3 research outputs found
Spectroscopie UV à Double Peigne de Fréquence (dual comb) en vue de l'étude de la molécule OH
The atmospheric gas phase evolution is of main concern for air quality and climate evolution, as indicated in the recent IPPC Report [1]. In this context, the radical OH has been recognized as one of the key molecule in the atmosphere, participating for instance to 90 % of the atmospheric methane loss. The radical OH interactions in the atmosphere remain not fully understood, as it is very challenging to measure. To improve the understanding of the role of OH in the atmosphere, there is a need for instruments that should be sensitive, accurate, and have a fast acquisition time in the timeframe of the OH lifetime (ms). We propose to extend the already existing dual comb spectroscopy (DCS) methodology instrument from the IR [2,3] to the near UV region to take advantage of the strong absorption cross-section of OH at 308 nm. Numerical and theoretical work [4] effectively assess the feasibility of the DCS method in the UV range. This study concludes that the TiSa Kerr lens mode-locked laser source appears to be the most adapted laser source to realize DCS in the UV. The advantages of the remote sensing DCS method are multiple: it is a fast acquisition rate with similar sensitivity than the existing spectroscopic methods, it is an in-situ method, free of sampling retrieval and free of atmospheric fluctuations. A homemade DCS laser source has been fully realized in the laboratory with an original geometry. It consists in a single ring cavity laser generating two pulses trains of 100 fs. This geometry is advantageous for DCS as it allows a common noise sharing (amplitude and phase). The total mode-locked emitted output power reaches 700 mW with 5.5 W pump power, which would provide enough power to probe atmospheric molecules with UV-DCS via third harmonic generation. The first tests of the DCS experiment using our homemade laser source have been realized on Fabry-Perot (FP) and O2 molecules. We retrieved accurately the free spectral range of the FP and obtained, with high accuracy, the ro-vibrational transitions position of O2 at 760 nm. We demonstrated that the here developed single cavity laser source provides high enough relative phase stability (at least 330 ms) between the two laser emissions. These first results represent an important milestone towards atmospheric trace gases remote sensing using UV-DCS. [1] IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press [2] Rieker, G. B., Giorgetta, F. R., Coddington, I., Swann, W. C., Sinclair, L. C., Cromer, C. L., ... & Newbury, N. R. (2013, November). Dual-comb spectroscopy of greenhouse gases over a 2-km outdoor path. In Optical Instrumentation for Energy and Environmental Applications (pp. ET2A-2). Optical Society of America. [3] Coburn, S., Alden, C. B., Wright, R., Cossel, K., Baumann, E., Truong, G. W., ... & Rieker, G. B. (2018). Regional trace-gas source attribution using a field-deployed dual frequency comb spectrometer. Optica, 5(4), 320-327. [4] Galtier, S., Pivard, C., & Rairoux, P. (2020). Towards DCS in the UV Spectral Range for Remote Sensing of Atmospheric Trace Gases. Remote Sensing, 12(20), 3444.L'évolution de la phase gazeuse atmosphérique est une préoccupation majeure pour la qualité de l'air et l'évolution du climat, comme indiqué dans le récent rapport du GIEC [1]. Dans ce contexte, le radical OH a été reconnu comme l'une des molécules clés de l'atmosphère, participant par exemple à 90 % de la réduction de méthane atmosphérique. Les interactions radicalaires OH dans l'atmosphère ne sont pas encore entièrement comprises car elles sont très difficiles à mesurer. Pour améliorer la compréhension du rôle de l'OH dans l'atmosphère, il existe un besoin d'instruments qui doivent être sensibles, précis et avoir un temps d'acquisition rapide dans la durée de vie de l'OH (ms). Nous proposons d'étendre la méthode de spectroscopie à double peigne de fréquence (DCS) déjà existant dans l'IR [2,3] à la région proche UV afin de tirer parti de la forte section efficace d'absorption de OH à 308 nm. Une étude numérique et théorique [4] a évalué efficacement la faisabilité de la méthode DCS dans le domaine UV. Cette étude conclut que la source laser Ti:sa à verrouillage de mode par effet Kerr semble