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The design of sensitive and species-selective laser diagnostics critically depends on precise and accurate knowledge of an extensive list of molecules, including not only the target species but also all possible interfering species. The previous experimental and theoretical initiatives that provide information on intensity/opacity are usually limited in temperature, and therefore can be unreliable in wavelength selection and sensor optimization for applications at elevated temperatures. This noticeable lack of knowledge is a particular challenge that hinders our understanding of spectroscopy physics and undermines the performance of many absorption diagnostics.
I devoted half of my PhD career to developing an efficient approach to extend the study of broadband spectroscopy to temperatures previously impossible due to window material properties and species thermal instabilities. Using rapid-tuning broad-scan lasers in conjunction with shock tube facilities, the methodology navigates both issues and can acquire information of full-band (>100 cm-1, 100 times wider than conventional diode lasers) absorption within the test time of only a few milliseconds.
System integration
Components: shock tube, lasers, optics, detectors, spectral analyzer, DAQ, triggering circuits (soldered in-house) and LabVIEW interface
Automation in data analysis
I wrote original MATLAB codes to address the well-know "mode-hop" issue of this type of laser (with smart algorithms for lasing pattern recognition), and to automate the processing of massive data set of >100MB to critical results of <20KB.
Methodology validation
I rigorously tested the methodology and carefully quantified the measurement uncertainty. Below is a figure showing the good agreement of measured propene room-temperature absorption with the previous best knowledge in the literature.
Scientific contribution
This is the very first demonstration of the methodology in shock-heated gas and also the world-first broadband spectra at a temperature of 1000 K (previous work are limited below 500 K).
Data serve as reference for designing laser-based sensors
Data serve as validation for empirical or theoretical spectral databases (in this specific example, an ab initio model outperforms the famous HITRAN model)
ShockGas-IR: an empirical database for high-temperature mid-infrared absorption information
I and my collaborators have extended the study to a selected list of important species in combustion and planetary science, and constructed the Stanford ShockGas-IR database that comprises >50 high-temperature broadband spectra for >10 molecular species. These high-fidelity data are unique because of their test temperatures (600 - 1600 K) and wide spectral range (>100 cm-1).
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