Characterization of Cs vapor cell coated with octadecyltrichlorosilane using coherent population trapping spectroscopy

We report the realization and characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The dual-structure of the resonance lineshape, with presence of a narrow structure line at the top of a Doppler-broadened structure, is clearly observed. The linewidth of the narrow resonance is compared to the linewidth of an evacuated Cs cell and of a buffer gas Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42 $\pm$ 0.03) eV, leading to a clock frequency shift rate of $2.7\times10^{-9}/$K in fractional unit. A hyperfine population lifetime, $T_1$, and a microwave coherence lifetime, $T_2$, of 1.6 and 0.5 ms are reported, corresponding to about 37 and 12 useful bounces, respectively. Atomic-motion induced Ramsey narrowing of dark resonances is observed in Cs-OTS cells by reducing the optical beam diameter. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme. Potential applications of the Cs-OTS cell to the development of a vapor cell atomic clock are discussed.Comment: 33 pages, 13 figure

Laser light routing in an elongated micromachined vapor cell with diffraction gratings for atomic clock applications

International audienceThis paper reports on an original architecture of microfabricated alkali vapor cell designed for miniature atomic clocks. The cell combines diffraction gratings with anisotropically etched single-crystalline silicon sidewalls to route a normally-incident beam in a cavity oriented along the substrate plane. Gratings have been specifically designed to diffract circularly polarized light in the first order, the latter having an angle of diffraction matching the (111) sidewalls orientation. Then, the length of the cavity where light interacts with alkali atoms can be extended. We demonstrate that a longer cell allows to reduce the beam diameter, while preserving the clock performances. As the cavity depth and the beam diameter are reduced, collimation can be performed in a tighter space. This solution relaxes the constraints on the device packaging and is suitable for wafer-level assembly. Several cells have been fabricated and characterized in a clock setup using coherent population trapping spectroscopy. The measured signals exhibit null power linewidths down to 2.23 kHz and high transmission contrasts up to 17%. A high contrast-to-linewidth ratio is found at a linewidth of 4.17 kHz and a contrast of 5.2% in a 7-mm-long cell despite a beam diameter reduced to 600 μm

Guidelines for developing optical clocks with 10−1810^{-18} fractional frequency uncertainty

There has been tremendous progress in the performance of optical frequency standards since the first proposals to carry out precision spectroscopy on trapped, single ions in the 1970s. The estimated fractional frequency uncertainty of today's leading optical standards is currently in the $10^{-18}$ range, approximately two orders of magnitude better than that of the best caesium primary frequency standards. This exceptional accuracy and stability is resulting in a growing number of research groups developing optical clocks. While good review papers covering the topic already exist, more practical guidelines are needed as a complement. The purpose of this document is therefore to provide technical guidance for researchers starting in the field of optical clocks. The target audience includes national metrology institutes (NMIs) wanting to set up optical clocks (or subsystems thereof) and PhD students and postdocs entering the field. Another potential audience is academic groups with experience in atomic physics and atom or ion trapping, but with less experience of time and frequency metrology and optical clock requirements. These guidelines have arisen from the scope of the EMPIR project "Optical clocks with $1 imes 10^{-18}$ uncertainty" (OC18). Therefore, the examples are from European laboratories even though similar work is carried out all over the world. The goal of OC18 was to push the development of optical clocks by improving each of the necessary subsystems: ultrastable lasers, neutral-atom and single-ion traps, and interrogation techniques. This document shares the knowledge acquired by the OC18 project consortium and gives practical guidance on each of these aspects

Guidelines for developing optical clocks with 10-18 fractional frequency uncertainty