être la source laser la plus adaptée pour réaliser le DCS dans l'UV. Les avantages de la méthode DCS pour la télédétection sont multiples : vitesse d'acquisition rapide avec une sensibilité similaire aux méthodes spectroscopiques existantes, c'est une méthode in-situ, sans prélèvement d'échantillons et indépendant des fluctuations atmosphériques. Une source laser DCS a été entièrement réalisée en laboratoire avec une géométrie originale. Il consiste en un laser à cavité en anneau unique générant deux trains d'impulsions de 100 fs. Cette géométrie est avantageuse pour la méthode DCS car elle permet un partage des bruits commun (amplitude et phase) aux deux impulsions.La puissance totale émise du laser à mode verrouillé atteint 700 mW avec une puissance de pompe de 5,5 W, ce qui fournit suffisamment de puissance pour sonder les molécules atmosphériques par UV-DCS via la génération de troisième harmonique. Les premiers tests de l'expérience DCS utilisant notre source laser ont été réalisés sur un étalon Fabry-Pérot (FP) et sur la molécule O2. Nous avons récupéré avec précision l’intervalle spectrale libre du FP et obtenu, avec une grande précision, la position des transitions ro-vibrationnelles de l'O2 à 760 nm. Nous avons démontré que la source laser à cavité unique développée ici offre une stabilité de phase relative suffisamment élevée (au moins 330 ms) entre les deux émissions laser. Ces premiers résultats représentent une étape importante vers la télédétection des gaz traces atmosphériques par UV-DCS. [1] IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press [2] Rieker, G. B., Giorgetta, F. R., Coddington, I., Swann, W. C., Sinclair, L. C., Cromer, C. L., ... & Newbury, N. R. (2013, November). Dual-comb spectroscopy of greenhouse gases over a 2-km outdoor path. In Optical Instrumentation for Energy and Environmental Applications (pp. ET2A-2). Optical Society of America. [3] Coburn, S., Alden, C. B., Wright, R., Cossel, K., Baumann, E., Truong, G. W., ... & Rieker, G. B. (2018). Regional trace-gas source attribution using a field-deployed dual frequency comb spectrometer. Optica, 5(4), 320-327. [4] Galtier, S., Pivard, C., & Rairoux, P. (2020). Towards DCS in the UV Spectral Range for Remote Sensing of Atmospheric Trace Gases. Remote Sensing, 12(20), 3444
Towards DCS in the UV Spectral Range for Remote Sensing of Atmospheric Trace Gases
The development of increasingly sensitive and robust instruments and new methodologies are essential to improve our understanding of the Earth’s climate and air pollution. In this context, Dual-Comb spectroscopy (DCS) has been successfully demonstrated as a remote laser-based instrument to probe infrared absorbing species such as greenhouse gases. We present here a study of the sensitivity of Dual-Comb spectroscopy to remotely monitor atmospheric gases focusing on molecules that absorb in the ultraviolet domain, where the most reactive molecules of the atmosphere (OH, HONO, BrO...) have their highest absorption cross-sections. We assess the achievable signal-to-noise ratio (SNR) and the corresponding minimum absorption sensitivity of DCS in the ultraviolet range. We propose a potential light source for remote sensing UV-DCS and discuss the degree of immunity of UV-DCS to atmospheric turbulences. We show that the characteristics of the currently available UV sources are compatible with the unambiguous identification of UV absorbing gases by UV-DCS
Feasibility of dual comb spectroscopy in the UV range using a free-running, bidirectional ring titanium sapphire laser
We show that our developed free-running, bidirectional ring Ti:Sa laser cavity meets the requirements for Dual Comb Spectroscopy in the UV range (UV-DCS). Two counter-propagative frequency combs with slightly different repetition rate are generated in such a cavity and we show quantitatively that this repetition rate difference can be explained by the self-steepening effect. Molecular absorption lines of the O2 A-band centered around 760~nm are measured with a 1,5 GHz spectral resolution, demonstrating that the mutual coherence of the two combs allows GHz-resolution DCS measurements. Moreover, we demonstrate that the generated output peak power allows for efficient second harmonic generation (SHG), in the scope of developing laboratory and open-path UV-DCS experiments