Electromagnetically induced transparency in inhomogeneously broadened Lambda-transition with multiple excited levels

Electromagnetically induced transparency (EIT) has mainly been modelled for three-level systems. In particular, a considerable interest has been dedicated to the Lambda-configuration, with two ground states and one excited state. However, in the alkali-metal atoms, which are commonly used, hyperfine interaction in the excited state introduces several levels which simultaneously participate in the scattering process. When the Doppler broadening is comparable with the hyperfine splitting in the upper state, the three-level Lambda model does not reproduce the experimental results. Here we theoretically investigate the EIT in a hot vapor of alkali-metal atoms and demonstrate that it can be strongly reduced due to the presence of multiple excited levels. Given this model, we also show that a well-designed optical pumping enables to significantly recover the transparency

Threading plasmonic nanoparticle strings with light

This work is licensed under a Creative Commons Attribution 4.0 International License.-- et al.Nanomaterials find increasing application in communications, renewable energies, electronics and sensing. Because of its unsurpassed speed and highly tuneable interaction with matter, using light to guide the self-assembly of nanomaterials can open up novel technological frontiers. However, large-scale light-induced assembly remains challenging. Here we demonstrate an efficient route to nano-assembly through plasmon-induced laser threading of gold nanoparticle strings, producing conducting threads 12±2nm wide. This precision is achieved because the nanoparticles are first chemically assembled into chains with rigidly controlled separations of 0.9nm primed for re-sculpting. Laser-induced threading occurs on a large scale in water, tracked via a new optical resonance in the near-infrared corresponding to a hybrid chain/rod-like charge transfer plasmon. The nano-thread width depends on the chain mode resonances, the nanoparticle size, the chain length and the peak laser power, enabling nanometre-scale tuning of the optical and conducting properties of such nanomaterials.We acknowledge financial support from EPSRC grants EP/G060649/1, EP/K028510/1 and EP/L027151/1, ERC grants LINASS 320503 and ASPiRe 240629, and project FIS2010-19609-C02-01 from the Spanish Ministry of Science and Innovation. J.S.B. acknowledges the School of Physical Science, University of Cambridge, for the funding of the transmission electron microscope. S.K. acknowledges funding from the Biochemical Society (Krebs Memorial Scholarship) and the Cambridge Commonwealth Trust.Peer Reviewe

Observing Single Molecules Complexing with Cucurbit[7]uril through Nanogap Surface-Enhanced Raman Spectroscopy.

In recent years, single-molecule sensitivity achievable by surface-enhanced Raman spectroscopy (SERS) has been widely reported. We use this to investigate supramolecular host-guest chemistry with the macrocyclic host cucurbit[7]uril, on a few-to-single-molecule level. A nanogap geometry, comprising individual gold nanoparticles on a planar gold surface spaced by a single layer of molecules, gives intense SERS signals. Plasmonic coupling between the particle and the surface leads to strongly enhanced optical fields in the gap between them, with single-molecule sensitivity established using a modification of the well-known bianalyte method. Changes in the Raman modes of the host molecule are observed when single guests included inside its cavity internally stretch it. Anisotropic intermolecular interactions with the guest are found which show additional distinct features in the Raman modes of the host molecule.The authors acknowledge funding from Walters-Kundert Trust, EPSRC (EP/K028510/1, EP/G060649/1, EP/ H007024/1, ERC LINASS 320503), an ERC starting investigator grant (ASPiRe 240629), EU CUBiHOLE grant and the Defence Science and Technology Laboratory (DSTL). S.K. thanks Krebs Memorial Scholarship (The Biochemical Society) and Cambridge Commonwealth Trust for funding.This is the author accepted manuscript. The final version is available from ACS via http://dx.doi.org/10.1021/acs.jpclett.5b0253

Threading plasmonic nanoparticle strings with light.

Nanomaterials find increasing application in communications, renewable energies, electronics and sensing. Because of its unsurpassed speed and highly tuneable interaction with matter, using light to guide the self-assembly of nanomaterials can open up novel technological frontiers. However, large-scale light-induced assembly remains challenging. Here we demonstrate an efficient route to nano-assembly through plasmon-induced laser threading of gold nanoparticle strings, producing conducting threads 12±2 nm wide. This precision is achieved because the nanoparticles are first chemically assembled into chains with rigidly controlled separations of 0.9 nm primed for re-sculpting. Laser-induced threading occurs on a large scale in water, tracked via a new optical resonance in the near-infrared corresponding to a hybrid chain/rod-like charge transfer plasmon. The nano-thread width depends on the chain mode resonances, the nanoparticle size, the chain length and the peak laser power, enabling nanometre-scale tuning of the optical and conducting properties of such nanomaterials.This is the published version of the article. It was published by NPG in Nature Communications and can be found on the journal website here: http://www.nature.com/ncomms/2014/140728/ncomms5568/full/ncomms5568.html

