Explosion is a complex process involving rapid changes in temperature, pressure and chemical concentration. In a paper published in the Journal of Applied Physics, scientists studied the explosion through a special type of infrared laser called swept wavelength external cavity quantum cascade laser (scanning ECQCL). This multi-functional instrument has a broad wavelength tuning range and can measure many chemical substances, even macromolecules, in explosive fireballs.
The ability to detect and monitor the violent changes of explosion can help scientists understand the explosion process and even control it. Measurements by solid temperature or pressure probes placed in explosive fireballs can provide specific physical data during explosion, but chemical changes that may occur during explosion cannot be measured. Although the final product of the explosion can be sampled, it can only be done after the explosion.
In this research work, we can detect the molecules in fireballs by monitoring their interaction with light, especially infrared light. This method of measurement is fast and safe. Lasers are needed because the fireballs are very turbulent and rich in strong absorbents.
By building new instruments in the laboratory, researchers can measure explosions faster, with higher resolution and longer duration than previously used infrared lasers.
Mark Phillips, co-author of the paper, said: "By scanning ECQCL, a new measurement method is realized by combining the best characteristics of high resolution tunable laser spectroscopy with broadband methods such as FTIR.
They studied four types of high-energy explosives, all of which were placed in a specially designed chamber to accommodate explosive fireballs. Laser beams from scanned ECQCL are guided to the chamber and the wavelength of the laser is rapidly changed. Lasers propagating through fireballs are recorded during each explosion to measure changes in the way infrared light is absorbed by molecules in fireballs.
The substances produced by the explosion include carbon dioxide, carbon monoxide, water vapor and nitrous oxide. All of these substances can be detected by their absorption of infrared light. Detailed analysis of the results provides researchers with information about the temperature and concentration of these substances in the whole explosion event. In addition, it can also measure the infrared absorption of small solid particles (smoke) produced by explosion.
Scanning ECQCL measurement method provides a new method for studying explosion method which may have other uses. In future research, researchers hope to extend the measurement range to more wavelength, faster scanning rate and higher resolution.
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