Passive coherent discriminator using phase diversity for the simultaneous measurement of frequency noise and intensity noise of a continuous-wave laser

The frequency noise and intensity noise of a laser set the performance limits in many modern photonics applications and, consequently, must often be characterized. As lasers continue to improve, the measurement of these noises however becomes increasingly challenging. Current approaches for the characterization of very high-performance lasers often call for a second laser with equal or higher performance to the one that is to be measured, an incoherent interferometer having an extremely long delay-arm, or an interferometer that relies on an active device. These instrumental features can be impractical or problematic under certain experimental conditions. As an alternative, this paper presents an entirely passive coherent interferometer that employs an optical 90° hybrid coupler to perform in-phase and quadrature detection. We demonstrate the technique by measuring the frequency noise power spectral density of a highly-stable 192 THz (1560 nm) fiber laser over five frequency decades. Simultaneously, we are able to measure its relative intensity noise power spectral density and characterize the correlation between its amplitude noise and phase noise. We correct some common misconceptions through a detailed theoretical analysis and demonstrate the necessity to account for normal imperfections of the optical 90° hybrid coupler. We finally conclude that this passive coherent discriminator is suitable for reliable and simple noise characterization of highly-stable lasers, with bandwidth and dynamic range benefits but susceptibility to additive noise contamination.V Michaud-Belleau, H Bergeron, P S Light, N B Hébert, J D Deschênes, A N Luiten and J Genes

Laser-based metastable krypton generation

We demonstrate the generation of metastable krypton in the long-lived 1s^{5} state using laser excitation. The atoms are excited through a two-photon absorption process into the 2p^{6} state using a pulsed optical parametric oscillator laser operating near 215 nm, after which the atoms decay quickly into the metastable state with a branching ratio of 75%. The interaction dynamics are modeled using density matrix formalism and, by combining this with experimental observations, we are able to calculate photoionization and two-photon absorption cross sections. When compared to traditional approaches to metastable production, this approach shows great potential for high-density metastable krypton production with minimal heating of the sample. Here, we show metastable production efficiencies of up to 2% per pulse. The new experimental results gained here, when combined with the density matrix model we have developed, suggest that fractional efficiencies up to 30% are possible under optimal conditions.M. A. Dakka, G. Tsiminis, R. D. Glover, C. Perrella, J. Moffatt, N. A. Spooner, R. T. Sang, P. S. Light, and A. N. Luite

Antecedents and outcomes of consumer environmentally friendly attitudes and behaviour

With the intensification of problems relating to the environment, a growing number of consumers are becoming more ecologically conscious in their preferences and purchases of goods. This paper presents the results of a study conducted among 500 Cypriot consumers, focusing on the factors that shape consumer environmental attitudes and behaviour, as well as on the resulting outcomes. The findings confirmed that both the inward and outward environmental attitudes of a consumer are positively influenced by his/her degree of collectivism, long-term orientation, political involvement, deontology, and law obedience, but have no connection with liberalism. The adoption of an inward environmental attitude was also found to be conducive to green purchasing behaviour that ultimately leads to high product satisfaction. On the other hand, an outward environmental attitude facilitates the adoption of a general environmental behaviour, which is responsible for greater satisfaction with life. The findings of the study have important implications for shaping effective company offerings to consumers in target markets, as well as formulating appropriate policies at the governmental level to enhance environmental sensitivity among citizens

Dark soliton states of Bose-Einstein condensates in anisotropic traps

Dark soliton states of Bose-Einstein condensates in harmonic traps are studied both analytically and computationally by the direct solution of the Gross-Pitaevskii equation in three dimensions. The ground and self-consistent excited states are found numerically by relaxation in imaginary time. The energy of a stationary soliton in a harmonic trap is shown to be independent of density and geometry for large numbers of atoms. Large amplitude field modulation at a frequency resonant with the energy of a dark soliton is found to give rise to a state with multiple vortices. The Bogoliubov excitation spectrum of the soliton state contains complex frequencies, which disappear for sufficiently small numbers of atoms or large transverse confinement. The relationship between these complex modes and the snake instability is investigated numerically by propagation in real time.Comment: 11 pages, 8 embedded figures (two in color

