Search

Photonics-based quantum information technologies require efficient, high emission rate sources of single photons. Position-controlled quantum dots embedded within a broadband nanowire waveguide provide a fully scalable route to fabricating highly efficient single-photon sources. However, emission rates for single-photon devices are limited by radiative recombination lifetimes. Here, we demonstrate a multiplexed single-photon source based on a multidot nanowire. Using epitaxially grown nanowires, we incorporate multiple energy-tuned dots, each optimally positioned within the nanowire waveguide, providing single photons with high efficiency. This linear scaling of the single-photon emission rate with number of emitters is demonstrated using a five-dot nanowire with an average multiphoton emission probability of

BACKGROUND: The acute vascular disease deep vein thrombosis (DVT) requires oral anticoagulants to prevent progression. Monitoring therapeutic efficacy of direct oral anticoagulants (DOAC), including rivaroxaban, is problematic as no reliable test is available. Advances in rheometry have led to the development of a functional coagulation biomarker using Gel Point (GP) analysis which assesses clot structure formation. The biomarker measures incipient clot formation time (TGP) and quantifies fibrin clot structure in terms of fractal dimension (df). OBJECTIVE: This study aimed to investigate clot structure formation in first time DVT and the effect of rivaroxaban treatment. METHODS: This prospective observational cohort study measured the GP and standard laboratory markers at three sample points: pre-treatment and at 20 and 60 days following 15 mg BD and 20 mg OD rivaroxaban respectively. RESULTS: Forty DVT patients (mean age 64 years [SD±14.8]; 23 males, 17 female) were recruited. The results show that DVT vs non-DVT patients did not have a significantly different GP profile (df: 1.72±0.06 vs 1.70±0.06 and TGP: 267±68 sec vs 262±73 sec) with both within the defined healthy index. In addition, rivaroxaban therapy increased TGP to 392 s (±135 s) after 20 days, and subsequently increased to 395 s (±194 s) at 60 days but did not significantly increase df (from 1.69±0.05 to 1.71±0.06). CONCLUSIONS: The results indicate in this cohort of DVT patients there was no underlying hypercoagulable effect as determined by gel point analysis. Furthermore, the anticoagulant effect of rivaroxaban prolonged clotting, suggesting a protective effect against clot formation, without significantly reducing clot microstructural properties.

HypothesisOur central hypothesis is that inhibition of Schwann cell de-differentiation, in the post-injury setting, will reduce synkinesis and improve facial muscle functionBackgroundNo therapies exist to improve the accuracy of facial nerve regeneration. Following peripheral nerve injury, adult reactive Schwann cells de-differentiate and express glial fibrillary acidic protein (GFAP); suggesting that reactive Schwann cells impact axonal regeneration precision.MethodsTransgenic GFAP-thymidine kinase (TK) mouse model was employed, allowing selective downregulation of reactive GFAP expressing Schwann cells on exposure of 7 day osmotic pump delivery of ganciclovir. Adult female transgenic GFAP-TK mice had right facial nerve transected and then immediately repaired with tissue glue, they then either were treated with saline or ganciclovir (GCV). At 6 weeks post-injury, mice were exposed to random air puffs events while high speed videography recorded whisker and eye movement. MatLab code video processing with publicly available BIOTACT algorithm automatically tracked whiskers.ResultsWhisker velocity was calculated using binning statistical analysis. Saline treated animals confirmed our model’s ability to detect aberrant movement such that intact (left) facial nerves caused whisker protraction, while repaired (right) facial nerves had retraction. Administration of GCV increased whisker retraction compared to saline. GCV did not impact intact animal whisker movement compared to repaired whiskers.ConclusionsInhibition of reactive Schwann cell proliferation appears to worse the degree of synkinesis, providing important insight into a potential therapeutic target for facial nerve injury.

Abnormal clot microstructure plays a pivotal role in the pathophysiology of thromboembolic diseases. Assessing the viscoelastic properties of clot microstructure using novel parameters, Time to Gel Point (T GP ), Fractal Dimension (d f ) and clot elasticity (G׳ GP ) could explain the increased cardiovascular and thromboembolic events in patients with Obstructive Sleep Apnoea Hypopnea Syndrome (OSAHS). We wanted to compare T GP , d f , and G׳ GP and their diurnal variation in OSAHS and symptomatic comparators. thirty six patients attending a sleep disturbed breathing clinic with symptoms of OSAHS were recruited. T GP , d f and G׳ GP were measured alongside standard coagulation screening, thrombin generation assays, and platelet aggregometry at 16:00 h and immediately after an in-patient sleep study at 07:30 h. OSAHS group had significantly lower afternoon d f than comparators (1.705±0.033 vs. 1.731±0.031, p

Background The long term benefits of exercise on the cardiovascular status of a patient have been proven, however, their benefit/risk relationship with exercise intensity is unclear. Furthermore, many thromboembolic diseases such as myocardial infarction and ischaemic stroke are associated with profound catecholamine release. In this study we explore the relationship between catecholamine release and hemodynamic changes and their effect on coagulation. Materials and methods Twelve healthy recreationally active males were recruited. Local anesthesia was given and catheters were placed under aseptic conditions, in the femoral artery and vein of the experimental leg. The first experiment involved tyramine infusion into the femoral artery at a dose of 1.0 μmol·min−1·L leg volume−1. The second experiment involved single leg knee-extensor exercise performed at 30 W for 15 min. Venous blood was collected at each time point to assess clot microstructure using the df biomarker. Results and conclusions Tyramine infusion causes a local noradrenaline release in the leg. The increase in noradrenaline was associated with a significant increase in clot microstructure formation (df increased from 1.692 ± 0.029 to 1.722 ± 0.047, p = 0.016). Additionally moderate intensity single leg knee extensor exercise, which minimally alters sympathetic activity, also induced an increases in df (from 1.688 ± 0.025 to 1.723 ± 0.023, p = 0.001). This suggests that exercise can alter clot microstructure formation both via an increase in catecholeamine levels and by factors related to muscle activity per se, such as increased blood flow and consequent shear. These findings have implications for recommendations of exercise in patients at risk of cardiovascular events.