There has been tremendous progress in the performance of optical frequency standards since the first proposals to carry out precision spectroscopy on trapped, single ions in the 1970s. The estimated fractional frequency uncertainty of today's leading optical standards is currently in the 10−18 range, approximately two orders of magnitude better than that of the best caesium primary frequency standards. This exceptional accuracy and stability is resulting in a growing number of research groups developing optical clocks. While good review papers covering the topic already exist, more practical guidelines are needed as a complement. The purpose of this document is therefore to provide technical guidance for researchers starting in the field of optical clocks. The target audience includes national metrology institutes (NMIs) wanting to set up optical clocks (or subsystems thereof) and PhD students and postdocs entering the field. Another potential audience is academic groups with experience in atomic physics and atom or ion trapping, but with less experience of time and frequency metrology and optical clock requirements. These guidelines have arisen from the scope of the EMPIR project "Optical clocks with 1×10−18 uncertainty" (OC18). Therefore, the examples are from European laboratories even though similar work is carried out all over the world. The goal of OC18 was to push the development of optical clocks by improving each of the necessary subsystems: ultrastable lasers, neutral-atom and single-ion traps, and interrogation techniques. This document shares the knowledge acquired by the OC18 project consortium and gives practical guidance on each of these aspects.EU/Horizon2020/EMPIR/E

Pooled analysis of WHO Surgical Safety Checklist use and mortality after emergency laparotomy

Background The World Health Organization (WHO) Surgical Safety Checklist has fostered safe practice for 10 years, yet its place in emergency surgery has not been assessed on a global scale. The aim of this study was to evaluate reported checklist use in emergency settings and examine the relationship with perioperative mortality in patients who had emergency laparotomy. Methods In two multinational cohort studies, adults undergoing emergency laparotomy were compared with those having elective gastrointestinal surgery. Relationships between reported checklist use and mortality were determined using multivariable logistic regression and bootstrapped simulation. Results Of 12 296 patients included from 76 countries, 4843 underwent emergency laparotomy. After adjusting for patient and disease factors, checklist use before emergency laparotomy was more common in countries with a high Human Development Index (HDI) (2455 of 2741, 89.6 per cent) compared with that in countries with a middle (753 of 1242, 60.6 per cent; odds ratio (OR) 0.17, 95 per cent c.i. 0.14 to 0.21, P <0001) or low (363 of 860, 422 per cent; OR 008, 007 to 010, P <0.001) HDI. Checklist use was less common in elective surgery than for emergency laparotomy in high-HDI countries (risk difference -94 (95 per cent c.i. -11.9 to -6.9) per cent; P <0001), but the relationship was reversed in low-HDI countries (+121 (+7.0 to +173) per cent; P <0001). In multivariable models, checklist use was associated with a lower 30-day perioperative mortality (OR 0.60, 0.50 to 073; P <0.001). The greatest absolute benefit was seen for emergency surgery in low- and middle-HDI countries. Conclusion Checklist use in emergency laparotomy was associated with a significantly lower perioperative mortality rate. Checklist use in low-HDI countries was half that in high-HDI countries.Peer reviewe

Global variation in anastomosis and end colostomy formation following left-sided colorectal resection

Background End colostomy rates following colorectal resection vary across institutions in high-income settings, being influenced by patient, disease, surgeon and system factors. This study aimed to assess global variation in end colostomy rates after left-sided colorectal resection. Methods This study comprised an analysis of GlobalSurg-1 and -2 international, prospective, observational cohort studies (2014, 2016), including consecutive adult patients undergoing elective or emergency left-sided colorectal resection within discrete 2-week windows. Countries were grouped into high-, middle- and low-income tertiles according to the United Nations Human Development Index (HDI). Factors associated with colostomy formation versus primary anastomosis were explored using a multilevel, multivariable logistic regression model. Results In total, 1635 patients from 242 hospitals in 57 countries undergoing left-sided colorectal resection were included: 113 (6·9 per cent) from low-HDI, 254 (15·5 per cent) from middle-HDI and 1268 (77·6 per cent) from high-HDI countries. There was a higher proportion of patients with perforated disease (57·5, 40·9 and 35·4 per cent; P < 0·001) and subsequent use of end colostomy (52·2, 24·8 and 18·9 per cent; P < 0·001) in low- compared with middle- and high-HDI settings. The association with colostomy use in low-HDI settings persisted (odds ratio (OR) 3·20, 95 per cent c.i. 1·35 to 7·57; P = 0·008) after risk adjustment for malignant disease (OR 2·34, 1·65 to 3·32; P < 0·001), emergency surgery (OR 4·08, 2·73 to 6·10; P < 0·001), time to operation at least 48 h (OR 1·99, 1·28 to 3·09; P = 0·002) and disease perforation (OR 4·00, 2·81 to 5·69; P < 0·001). Conclusion Global differences existed in the proportion of patients receiving end stomas after left-sided colorectal resection based on income, which went beyond case mix alone

