Doppler broadened NICE-OHMS beyond the triplet formalism: assessment of optimum modulation index
2014 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 31, no 7, 1499-1507 p.Article in journal (Refereed) Published
The dependence of Doppler broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) on the modulation index, beta, has been investigated experimentally on C2H2 and CO2, both in the absence and the presence of optical saturation. It is shown that the maximum signals are obtained for beta that produce more than one pair of sidebands: in the Doppler limit and for the prevailing conditions (unsaturated transition and the pertinent modulation frequency and Doppler widths) around 1 and 1.4 for the dispersion and absorption detection phases, respectively. The results verify predictions given in an accompanying work. It is also shown that there is no substantial broadening of the NICE-OHMS signal for beta < 1. The use of beta of unity has yielded a Db-NICE-OHMS detection sensitivity of 4.9 x 10(-12) cm(-1) Hz(-1/2), which is the lowest (best) value so far achieved for NICE-OHMS based on a tunable laser. The number of sidebands that needs to be included in fits of the line-shape function to obtain good accuracy has been assessed. It is concluded that it is enough to consider three pairs of sidebands whenever the systematic errors in a concentration assessment should be below 1% when beta < 2 are used and <1 parts per thousand for beta < 1.5.
Place, publisher, year, edition, pages
Optical Society of America, 2014. Vol. 31, no 7, 1499-1507 p.
Atom and Molecular Physics and Optics
IdentifiersURN: urn:nbn:se:umu:diva-91852DOI: 10.1364/JOSAB.31.001499ISI: 000338931700013OAI: oai:DiVA.org:umu-91852DiVA: diva2:740953
Ingår i Patrick Ehlers doktorsavhandling som delarbete nr XI med titeln: NICE-OHMS beyond the triplet formalism: assessment of the optimum modulation index.2014-08-262014-08-182015-10-22Bibliographically approved