Air is a mixture of several gases or molecular compounds whose composition both affects and provides insight on the climate, human health, and industrial processes. For example, greenhouse gases warm up the atmosphere, carbon monoxide is lethal at high concentrations, and emissions from combustion plants reveal the efficiency of the burning process.
Light is an exceptional tool for measuring the composition of air reliably and in real-time. The simplest optical measurement is based on the attenuation of laser light in the investigated gas sample. However, the measurement is restricted to a single molecular compound because the light emitted by a laser has only a single color. The measurement technique developed in Mikkonen’s work has two major differences compared to this simple approach.
Instead of a single-color laser, Mikkonen utilizes “a white laser” whose light contains several colors, and which enables simultaneous measurement of several molecular compounds. Moreover, instead of light attenuation, his technique focuses on the light-induced changes in the gas mixture that permit the measurement of extremely low gas concentrations from a small amount of sample. The technique is based on the periodic illumination of the gas sample resulting in periodic temperature and pressure changes in the sample, essentially producing a sound wave.
“The measurement system developed in this work causes specific molecular compounds in a gas mixture to produce characteristic sounds, which are listened with a microphone developed for this purpose, tells Tommi Mikkonen.
May help in detecting chemical weapons
One of the most promising applications for the technique is the detection of gas-phase chemical warfare agents, which was experimentally demonstrated in this work together with the Finnish Institute for Verification of the Chemical Weapons Convention from the University of Helsinki.
“Reliable, sensitive, and fast analysis of field samples limited in quantity is essential in the measurement of chemical weapons. The technique developed in the work is extremely suitable for this task,” says Tommi Mikkonen.
The development of this unique technique continues in several research groups around the world.
Tommi Mikkonen is from Tampere and currently works as a researcher at the University of Helsinki.
Public defence on 28 April
The doctoral dissertation of M.Sc. (Tech) Tommi Mikkonen in the field of physics titled Fourier Transform Photoacoustic Spectroscopy with Broadband Lasers will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University on Friday 28 April 2023 at 12 o’clock at Hervanta Campus in the auditorium TB109 of the Tietotalo building (Korkeakoulunkatu 1, Tampere). The Opponent will be Professor Vincenzo Spagnolo from Politecnico di Bari in Italy. The Custos will be Professor Juha Toivonen from the Faculty of Engineering and Natural Sciences, Tampere University.
The dissertation is available online.
The event can be followed via remote connection (Panopto).
Photo: Emilia Kousa