Effects of sleep disturbance on dyspnoea and impaired lung function following hospital admission due to COVID-19 in the UK: a prospective multicentre cohort study

Background: Sleep disturbance is common following hospital admission both for COVID-19 and other causes. The clinical associations of this for recovery after hospital admission are poorly understood despite sleep disturbance contributing to morbidity in other scenarios. We aimed to investigate the prevalence and nature of sleep disturbance after discharge following hospital admission for COVID-19 and to assess whether this was associated with dyspnoea. Methods: CircCOVID was a prospective multicentre cohort substudy designed to investigate the effects of circadian disruption and sleep disturbance on recovery after COVID-19 in a cohort of participants aged 18 years or older, admitted to hospital for COVID-19 in the UK, and discharged between March, 2020, and October, 2021. Participants were recruited from the Post-hospitalisation COVID-19 study (PHOSP-COVID). Follow-up data were collected at two timepoints: an early time point 2–7 months after hospital discharge and a later time point 10–14 months after hospital discharge. Sleep quality was assessed subjectively using the Pittsburgh Sleep Quality Index questionnaire and a numerical rating scale. Sleep quality was also assessed with an accelerometer worn on the wrist (actigraphy) for 14 days. Participants were also clinically phenotyped, including assessment of symptoms (ie, anxiety [Generalised Anxiety Disorder 7-item scale questionnaire], muscle function [SARC-F questionnaire], dyspnoea [Dyspnoea-12 questionnaire] and measurement of lung function), at the early timepoint after discharge. Actigraphy results were also compared to a matched UK Biobank cohort (non-hospitalised individuals and recently hospitalised individuals). Multivariable linear regression was used to define associations of sleep disturbance with the primary outcome of breathlessness and the other clinical symptoms. PHOSP-COVID is registered on the ISRCTN Registry (ISRCTN10980107). Findings: 2320 of 2468 participants in the PHOSP-COVID study attended an early timepoint research visit a median of 5 months (IQR 4–6) following discharge from 83 hospitals in the UK. Data for sleep quality were assessed by subjective measures (the Pittsburgh Sleep Quality Index questionnaire and the numerical rating scale) for 638 participants at the early time point. Sleep quality was also assessed using device-based measures (actigraphy) a median of 7 months (IQR 5–8 months) after discharge from hospital for 729 participants. After discharge from hospital, the majority (396 [62%] of 638) of participants who had been admitted to hospital for COVID-19 reported poor sleep quality in response to the Pittsburgh Sleep Quality Index questionnaire. A comparable proportion (338 [53%] of 638) of participants felt their sleep quality had deteriorated following discharge after COVID-19 admission, as assessed by the numerical rating scale. Device-based measurements were compared to an age-matched, sex-matched, BMI-matched, and time from discharge-matched UK Biobank cohort who had recently been admitted to hospital. Compared to the recently hospitalised matched UK Biobank cohort, participants in our study slept on average 65 min (95% CI 59 to 71) longer, had a lower sleep regularity index (–19%; 95% CI –20 to –16), and a lower sleep efficiency (3·83 percentage points; 95% CI 3·40 to 4·26). Similar results were obtained when comparisons were made with the non-hospitalised UK Biobank cohort. Overall sleep quality (unadjusted effect estimate 3·94; 95% CI 2·78 to 5·10), deterioration in sleep quality following hospital admission (3·00; 1·82 to 4·28), and sleep regularity (4·38; 2·10 to 6·65) were associated with higher dyspnoea scores. Poor sleep quality, deterioration in sleep quality, and sleep regularity were also associated with impaired lung function, as assessed by forced vital capacity. Depending on the sleep metric, anxiety mediated 18–39% of the effect of sleep disturbance on dyspnoea, while muscle weakness mediated 27–41% of this effect. Interpretation: Sleep disturbance following hospital admission for COVID-19 is associated with dyspnoea, anxiety, and muscle weakness. Due to the association with multiple symptoms, targeting sleep disturbance might be beneficial in treating the post-COVID-19 condition. Funding: UK Research and Innovation, National Institute for Health Research, and Engineering and Physical Sciences Research Council

