Plasma applications heavily depend on atomic oxygen densities, but knowing those densities requires precise and accurate diagnostic techniques. Researchers from Germany have developed the first implementation of THz QCLs for high-resolution absorption spectroscopy on plasmas, detecting absolute densities of ground state atomic oxygen at the fine structure transition at 4.75 THz. Validated with three transitions of ammonia close to this atomic oxygen line, this technique and measurement accuracy is within 5% and the detection limit is 2×1013 cm-3. This shows promising results for applications in plasma research and proves the diagnostic capabilities of THz absorption spectroscopy with QCLs.
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