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Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry signals from optically saturated transitions under low pressure conditions
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
2008 (Engelska)Ingår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 25, nr 7, s. 1156-1165Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The influence of optical saturation on noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) signals from purely Doppler-broadened transitions is investigated experimentally. It is shown that the shape and the strength of the dispersion signal are virtually unaffected by optical saturation, whereas the strength of the absorption signal decreases as (1+G+-1)-1/2, where G+-1 is the degree of saturation induced by the sideband of the frequency modulated triplet, in agreement with theoretical predictions. This implies, first of all, that Doppler-broadened NICE-OHMS is affected less by optical saturation than other cavity enhanced techniques but also that it exhibits nonlinearities in the power and pressure dependence for all detection phases except pure dispersion. A methodology for assessments of the degree of saturation and the saturation power of a transition from Doppler-broadened NICE-OHMS signals is given. The implications of optical saturation for practical trace species detection by Doppler-broadened NICE-OHMS are discussed.

Ort, förlag, år, upplaga, sidor
2008. Vol. 25, nr 7, s. 1156-1165
Nyckelord [en]
spectroscopy heterodyne, spectroscopy modulation, absorption, trace species detection, cavity enhanced spectrometry
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
URN: urn:nbn:se:umu:diva-9811DOI: 10.1364/JOSAB.25.001156OAI: oai:DiVA.org:umu-9811DiVA, id: diva2:149482
Tillgänglig från: 2008-05-21 Skapad: 2008-05-21 Senast uppdaterad: 2018-06-09Bibliografiskt granskad
Ingår i avhandling
1. Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry
Öppna denna publikation i ny flik eller fönster >>Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry
2009 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Noise-immune cavity-enhanced optical heterodyne molecular spectro-metry (NICE-OHMS) is one of the most sensitive laser-based absorption techniques. The high sensitivity of NICE-OHMS is obtained by a unique combination of cavity enhancement (for increased interaction length with a sample) with frequency modulation spectrometry (for reduction of noise). Moreover, sub-Doppler detection is possible due to the presence of high intensity counter-propagating waves inside an external resonator, which provides an excellent spectral selectivity. The high sensitivity and selectivity make NICE-OHMS particularly suitable for trace gas detection. Despite this, the technique has so far not been often used for practical applications due to its technical complexity, originating primarily from the requirement of an active stabilization of the laser frequency to a cavity mode.

The main aim of the work presented in this thesis has been to develop a simpler and more robust NICE-OHMS instrumentation without compro-mising the high sensitivity and selectivity of the technique. A compact NICE-OHMS setup based on a fiber laser and a fiber-coupled electro-optic modulator has been constructed. The main advantage of the fiber laser is its narrow free-running linewidth, which significantly simplifies the frequency stabilization procedure. It has been demonstrated, using acetylene and carbon dioxide as pilot species, that the system is capable of detecting relative absorption down to 3 × 10-9 on a Doppler-broadened transition, and sub-Doppler optical phase shift down to 1.6 × 10-10, the latter corresponding to a detection limit of 1 × 10-12 atm of C2H2. Moreover, the potential of dual frequency modulation dispersion spectrometry (DFM-DS), an integral part of NICE-OHMS, for concentration measurements has been assessed.

This thesis contributes also to the theoretical description of Doppler-broadened and sub-Doppler NICE-OHMS signals, as well as DFM-DS signals. It has been shown that the concentration of an analyte can be deduced from a Doppler-broadened NICE-OHMS signal detected at an arbitrary and unknown detection phase, provided that a fit of the theoretical lineshape to the experimental data is performed. The influence of optical saturation on Doppler-broadened NICE-OHMS signals has been described theoretically and demonstrated experimentally. In particular, it has been shown that the Doppler-broadened dispersion signal is unaffected by optical saturation in the Doppler limit. An expression for the sub-Doppler optical phase shift, valid for high degrees of saturation, has been derived and verified experimentally up to degrees of saturation of 100.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå University, 2009. s. 145
Nyckelord
absorption spectrometry, frequency modulation, cavity enhancement, NICE-OHMS, Laser frequency stabilization, fiber laser, Fabry-Perot cavities, sub-Doppler spectroscopy, trace gas detection
Nationell ämneskategori
Fysik Atom- och molekylfysik och optik
Forskningsämne
fysik
Identifikatorer
urn:nbn:se:umu:diva-22269 (URN)978-91-7264-740-4 (ISBN)
Distributör:
Institutionen för fysik, 90187, Umeå
Disputation
2009-05-29, N430, Naturverarhuset Umeå universitet, Umeå, 09:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2009-05-08 Skapad: 2009-05-04 Senast uppdaterad: 2018-06-08Bibliografiskt granskad

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Förlagets fulltexthttp://josab.osa.org/DirectPDFAccess/0C3DCDC9-BDB9-137E-C541DA5626772E3C_91531.pdf?da=1&id=91531&seq=0&CFID=3807295&CFTOKEN=67222365

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Foltynowicz, AleksandraMa, WeiguangSchmidt, Florian M.Axner, Ove

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Atom- och molekylfysik och optik

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