Light-shift spectroscopy of optically trapped atomic ensembles

We develop a method for extracting the physical parameters of interest for a conventional dipole-trapped cold atomic ensemble. This technique uses the spatially dependent ac-Stark shift of the trap itself to project the atomic distribution onto a light-shift broadened transmission spectrum. We develop a model that connects the atomic distribution with the expected transmission spectrum. We then demonstrate the utility of the technique by deriving the temperature, trap depth, lifetime, and trapped atom number from data that was taken in a single shot experimental measurement.Ashby P Hilton, Andre N Luiten and Philip S Ligh

Core-surround shaping of hollow-core photonic crystal fiber via HF etching

Also presented at Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference, San Jose, CA, 04 May 2008, under the title "Core-surround shaping of hollow core photonic crystal fiber via fiber etching", and published separately.We report on a technique to pattern the shape of the core surround of a hollow-core photonic crystal fiber. Different shapes are fabricated and a relationship between surface mode location and core surround thickness is experimentally observed.Y. Y. Wang, P. S. Light, and F. Benabi

Virtuaaliyhteisöjen avainmenestystekijät

Virtual communities are the big phenomenon of today. They are changing how people work, spend their free time and interact socially. Consequently, they are also an area of significant business opportunities and thus an intriguing prospect for many companies. Even though there are some remarkable success stories in the virtual community field, numerous communities have failed or the providing companies are not experiencing the expected returns. Therefore, to be able to consider building virtual communities the underlying factors for success must be determined. The research problem of this study is: "What are the key success factors of B2C virtual communities?" The objectives of the study are:. - to obtain knowledge about virtual communities and related previous research. - to identify the factors that contribute to the success of a B2C virtual community and construct a model from those factors. - to determine whether the model can be used in analyzing existing B2C virtual communities and use the process to further develop it. The extensive literature review reveals that a virtual community is a new, multi-disciplinary concept with various definitions and characteristics A fitting definition for the study is picked and a classification schema for a B2C virtual community selected. Success for a virtual community is defined and success factors discussed. The theoretical framework concerning virtual community success factors is fragmented and weak and thus by applying a grounded theory methodology, a success factor model for B2C virtual communities is built. The model consists of five interlinked success factor categories: focus, members, functionalities, business model and technical factors. To further evaluate and specify the model, three case studies are conducted. The cases include three virtual communities of the client company. They are a personal experience sharing community, a gaming community and a concept for a wide-scope consumer community. Analyzing the case studies leads to verification of the model and to the addition of an important factor "goals and measuring" to the business model category. The model thus portrays the key success factors of B2C virtual communities. Finally, recommendations are given to the client company concerning the analyzed communities, the whole virtual community domain and the usage of the key success factor model. The findings of the research have been applied throughout an ambitious project in the client company, thus proving their applicability and significance.Virtuaaliyhteisöt ovat tämän päivän suuri ilmiö. Ne ovat muuttamassa sitä, miten ihmiset työskentelevät, käyttävät vapaa-aikansa ja kanssakäyvät sosiaalisesti. Tästä johtuen ne ovat myös alue merkittäville liiketoimintamahdollisuuksille ja siksi kiehtova mahdollisuus yrityksille. Vaikka on olemassa joitain merkittäviä menestystarinoita virtuaaliyhteisöjen alalla, lukuisat yhteisöt ovat epäonnistuneet tai niitä tarjoavat yritykset eivät saa niistä odotettuja tuottoja. Jotta pystytään harkitsemaan virtuaaliyhteisöjen rakentamista, niiden perustana olevat menestyksen tekijät pitää määrittää. Tutkimusongelma, johon tutkimus vastaa on: "Mitkä ovat yritysten kuluttajille tarjoamien virtuaaliyhteisöjen avainmenestystekijät?" Tutkimuksen tavoitteet ovat:. - hankkia tietoa virtuaaliyhteisöstä ja niihin liittyvästä aiemmasta tutkimuksesta. - tunnistaa tekijät, jotka myötävaikuttavat yritysten kuluttajille tarjoamien (B2C) virtuaaliyhteisöjen menestykseen ja rakentaa malli näistä tekijöistä. - määrittää voiko mallia käyttää B2C virtuaaliyhteisöjen analysoimiseen ja edelleen käyttää tätä prosessia mallin kehittämiseen. Laaja kirjallisuuskatsaus paljastaa, että virtuaaliyhteisö on uusi poikkitieteellinen konsepti, jolla on lukuisia määritelmiä ja ominaisuuksia. Tutkimusta varten valitaan sopiva määritelmä virtuaaliyhteisöille ja luokittelukaavio B2C virtuaaliyhteisöille. Menestys määritellään ja menestystekijöistä keskustellaan. Virtuaaliyhteisöjen menestystekijöihin liittyvä teoreettinen viitekehys on hajanainen ja heikko, ja siksi grounded theory -metodologiaa käyttäen rakennetaan B2C virtuaaliyhteisöjen menestystekijämalli. Malli koostuu viidestä toisiinsa liittyneestä kategoriasta: fokus, jäsenet, toiminnallisuudet, liiketoimintamalli ja tekniset tekijät. Mallin arviointia ja tarkennusta varten suoritetaan kolme tapaustutkimusta, jotka muodostuvat kolmesta asiakasyrityksen tarjoamasta virtuaaliyhteisöstä. Ne ovat henkilökohtaisten kokemuksien jakamiseen tarkoitettu yhteisö, peliyhteisö ja konsepti laaja-alaiselle kuluttajayhteisölle. Tapausten analysointi johtaa mallin vahvistamiseen ja tärkeän tekijän "maalit ja mittaaminen" lisäämiseen liiketoimintamalli-kategoriaan. Kokonaisuudessaan malli esittää B2C virtuaaliyhteisöjen avainmenestystekijät. Lopuksi annetaan suosituksia asiakasyritykselle liittyen analysoituihin yhteisöihin, koko virtuaaliyhteisöjen alueeseen ja avainmenestystekijämallin käyttöön. Tutkimuksen löydöksiä on käytetty eräässä asiakasyrityksen kunnianhimoisessa projektissa, mikä todistaa niiden soveltuvuuden ja merkityksen