Unexpected stability of aqueous dispersions of raspberry-like colloids

Aqueous colloidal suspensions, both man-made and natural, are part of our everyday life. The applicability of colloidal suspensions, however, is highly limited by the range of conditions over which they are stable. Here, we report a novel type of highly monodisperse ‘raspberry’ colloids, which are prepared in a single-step synthesis that relies on simultaneous dispersion and emulsion polymerisation. The resulting raspberry colloids behave almost like hard spheres. In aqueous solutions such prepared raspberries show unprecedented stability against aggregation over large variations of added salt concentrations without addition of surfactants or other stabilisers. We present simple DLVO-calculations performed on raspberries and smooth colloids showing that this stability results from our raspberries’ unique morphology preventing salt-induced colloidal aggregation, which extends our understanding of colloidal stability against salting. Our calculations are supported by salting experiments using a variety of salts and differently sized colloids with varying ‘roughness’. Further, the raspberies’ stability facilitates the formation of superspheres and thin films in which the raspberry colloids self-assemble into hexagonally close-packed photonic crystals with exquisite reproducibility.Y.L. thanks the CSC Cambridge scholarship for financial support. A.C. thanks D. Frenkel for discussions and acknowledges the ETN-COLLDENSE (H2020-MCSA-ITN-2014, Grant No. 642774). S.V. acknowledges the BBSRC David Phillips fellowship (BB/K014617/1), the European Research Council (ERC-2014-STG H2020 639088) and B. Frka-Petesic for discussions. G.G. thanks the Engineering and Physical Sciences Research Council (EPSRC, 1525292), V.E.J. the European Commission (Marie Curie Fellowship LODIS, 701455), J.L. the Marie Curie FP7 SASSYPOL ITN (607602) and M.K. EPSRC (EP/L027151/1) for financial support. E.E., Y.L. and S.V. thank the Winton Programme for the Physics of Sustainability

Unfolding the contents of sub-nm plasmonic gaps using normalising plasmon resonance spectroscopy.

Plasmonic coupling of gold nanoparticles to a gold surface creates intense plasmonic hot spots with large electromagnetic field-enhancements within the cavity formed by the two metallic surfaces. The localised field in such structures is extremely sensitive to morphological fluctuations and subtle changes in the dielectric properties of the cavity contents. Here, we present an optical method that pins down the properties of the gap contents with high sensitivity, termed normalising plasmon resonance (NPR) spectroscopy. We use this on a variety of ultrathin molecular spacers such as filled and empty cucurbiturils, and graphene. Clear differences in the spectral positions and intensities of plasmonic modes observed in the scattering spectrum resolve thickness differences of 0.1 nm, and refractive index changes from molecular filling

Life after hip fracture - Impact of home rehabilitation versus conventional care and patients' experiences of the recovery process in a short- and long-term perspective

Aim In a short- and long-term perspective compare a geriatric home rehabilitation programme (HR) for patients with hip fracture with conventional care (CC), and to capture the patients experience of the consequences of the injury and their conceptions of what influences the recovery process. Method The thesis is based on two quantitative and two qualitative studies. The two quantitative studies were randomized and controlled, longitudinal intervention studies in which 102 community-dwelling elderly patients who had received either HR (n = 48) or CC (n = 54) were followed for one year after discharge. The HR programme, which started immediately after admission to hospital, included active participation from patients in setting goals and planning discharge. The programme was focused on encouraging the participants’ self-efficacy and exercising daily activities. Assessment of balance confidence, degree of independence and frequency of daily activities, health-related quality of life, mood, perceived recovery, and basic physical performance were made one month, six months and one year after hospital discharge. In the qualitative, phenomenographic studies 18 patients were interviewed one month and one year after discharge about how they experienced the consequences of the hip fracture and their conceptions of the recovery process. Results The main recovery for all participants took place during the first six months after discharge. The results show that those who had participated in the HR programme recovered faster than those who hade received CC. Additionally, in a longer perspective they were more confident and independent than the CC group, although the differences between the groups had diminished at one year. Only 14 persons in the HR group and five persons in the CC group considered themselves fully recovered after one year. The results from the interviews showed that the hip fracture caused social and existential cracks in the individuals’ lives. The hip fracture came unexpectedly and resulted in an experience of a changed body and a more restricted life. The interviewees experienced that they had increased difficulties to move and to manage independently. One reaction was that their pre-fracture self-view as being healthy and stable had been punctured by the injury. Although positive experiences, such as being satisfied with the recovery, were also expressed, many of the negative consequences remained or had even deepened one year after discharge. A dominating experience was that they were more cautious, afraid of further falls, and felt more sedentary and isolated than before the fracture. Conclusions The results show that the negative consequences of a hip fracture are substantial and long-lasting. However, the HR programme had a more significant impact than CC on the participants’ functioning and confidence, which was most evident in the early phase of the recovery. An essential task for health care should be to create continued possibilities for rehabilitation after discharge from hospital also in a longer perspective, and not primarily focus on the medical and physical needs. The patients’ experiences and psychological reactions that may follow a hip fracture should also be considered

Self-assembly in solution of a reversible comb-shaped supramolecular polymer

We report a single step synthesis of a polyisobutene with a bis-urea moiety in the middle of the chain. In low polarity solvents, this polymer self-assembles by hydrogen bonding to form a combshaped polymer with a central hydrogen bonded backbone and polyisobutene arms. The comb backbone can be reversibly broken, and consequently, its length can be tuned by changing the solvent, the concentration or the temperature. Moreover, we have proved that the bulkiness of the side-chains have a strong influence on both the self-assembly pattern and the length of the backbone. Finally, the density of arms can be reduced, by simply mixing with a low molar mass bis-urea