Detecting several gases at once is crucial in areas such as environmental monitoring, industrial physics and fault diagnosis in electrical equipment. Methane is a key sign of natural-gas leakage, while acetylene, can indicate high-temperature faults such as arcing in transformer oil.

The challenge right now is that many sensitive gas sensors either need separate detectors for each gas or measure gases one after another, which means they cannot capture truly simultaneous changes.

A team of researchers from the Harbin Institute of Technology in China have recently developed a new approach using light-induced thermoelastic spectroscopy, or LITES.

In this method, gas molecules absorb modulated laser light resulting in a small amount of heating. This in turn causes tiny mechanical vibrations in a quartz tuning fork. These vibrations are then converted into an electrical signal.

The clever part in the new work is a technique called orthogonal phase modulation. Two lasers are modulated so that their effective signals act orthogonal to each other in signal space. A lock-in amplifier can then split the combined tuning-fork signal into two independent outputs, one for methane and one for acetylene.

The signal separation is described using Lissajous figures, which are patterns produced when two vibrations combine. When the two signals are exactly orthogonal, the unwanted mixing between channels remains very low.

After averaging, the detection limits reach 0.32 parts per million for methane and 0.29 parts per million for acetylene – this is good sensitivity but not record-breaking.

The significance of the work lies not in the detection limit, but the new method. If this phase-separation approach can be extended beyond two gases, future instruments might monitor several chemical species with fewer detectors, fewer demodulation channels and less hardware complexity.

That could have big consequences for industrial safety, greenhouse-gas monitoring, transformer health, combustion diagnostics and enclosed-space gas alarms. The next step would be showing that the method remains stable outside controlled lab conditions and in more complex gas mixtures.