Spectral broadening of a single-photon transition in the evanescent field of an exposed-core fiber

We theoretically and experimentally examine the spectroscopy of warm atoms traversing the evanescent field of a guided mode in silica glass. The subwavelength scale of the evanescent field leads to a large spectral broadening dominated by transit-time dephasing, creating a lineshape quite different from that of atoms in free space, and also distinct from that arising from transit-time-limited interactions in a field with a Gaussian intensity profile. We show reasonable agreement between our modeling of this scenario and experimental D2-line spectra obtained from an exposed-core fiber immersed in rubidium vapor.H.P. Griesser, C. Perrella, P.S. Light and A.N. Luite

Dual-color magic-wavelength trap for suppression of light shifts in atoms

We present an optical approach to compensating for spatially varying ac-Stark shifts that appear on atomic ensembles subject to strong optical control or trapping fields. The introduction of an additional weak light field produces an intentional perturbation between atomic states that is tuned to suppress the influence of the strong field. The compensation field suppresses sensitivity in one of the transition frequencies of the trapped atoms to both the atomic distribution and motion. We demonstrate this technique in a cold rubidium ensemble and show a reduction in inhomogeneous broadening in the trap. This two-color approach emulates the magic-trapping approach that is used in modern atomic-lattice clocks but provides greater flexibility in choice of atomic species, probe transition, and trap wavelength.A.P. Hilton, C. Perrella, A.N. Luiten, and P.S. Ligh