Voici les éléments 1 - 10 sur 15
- PublicationAccès libreComparison between Backscatter Lidar and Radiosonde Measurements of the Diurnal and Nocturnal Stratification in the Lower Troposphere(2007)
;Martucci, Giovanni ; ;Mitev, ValentinRichner, HansA collection of boundary layer heights has been derived from measurements performed by a ground-based backscatter lidar in Neuchâtel, Switzerland (47.000°N, 6.967°E, 485 m ASL). A dataset of 98 cases have been collected during 2 yr. From these data, 61 are noon and 37 are midnight cases. The following two different schemes were used to retrieve the mixed layer depth and the height of the residual layer from the measurements: the gradient and variance methods. The obtained values were compared with those derived from the potential temperature profiles as computed from radiosonde data. For nocturnal cases, the height of the first aerosol layer above the residual layer was also compared to the corresponding potential temperature value. Correlation coefficients between lidar and radiosonde in both convective and stable conditions are between 0.88 and 0.97.
- PublicationAccès libreAbsolute frequency referencing in the long wave infrared using a quantum cascade laser frequency combOptical frequency combs (OFCs) based on quantum cascade lasers (QCLs) have transformed mid-infrared spectroscopy. However, QCL-OFCs have not yet been exploited to provide a broadband absolute frequency reference. We demonstrate this possibility by performing comb-calibrated spectroscopy at 7.7 µm (1305 cm−1) using a QCL-OFC referenced to a molecular transition. We obtain 1.5·10−10 relative frequency stability (100-s integration time) and 3·10−9 relative frequency accuracy, comparable with state-of-the-art solutions relying on nonlinear frequency conversion. We show that QCL-OFCs can be locked with sub-Hz-level stability to a reference for hours, thus promising their use as metrological tools for the mid-infrared.
- PublicationAccès libreCoherently-averaged dual comb spectrometer at 7.7 µm with master and follower quantum cascade lasers(2021-6)
; ;Shehzad, Atif ;Terrasanta, Giulio ; ; ;Gianella, Michele ;Jouy, Pierre ;Kapsalidis, Filippos ;Shahmohammadi Mehran, Mehran ;Beck Matthias, Matthias ; ;Faist, Jérôme ;Emmenegger, Lukas ; ;Hugi, AndreasWe demonstrate coherent averaging of the multi-heterodyne beat signal between two quantum cascade laser frequency combs in a master-follower configuration. The two combs are mutually locked by acting on the drive current to control their relative offset frequency and by radio-frequency extraction and injection locking of their intermode beat signal to stabilize their mode spacing difference. By implementing an analog common-noise subtraction scheme, a reduction of the linewidth of all heterodyne beat notes by five orders of magnitude is achieved compared to the free-running lasers. We compare stabilization and post-processing corrections in terms of amplitude noise. While they give similar performances in terms of signal-to-noise ratio, real-time processing of the stabilized signal is less demanding in terms of computational power. Lastly, a proof-of-principle spectroscopic measurement was performed, showing the possibility to reduce the amount of data to be processed by three orders of magnitude, compared to the free-running system.
- PublicationMétadonnées seulementInterferometric measurements beyond the coherence length of the laser sourceInterferometric measurements beyond the coherence length of the laser are investigated theoretically and experimentally in this paper. Thanks to a high-bandwidth detection, high-speed digitizers and a fast digital signal processing, we have demonstrated that the limit of the coherence length can be overcome. Theoretically, the maximal measurable displacement is infinite provided that the sampling rate is sufficiently short to prevent any phase unwrapping error. We could verify experimentally this concept using a miniature interferometer prototype, based on a frequency stabilized vertical cavity surface emitting laser. Displacement measurements at optical path differences up to 36 m could be realized with a relative stability better than 0.1 ppm, although the coherence length estimated from the linewidth and frequency noise measurements do not exceed 6.6 m.
- PublicationAccès libreUnprecedented evidence for deep convection hydrating the tropical stratosphere(2008)
;Corti, T. ;Luo, B. P. ;de Reus, M. ;Brunner, D. ;Cairo, F. ;Mahoney, M. J. ;Martucci, G. ; ;Mitev, Valentin ;dos Santos, F. H. ;Schiller, C. ;Shur, G. ;Sitnikov, N. M. ;Spelten, N. ;Vössing, H. J. ;Borrmann, S.Peter, T.We report on in situ and remote sensing measurements of ice particles in the tropical stratosphere found during the Geophysica campaigns TROCCINOX and SCOUT-O3. We show that the deep convective systems penetrated the stratosphere and deposited ice particles at altitudes reaching 420 K potential temperature. These convective events had a hydrating effect on the lower tropical stratosphere due to evaporation of the ice particles. In contrast, there were no signs of convectively induced dehydration in the stratosphere.