Développement et caractérisation métrologique d'une horloge atomique à cellule de Cs à piégeage cohérent de population de haute performance

This thesis work, performed in the frame of the MClocks European project (http://www.inrim.it/mclocks), reports the development and metrological characterization of a high-performance Cs vapor cell atomic clock based on coherent population trapping (CPT). The clock uses an optimized CPT pumping scheme, named push-pull optical pumping (PPOP), allowing the detection of high-contrast CPT resonances on the 0-0 magnetic-field insensitive clock transition. A detailed characterization of key components of the clock is reported. The clock was operated in the continuous-wave (CW) regime and in a Ramsey-like pulsed regime. In both regimes, the clock demonstrates a short-term fractional frequency stability at the level of 2 10−13 τ−1/2 up to 100 s averaging time, mainly limited by laser power effects. This CPT clock, ranking among the best microwave vapor cell atomic frequency standards, could find applications in telecommunication, instrumentation, defense or satellite-based navigation systems.This thesis reports also a novel laser frequency stabilization technique using dual-frequency sub-Doppler spectroscopy in a vapor cell. The clock ”platform” has also been used to perform using CPT spectroscopy the characterization of a Cs vapor cell coated with octadecyltrichlorosilane (OTS) or original buffer-gas filled Cs vapor micro-fabricated cells developed in FEMTO-ST for CPT-based miniature atomic clocks.Ce travail de thèse, effectué dans le cadre du projet européen MClocks (http://www.inrim.it/mclocks), reporte le développement et la caractérisation métrologique d’une horloge atomique à cellule de césium de haute performance basée sur le phénomène de piégeage cohérent de population (CPT). Cette horloge exploite un schéma de pompage CPT optimisé nommé push-pull optical pumping (PPOP), permettant la détection de résonances CPT à fort contraste sur la transition d’horloge 0-0. Une caractérisation détaillée des différents éléments de l’horloge est reportée. L’horloge fut exploitée en mode continu (CW) et en mode impulsionnel de type Ramsey. Dans les deux modes de fonctionnement, l’horloge démontre une stabilité relative de fréquence de l’ordre de 2 10−13 τ−1/2 jusque 100 s d’intégration, principalement limitée par des effets de puissance laser. Cette horloge atomique, parmi les meilleures horloges à cellule développées à travers le monde, pourrait trouver des applications pour les systèmes de télécommunications, d’instrumentation, de défense ou navigation par satellite.Cette thèse reporte aussi une technique originale de stabilisation de fréquence laser par spectroscopie sub-Dopplerbi-fréquence en cellule. La plateforme constituée par l’horloge a été utilisée pour mener des tests de physique plus amont incluant la caractérisation par spectroscopie CPT d’une cellule de césium avec un revêtement anti-relaxant OTS (octadecyltrichlorosilane) ou la caractérisation de microcellules à vapeur de césium avec gaz tampon développées à FEMTO-ST pour des horloges atomiques miniatures

A high-performance CPT-based Cs vapor cell atomic clock using pushpull optical pumping

International audienceMicrowave vapor cell atomic clocks are exciting candidates for numerous timekeeping applications because they combine compactness, a modest power consumption and excellent fractional frequency stability at the level of a few 10-13 t-1/2 [1,2,3]. In the frame of the MClocks project funded by EURAMET, we report on the development of a Cs vapor cell atomic clock based on coherent population trapping (CPT)

A coherent population trapping Cs vapor cell atomic clock based on push-pull optical pumping

International audienceThis article reports on the characterization of a compact coherent-population-trapping (CPT) Cs vapor cell atomic clock using the push-pull optical pumping technique. This method allows to detect high-contrast CPT resonances on the 0-0 magnetic-field insensitive clock transition. The clock short-term fractional frequency stability is measured to be 3e-13 s tau^(-1/2) up to 100 s averaging time, in correct agreement with the signal-to-noise ratio limit. These results are among the best performances ever reported for a CPT-based clock. The noise budget is detailed. A preliminary study is reported to evaluate limitations to the clock mid-term frequency stability. The clock performances are found to be presently mainly limited in the mid-term by laser power effects