Thèse Année : 2017

Development and application of a diode laser spectrometer for the measurement of isotope anomalies in carbon dioxide

Développement et applications d’un spectromètre laser dédié à la mesure des anomalies isotopiques du dioxyde de carbone

Résumé

High-precision molecular absorption spectroscopy has become a widely used tool in physics and metrology. More recently, such techniques have gained some favor in the earth sciences and industrial monitoring, mostly for their compactness and robustness. The determination of isotopic ratios of di fferent isotopic systems is nowadays possible with commercially available laser spectrometers. However, in particular for CO2, the full potential of such techniques for highest precision measurements has yet to be exploited. In this thesis, we present a new spectrometer based on optical feedback frequency locking of a distributed feedback laser (DFB) to a highly stable V-shaped reference cell. In such way, we obtain a near infra-red source reaching sub-kHz frequency resolution with a drift of 30 Hz/s. This ultra-narrow, ultra-stable laser source was then combined with a high-stability, high- finesse ring-down cell, using a robust dither lock scheme. We demonstrated a single-spectrum sensitivity of 1.2 x 10-12 cm-1, obtained in 30 seconds, and reported, for a narrow scan, a record-setting minimum detection level 3.8 x 10-14 cm-1, after less than 10 hours of measurement. We applied this instrument to the measurement of isotopic ratios in CO2 and demonstrated the feasibility of direct measurements of 17O in CO2. 17O is a super-ratio which requires precise measurements of three isotopologues, o ffering information on the hydrological environment of the past, if measured from carbonate rocks. The instrument yielded a precision of 10 ppm in a record-setting measurement time of 10 minutes, demonstrating that laser spectrometers now perform on the same level as state-of-the-art isotopic ratio mass spectrometers currently used in geoscientifi c studies. We also demonstrated the rst laser based measurements of the ratio 16O13C18O/13C16O2 ("clumped isotopes"), demonstrating a precision of 20 ppm with a strong potential to go further. The instrument shows the potential to measure all geoscienti fically relevant isotopologue ratios in CO2 in one single measurement.Furthermore, we applied the instrument to Doppler-free saturated absorption spectroscopy. We determined the transition frequencies of the 3001200001 band of 16O13C16O in natural abundance with kHz accuracy by referencing the laser source to a GPS-referenced optical frequency comb. Using combination di fferences, we were able to redetermine the B,D and H constant of the upper and lower state, providingevidence for di erences between our experimental data and literature. Moreover, we investigated the S(2) transition of D2. The zero-pressure transition frequency was determined with a record-setting precision of 32 kHz, meaning an accuracy of 0.17 ppb. The impact of line pro le choices on the retrieval of line specific c parameters has been investigated. The instrumentation which was built during this thesis ful lfils two major tasks: First, we have proven the capability of measuring 17O in CO2 with outstanding precision in record time. Moreover, we demonstrated a successful proof of concept for clumped isotope measurements. While a thorough investigation of memory effects and external reproducibility has yet to be done, it shows the great potential of this technique for use in the geosciences. Secondly, the instrument is a valuable tool for spectroscopy, exhibiting extremely high sensitivity and thus allowing the very precise determination of line-shape parameters and the validation of the most advanced line pro les. Moreover, com breferencing allows for precise and accurate determination of transition frequencies and pressure induced shifts.

High-precision molecular absorption spectroscopy has become a widely used tool in physics and metrology. More recently, such techniques have gained some favor in the earth sciences and industrial monitoring, mostly for their compactness and robustness. The determination of isotopic ratios of di fferent isotopic systems is nowadays possible with commercially available laser spectrometers. However, in particular for CO2, the full potential of such techniques for highest precision measurements has yet to be exploited. In this thesis, we present a new spectrometer based on optical feedback frequency locking of a distributed feedback laser (DFB) to a highly stable V-shaped reference cell. In such way, we obtain a near infra-red source reaching sub-kHz frequency resolution with a drift of 30 Hz/s. This ultra-narrow, ultra-stable laser source was then combined with a high-stability, high- finesse ring-down cell, using a robust dither lock scheme. We demonstrated a single-spectrum sensitivity of 1.2 x 10-12 cm-1, obtained in 30 seconds, and reported, for a narrow scan, a record-setting minimum detection level 3.8 x 10-14 cm-1, after less than 10 hours of measurement. We applied this instrument to the measurement of isotopic ratios in CO2 and demonstrated the feasibility of direct measurements of 17O in CO2. 17O is a super-ratio which requires precise measurements of three isotopologues, o ffering information on the hydrological environment of the past, if measured from carbonate rocks. The instrument yielded a precision of 10 ppm in a record-setting measurement time of 10 minutes, demonstrating that laser spectrometers now perform on the same level as state-of-the-art isotopic ratio mass spectrometers currently used in geoscientifi c studies. We also demonstrated the rst laser based measurements of the ratio 16O13C18O/13C16O2 ("clumped isotopes"), demonstrating a precision of 20 ppm with a strong potential to go further. The instrument shows the potential to measure all geoscienti fically relevant isotopologue ratios in CO2 in one single measurement.Furthermore, we applied the instrument to Doppler-free saturated absorption spectroscopy. We determined the transition frequencies of the 3001200001 band of 16O13C16O in natural abundance with kHz accuracy by referencing the laser source to a GPS-referenced optical frequency comb. Using combination di fferences, we were able to redetermine the B,D and H constant of the upper and lower state, providingevidence for di erences between our experimental data and literature. Moreover, we investigated the S(2) transition of D2. The zero-pressure transition frequency was determined with a record-setting precision of 32 kHz, meaning an accuracy of 0.17 ppb. The impact of line pro le choices on the retrieval of line specific c parameters has been investigated. The instrumentation which was built during this thesis ful lfils two major tasks: First, we have proven the capability of measuring 17O in CO2 with outstanding precision in record time. Moreover, we demonstrated a successful proof of concept for clumped isotope measurements. While a thorough investigation of memory effects and external reproducibility has yet to be done, it shows the great potential of this technique for use in the geosciences. Secondly, the instrument is a valuable tool for spectroscopy, exhibiting extremely high sensitivity and thus allowing the very precise determination of line-shape parameters and the validation of the most advanced line pro les. Moreover, com breferencing allows for precise and accurate determination of transition frequencies and pressure induced shifts.

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tel-02480995 , version 1 (17-02-2020)

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  • HAL Id : tel-02480995 , version 1

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Tim Stoltmann. Development and application of a diode laser spectrometer for the measurement of isotope anomalies in carbon dioxide. Optics [physics.optics]. Université Grenoble Alpes, 2017. English. ⟨NNT : ⟩. ⟨tel-02480995⟩

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