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Wavelength modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy signal line shapes in the Doppler limit
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. (Laser Physics Group)
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
2009 (Engelska)Ingår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 26, nr 7, s. 1384-1394Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A thorough analysis of the shape and strength of Doppler-broadened wavelength modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy signals is presented and their dependence on modulation frequency, modulation amplitude and detection phase is investigated in detail. The conditions that maximize the on-resonance signal are identified. The analysis is based on the standard frequency modulation spectroscopy formalism and the Fourier description of wavelength modulation spectroscopy and verified by fits to experimental signals from C2H2 and CO2 measured at 1531 nm. In addition, the line strengths of two CO2 transitions in the v2→3v1+v2+v3 hot band [Pe(7) and Pe(9)] were found to differ by ~20% from those given in the HITRAN database.

Ort, förlag, år, upplaga, sidor
2009. Vol. 26, nr 7, s. 1384-1394
Nyckelord [en]
heterodyne spectroscopy, modulation spectroscopy, absorption, line shapes and shifts, cavity enhanced spectroscopy
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
URN: urn:nbn:se:umu:diva-22312DOI: 10.1364/JOSAB.26.001384ISI: 000268542200018OAI: oai:DiVA.org:umu-22312DiVA, id: diva2:214402
Tillgänglig från: 2009-05-05 Skapad: 2009-05-05 Senast uppdaterad: 2018-06-08Bibliografiskt 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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Foltynowicz, AleksandraMa, WeiguangSchmidt, Florian MAxner, Ove

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Journal of the Optical Society of America. B, Optical physics
Atom- och molekylfysik och optik

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