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- 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.
- 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.
- PublicationMétadonnées seulementDFB-ridge laser diodes at 894 nm for Cesium atomic clocksTime and frequency applications are in need of high accuracy and high stability clocks. Optically pumped compact industrial Cesium atomic clocks are a promising approach that could satisfy these demands. However, the stability of these clocks relies, among others, on the performances of the laser diodes that are used. This issue has led the III-V Lab to commit to the European Euripides-LAMA project that aims to provide competitive compact optical Cesium clocks for ground applications. This work will provide key experience for further space technology qualification. III-V Lab is in charge of the design, fabrication and reliability of Distributed-Feedback diodes (DFB) at 894 nm (D1 line of Cesium) and 852 nm (D2 line). LTF-Unine is in charge of their spectral characterisation. The use of D1 line for pumping will provide simplified clock architecture compared to the D2 line pumping thanks to simpler atomic transitions and a larger spectral separation between lines in the 894 nm case. Also, D1 line pumping overcomes the issue of unpumped “idle states” that occur with D2 line. The modules should provide narrow linewidth (<1 MHz), very good reliability in time and, crucially, be less sensitive to optical feedback. The development of the 894 nm wavelength is grounded on III-V Lab results for 852 nm DFB. We show here results from Al-free active region with InGaAsP quantum well Ridge DFB lasers. We obtain the D1 Cs line (894.4 nm) at 67°C and 165 mA (optical power of 40 mW) with a high side mode suppression ratio. The wavelength evolution with temperature and current are respectively 0.06 nm/K and 0.003 nm/mA. The laser linewidth is less than 1 MHz. The Relative Intensity Noise (RIN) and the frequency noise are respectively less than 10-12 Hz-1 @ f ≥ 10 Hz and 109 Hz2/Hz @ f ≥ 10 Hz.
- PublicationMétadonnées seulementDevelopment of tuneable, narrow-band, and frequency stabilised laser heads in Observatoire Cantonal de NeuchâtelWe describe our investigations on tuneable, narrowband and frequency stabilised laser heads. The work is motivated by the potentials of highly stable and narrowband laser light sources for a variety of technical and scientific applications and in particular for atomic clocks and high resolution space instruments.