Dispersion spectroscopy and intra-cavity QEPAS for isotope analysis

WP3: Industrial Process Monitoring

Recruiting Host

Technische Universität Wien

Vienna, Austria


Prof. Dr. Bernhard Lendl


Munster Technological University

Cork, Ireland


Dr. Liam O’Faolain

This project will build on the results obtained when developing a QCL-based high-finesse spectrometer for integration with QEPAS sensors as carried out previously. It will compare the achieved analytical figures of merit with those from an experimental set-up to be built for dispersion spectroscopy. For injecting the laser in a high-finesse cavity and for generating the three tone signal required in dispersion spectroscopy, the laser needs to be stabilized and/or accurately modulated.

One of the main challenges for optical techniques is the detection of extremely low-abundance molecules. Among them, isotopes concentration detection, like for example 14N15N16O vs. 15N14N16O or 13CO2 / 13CH4, are of high relevance. For decades, high-sensitivity radiocarbon detection has been a prerogative of accelerator mass spectrometry (AMS), thus confined to remote “large facilities”, and with actual data analysis rates restricted by high costs and slow turnaround times. In this PhD project, we propose innovative solutions for all-optical isotopes detection. The proposed solutions are based on dispersion spectroscopy (this ESR project) as well as quartz-enhanced photoacoustic spectroscopy (QEPAS) which has already been dealt with in other ESR projects. We will develop an innovative spectroscopic approach combining the advantages of ultra-rapid current modulation of the semiconductor laser capable of measuring laughing gas (N2O) as well as carbon monoxide (CO) with miniaturized gas cells employing a multiple-folded optical path. Basic signal processing will start at TU Wien based on recent results in 2f wavelength modulation spectroscopy. Upon increasing the modulation speed from the tens of kHz to the single digit GHz frequencies the transition to dispersion spectroscopy will be made. Advanced developments in electronics and signal processing using FPGA programming will be carried out at MTU.