Have you heard of photoacoustics?

Photoacoustics is not the most commonly known phrase when it comes to CBRN detection but it is this technology that could allow first responders to detect a variety of chemical agents. The detector was developed by a US Army researcher, it uses a laser and a series of sensitive microphones to stimulate and then detects specific sound waves generated by a material when it absorbs light.
Kristan Gurton, the scientist behind the technique, said that this is a relatively cheap technology and can be used to aid both military and civilian responders to identify harmful gases.

Source: BioPrepWatch