Using lasers to study explosions

September 03, 2019

WASHINGTON, D.C., September 3, 2019 -- An explosion is a complex event involving quickly changing temperatures, pressures and chemical concentrations. In a paper in the Journal of Applied Physics, from AIP Publishing, a special type of infrared laser, known as a swept-wavelength external cavity quantum cascade laser (swept-ECQCL), is used to study explosions. This versatile instrument has a broad wavelength tuning range that allows the measurement of multiple chemical substances, even large molecules, in an explosive fireball.

The ability to measure and monitor the dramatic changes during explosions could help scientists understand and even control them. Measurements using rugged temperature or pressure probes placed inside an exploding fireball can provide physical data but cannot measure chemical changes that may be generated during the explosion. Sampling the end products of a detonation is possible but provides information only once the explosion is over.

In this work, molecules in the fireball are detected by monitoring the way they interact with light, especially in the infrared region. These measurements are fast and can be taken a safe distance away. Since fireballs are turbulent and full of strongly absorbing substances, lasers are needed.

Using a new instrument built in their lab, the investigators measured explosive events at faster speeds, at higher resolutions and for longer time periods than previously possible using infrared laser light.

"The swept-ECQCL approach enables new measurements by combining the best features of high-resolution tunable laser spectroscopy with broadband methods such as FTIR," co-author Mark Phillips explained.

The study looked at four types of high-energy explosives, all placed in a specially designed chamber to contain the fireball. A laser beam from the swept-ECQCL was directed through this chamber while rapidly varying the laser light's wavelength. The laser light transmitted through the fireball was recorded throughout each explosion to measure changes in the way infrared light was absorbed by molecules in the fireball.

The explosion produces substances such as carbon dioxide, carbon monoxide, water vapor and nitrous oxide. These can all detected by the characteristic way each absorbs infrared light. Detailed analysis of the results provided the investigators with information about temperature and concentrations of these substances throughout the explosive event. They were also able to measure absorption and emission of infrared light from tiny solid particles (soot) created by the explosion.

The swept-ECQCL measurements provide a new way to study explosive detonations that could have other uses. In future studies, the investigators hope to extend the measurements to more wavelengths, faster scan rates, and higher resolutions.
The article, "Characterization of high-explosive detonations using broadband infrared external cavity quantum cascade laser absorption spectroscopy," is authored by Mark C. Phillips, Bruce E. Bernacki, Sivanandan S. Harilal, Brian E. Brumfield, Joel M. Schwallier and Nick G. Glumac. The article will appear in the Journal of Applied Physics on Sept. 3, 2019 (DOI: 10.1063/1.5107508). After that date, it can be accessed at


The Journal of Applied Physics is an influential international journal publishing significant new experimental and theoretical results in all areas of applied physics. See

American Institute of Physics

Related Molecules Articles from Brightsurf:

Finally, a way to see molecules 'wobble'
Researchers at the University of Rochester and the Fresnel Institute in France have found a way to visualize those molecules in even greater detail, showing their position and orientation in 3D, and even how they wobble and oscillate.

Water molecules are gold for nanocatalysis
Nanocatalysts made of gold nanoparticles dispersed on metal oxides are very promising for the industrial, selective oxidation of compounds, including alcohols, into valuable chemicals.

Water molecules dance in three
An international team of scientists has been able to shed new light on the properties of water at the molecular level.

How molecules self-assemble into superstructures
Most technical functional units are built bit by bit according to a well-designed construction plan.

Breaking down stubborn molecules
Seawater is more than just saltwater. The ocean is a veritable soup of chemicals.

Shaping the rings of molecules
Canadian chemists discover a natural process to control the shape of 'macrocycles,' molecules of large rings of atoms, for use in pharmaceuticals and electronics.

The mysterious movement of water molecules
Water is all around us and essential for life. Nevertheless, research into its behaviour at the atomic level -- above all how it interacts with surfaces -- is thin on the ground.

Spectroscopy: A fine sense for molecules
Scientists at the Laboratory for Attosecond Physics have developed a unique laser technology for the analysis of the molecular composition of biological samples.

Looking at the good vibes of molecules
Label-free dynamic detection of biomolecules is a major challenge in live-cell microscopy.

Colliding molecules and antiparticles
A study by Marcos Barp and Felipe Arretche from Brazil published in EPJ D shows a model of the interaction between positrons and simple molecules that is in good agreement with experimental results.

Read More: Molecules News and Molecules Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to