Quartz Control
Researchers get photoacoustic spectroscopy under control for rapid trace gas analysis
| News
Credit: Florian Sterl, Sterltech Optics GmbH
A new approach to trace gas detection, known as coherently controlled quartz-enhanced photoacoustic spectroscopy (COCO-QEPAS), allows for the identification of gas concentrations in seconds – overcoming limitations of traditional photoacoustic methods. The technique, developed by researchers at the University of Stuttgart, Germany, could become a fast and more versatile tool for environmental monitoring, medical diagnostics, and industrial safety applications.
The system combines a rapidly tunable laser and a “quartz tuning fork” to identify gases based on their unique light absorption patterns or "fingerprints." However, the high quality (Q)-factor of the tuning fork, while enhancing sensitivity, traditionally limits acquisition speed by causing lingering vibrations that blur spectral features during fast scans.
To address this, the team introduced a coherent control strategy. “When we change wavelengths to obtain the fingerprint of the molecule, the fork is still moving. To measure the next feature, we must somehow stop the movement,” explained Simon Angstenberger, the study’s lead author, in a press release. By timing laser pulses to arrive at specific points in the fork’s oscillation cycle, the system damps vibrations, enabling rapid successive measurements without compromising spectral clarity.
The researchers demonstrated the method by analyzing a methane mixture with 100 parts per million concentration. Using a laser developed by Stuttgart Instruments and a QEPAS gas cell, they acquired a complete methane spectrum across a wavelength range of 3050–3450 nanometers in just three seconds, a process that would typically take about 30 minutes.
“Adding coherent control to QEPAS enables ultra-fast identification of gases using their vibrational and rotational fingerprints,” Angstenberger said. “Unlike traditional setups limited to specific gases or single absorption peaks, we can achieve real-time monitoring with a broad laser tuning range of 1.3 to 18 µm, making it capable of detecting virtually any trace gas.”
The system has wide-ranging applications, from monitoring greenhouse gases to detecting toxic or flammable gases in industrial settings. It could also play a role in early disease detection through breath analysis.
Future research will focus on testing the system’s speed and sensitivity limits and expanding its capability to detect multiple gases simultaneously.
