module with laser sources, chamber, optics, infrared detector and software which compares measurements with a library of absorption profiles. “We have a patent that covers the whole system,” said Fuller.

A chemical ‘fingerprinting’ system could take the form of a hand-held portable screening unit, as well as fixed in: airport portals or carousels; post rooms; and check points, said Cascade. Poisons and narcotics could also be detected.

The firm is based at the Stirling University Innovation Park.