- PublicationAccès libreDiode laser frequency stabilisation for water vapour differential absorption sensingWe describe a low-power continuous-wave laser system for water-vapour sensing applications in the 935-nm region. The system is based on extended-cavity diode lasers and distributed-feedback lasers and delivers four single-mode frequency-stabilised optical signals. Three lasers are locked to three water-vapour absorption lines of different strengths, whereas the fourth lies outside any absorption line. On-line stabilisation is performed by wavelength-modulation spectroscopy using compact water-vapour reference cells. An offset-locking technique implemented around an electrical filter is applied for the stabilisation of the off-line slave laser to an on-line master laser at a frequency detuning of 18.8 GHz. Stabilities in the order of 15 MHz over one day were observed for the strongest lines, at the detection limit of the measurement instrumentation. The developed techniques and schemes can be applied to other wavelength ranges and molecular species. Differential absorption lidar instrumentation can in particular benefit from such a system when the stabilised lasers serve as injection seeders to pulsed power oscillators.
- PublicationAccès libreEvaluation of the frequency stability of a VCSEL locked to a micro-fabricated Rubidium vapour cellWe present our evaluation of a compact laser system made of a 795 nm VCSEL locked to the Rubidium absorption line of a micro-fabricated absorption cell. The spectrum of the VCSEL was characterised, including its RIN, FM noise and line-width. We optimised the signal-to-noise ratio and determined the frequency shifts versus the cell temperature and the incident optical power. The frequency stability of the laser (Allan deviation) was measured using a high-resolution wavemeter and an ECDL-based reference. Our results show that a fractional instability of ≥ 10-9 may be reached at any timescale between 1 and 100'000 s. The MEMS cell was realised by dispensing the Rubidium in a glass-Silicon preform which was then, sealed by anodic bonding. The overall thickness of the reference cell is 1.5 mm. No buffer gas was added. The potential applications of this compact and low-consumption system range from optical interferometers to basic laser spectroscopy. It is particularly attractive for mobile and space instruments where stable and accurate wavelength references are needed.
- PublicationAccès libreLaser offset-frequency locking up to 20 GHz using a low-frequency electrical filter techniqueA simple, easy-to-implement, and robust technique is reported to offset lock two semiconductor lasers with a frequency difference easily adjustable up to a couple of tens of gigahertz (10 and 19 GHz experimentally demonstrated). The proposed scheme essentially makes use of low-frequency control electronics and may be implemented with any type of single mode semiconductor laser, without any requirement for the laser linewidth. The technique is shown to be very similar to the wavelength modulation spectroscopy method commonly used for laser stabilization onto molecular absorption lines, as demonstrated by experimental results obtained using 935 nm laser diodes.
- PublicationAccès libreCompact rubidium-stabilized multi-frequency reference source in the 1.55-μm regionCombining light modulation and frequency conversion techniques, a compact and simple frequency-stabilized optical frequency comb spanning over 45 nm in the 1.56-μm wavelength region is demonstrated. It benefits from the high-frequency stability achievable from rubidium atomic transitions at 780 nm probed in a saturation absorption scheme, which is transferred to the 1.56-μm spectral region via a second-harmonic generation process. The optical frequency comb is generated by an electro-optic modulator enclosed in a Fabry–Perot cavity that is injected by the fundamental frequency stabilized laser. Frequency stability better than 2 kHz has been demonstrated on time scales between 1000 s and 2 days both at 1560 nm, twice the rubidium wavelength, and for a comb line at 1557 nm.
- PublicationMétadonnées seulementRb-stabilized laser at 1572 nm for CO2 monitoringWe have developed a compact rubidium-stabilized laser system to serve as optical frequency reference in the 1.55-m wavelength region, in particular for CO2 monitoring at 1572 nm. The light of a fiber-pigtailed distributed feedback (DFB) laser emitting at 1560 nm is frequency-doubled and locked to a sub-Doppler rubidium transition at 780 nm using a 2-cm long vapor glass cell. Part of the DFB laser light is modulated with an electro-optical modula-tor enclosed in a Fabry-Perot cavity, generating an optical frequency comb with spectral cover-age extending from 1540 nm to 1580 nm. A second slave DFB laser emitting at 1572 nm and offset-locked to one line of the frequency comb shows a relative frequency stability of 1·10-11at 1 s averaging time and <4·10-12 from 1 hour up to 3 days.