Quantum-Fluctuation-Initiated Coherence in Multi-Octave Raman Optical Frequency Combs

We show experimentally and theoretically that the spectral components of a multi-octave frequency comb spontaneously created by stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber exhibit strong self coherence and mutual coherence within each 12 ns driving laser pulse. This coherence arises in spite of the field's initiation being from quantum zero-point fluctuations, which causes each spectral component to show large phase and energy fluctuations. This points to the possibility of an optical frequency comb with nonclassical correlations between all comb lines.Comment: Accepted for publication, Physical Review Letters, 201

Light and gas confinement in hollow-core photonic crystal fibre based photonic microcells

We review the recent progress on the understanding of optical guidance mechanisms in hollow-core photonic crystal fibres, and on the quantum and nonlinear optical applications of photonic microcells based on this fibre form. Two classes of hollow-core photonic crystal fibre are identified: one guides via a photonic bandgap and the other guides by virtue of an inhibited coupling between core and cladding mode constituents. For the former fibre type, we explore how the bandgap is formed using a photonic analogue of the tight-binding model and how it is related to the anti-resonant reflection optical waveguide guidance. For the second type of fibre, which can guide over a broad wavelength range, we examine the nature of the inhibited coupling. We describe a technique for the fabrication of photonic microcells that can accommodate vacuum pressures, and we finish by showing the latest results on electromagnetically induced transparency in a rubidium filled hollow-core photonic crystal fibre, the CW-pumped hydrogen Raman laser and the generation of multi-octave spanning stimulated Raman scattering spectral combs

Widely tunable femtosecond solitonic radiation in photonic crystal fiber cladding

We report on a means to generate tunable ultrashort optical pulses. We demonstrate that dispersive waves generated by solitons within the small-core features of a photonic crystal fiber cladding can be used to obtain femtosecond pulses tunable over an octave-wide spectral range. The generation process is highly efficient and occurs at the relatively low laser powers available from a simple Ti:sapphire laser oscillator. The described phenomenon is general and will play an important role in other systems where solitons are known to exist.Peer reviewed: YesNRC publication: N

High harmonic generation in a gas-filled hollow-core photonic crystal fiber

High harmonic generation (HHG) of intense infrared laser radiation (Ferray et al., J. Phys. B: At. Mol. Opt. Phys. 21:L31, 1988; McPherson et al., J. Opt. Soc. Am. B 4:595, 1987) enables coherent vacuum-UV (VUV) to soft-X-ray sources. In the usual setup, energetic femtosecond laser pulses are strongly focused into a gas jet, restricting the interaction length to the Rayleigh range of the focus. The average photon flux is limited by the low conversion efficiency and the low average power of the complex laser amplifier systems (Keller, Nature 424:831, 2003; Südmeyer et al., Nat. Photonics 2:599, 2008; Röser et al., Opt. Lett. 30:2754, 2005; Eidam et al., IEEE J. Sel. Top. Quantum Electron. 15:187, 2009) which typically operate at kilohertz repetition rates. This represents a severe limitation for many experiments using the harmonic radiation in fields such as metrology or high-resolution imaging. Driving HHG with novel high-power diode-pumped multi-megahertz laser systems has the potential to significantly increase the average photon flux. However, the higher average power comes at the expense of lower pulse energies because the repetition rate is increased by more than a thousand times, and efficient HHG is not possible in the usual geometry. So far, two promising techniques for HHG at lower pulse energies were developed: external build-up cavities (Gohle et al., Nature 436:234, 2005; Jones et al., Phys. Rev. Lett. 94:193, 2005) and resonant field enhancement in nanostructured targets (Kim et al., Nature 453:757, 2008). Here we present a third technique, which has advantages in terms of ease of HHG light extraction, transverse beam quality, and the possibility to substantially increase conversion efficiency by phase-matching (Paul et al., Nature 421:51, 2003; Ren et al., Opt. Express 16:17052, 2008; Serebryannikov et al., Phys. Rev. E (Stat. Nonlinear Soft Matter Phys.) 70:66611, 2004; Serebryannikov et al., Opt. Lett. 33:977, 2008; Zhang et al., Nat. Phys. 3:270, 2007). The interaction between the laser pulses and the gas occurs in a Kagome-type Hollow-Core Photonic Crystal Fiber (HC-PCF) (Benabid et al., Science 298:399, 2002), which reduces the detection threshold for HHG to only 200nJ. This novel type of fiber guides nearly all of the light in the hollow core (Couny et al., Science 318:1118, 2007), preventing damage even at intensities required for HHG. Our fiber guided 30-fs pulses with a pulse energy of more than 10μJ, which is more than five times higher than for any other photonic crystal fiber (Hensley et al., Conference on Lasers and Electro-Optics (CLEO), IEEE Press, New York, 2008

Two-color rubidium fiber frequency standard

We demonstrate an optical frequency standard based on rubidium vapor loaded within a hollow-core photonic crystal fiber. We use the 5S(1/2)→5D(5/2) two-photon transition, excited with two lasers at 780 and 776 nm. The sum-frequency of these lasers is stabilized to this transition using modulation transfer spectroscopy, demonstrating a fractional frequency stability of 9.8×10(-12) at 1 s. The current performance limitations are presented, along with a path to improving the performance by an order of magnitude. This technique will deliver a compact, robust standard with potential applications in commercial and industrial environments.C. Perrella, P. S. Light, J. D. Anstie, F. N. Baynes, F. Benabid, and A. N. Luite

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