The study purpose was to define changes in coagulation across the sepsis spectrum using rotational thromboelastometry (ROTEM).Sepsis patients were recruited on admission to the Emergency Department and Intensive Care Units of a large teaching hospital in Wales. ROTEM markers of clot development and fibrinolysis were determined, as well as standard coagulation markers. A healthy control group matched for age and gender was also recruited (n=44).100 patients were recruited (50 sepsis, 20 severe sepsis and 30 septic shock). Maximum clot firmness was significantly higher in the sepsis (p0.001) and severe sepsis (p=0.012) groups than the healthy control (71.6±4.5 and 70.4±4.1 vs 64.4 respectively). In septic shock there was prolonged clot development; however, maximum clot firmness remained normal. Fibrinolytic function was significantly impaired in septic shock, which was also significantly associated with 28-day mortality (p0.001).ROTEM indicated significantly enhanced clot structural development in sepsis and severe sepsis, which could be indicative of a hypercoagulable phase. In septic shock, despite there being a prolongation of clotting pathways and impaired fibrinolysis, clot mass was comparably normal, suggestive of the development of a clot with healthy characteristics.

Sepsis and its progression are known to have a major influence on the coagulation system. Current coagulation tests are of limited use when assessing coagulation in sepsis patients. This study aims to assess the potential for a new functional biomarker of clot microstructure, fractal dimension, to identify changes in the mechanical properties of clot microstructure across the sepsis spectrum (sepsis, severe sepsis and septic shock). A total of 100 patients that presented acutely to a large teaching hospital were included in this prospective observational study (50 sepsis, 20 severe sepsis and 30 septic shock) against a matched control of 44 healthy volunteers. Fractal analysis was performed, as well as standard markers of coagulation, and six plasma markers of inflammation. Fractal dimension was significantly higher in the sepsis and severe sepsis groups than the healthy control (1.78 ± 0.07 and 1.80 ± 0.05, respectively vs 1.74 ± 0.03) (p

We report the results of experiments designed to test the hypothesis that the enhanced levels of extensional viscosity conferred upon a liquid due to a polymer additive substantially mitigate cavitation damage, in addition to substantially increasing the liquid's cavitation threshold stress. As far as we are aware, these issues have never been directly addressed in a single investigation, involving samples of the same polymer system, in complementary experiments expressly designed for these purposes. The cavitation thresholds of aqueous PAA solutions are measured under dynamic stressing by pulses of tension and cavitation erosion experiments involving solid target specimens are also reported. The cavitation threshold of the solutions is found to be substantially enhanced by the presence of the polymer and the damage patterns recorded by scanning electron microscopy after 80 min exposure to cavitation in polymer solutions differ significantly from those in water. Whereas in water the surface presents heavily eroded areas with deep pitting cavities, in the 1% PAA solution the damage appears only in the form of individual craters that accumulate along specific lines and large undamaged areas (a stringy damage pattern). The weight loss decreases with increasing the polymer concentration and is one order of magnitude smaller in the 1% PAA solution than in the case of water. The present results suggest that the reduction of the maximum pressure inside the bubble at its minimum volume upon addition of polymer is the dominant mechanism of the observed suppression of cavitation damage in polymer solutions. The implications of the results are discussed with respect to the reduction of collateral damage in ultrasound phacoemulsification.

Objectives. Work-related upper limb disorders (WRULD) are common and disabling complaints in industry, but a tissue diagnosis can be difficult where the pain is diffuse and variable, and this prevents effective treatment. Diffuse arm pain is frequently found in those doing rapid or strenuous repetitive work, such as factory assembly workers or keyboard operators. Similar symptoms occur in the legs in athletes, where chronic compartment syndrome (CCS) is a recognized entity, so we investigated the possibility that this might also be caused by prolonged repetitive work. Methods. Patients were selected if they were unable to continue with work because of chronic forearm pain. They were divided into three groups: 42 patients with symptoms consistent with CCS as defined in the text, 15 volunteers and patients with other arm complaints, and 10 asymptomatic arms of patients with unilateral CCS. We measured the pressure inside the extensor muscle compartment of the forearm at rest and after a 2 min repetitive gripping exercise using an electronic pressure-sensitive probe. Results. The results show that CCS is a common and disabling forearm complaint associated with prolonged repetitive work. Fifteen patients have now had decompressive surgery on the extensor muscle compartment with good relief of symptoms. Conclusion. CCS is responsible for chronic peripheral neurological dysfunction in addition to muscle pain, and awareness of this diagnosis allows early identification and treatment of a currently unrecognized disorder with potential resolution of a long-lasting arm disability.

We discuss the preparation and spectroscopic characterisation of a single InAs/InP quantum dot suitable for long-distance quantum key distribution applications around λ=1.55 μm . The dot is prepared using a site-selective growth technique which allows a single dot to be deposited in isolation at a controlled spatial location. Micro-photoluminescence measurements as a function of exciton occupation are used to determine the electronic structure of the dot. Biexciton emission, shell filling and many-body re-normalization effects are observed for the first time in single InAs/InP quantum dots.

This paper reports the first measurements of the effective tensile strength (or ‘cavitation threshold’) Fc, of degassed samples of a commercial multigrade engine oil over a range of temperatures, T, which are representative of those encountered under normal automotive engine operating conditions (in the range 20° C ≤ T ≤ 140°C). Also reported are the values of Fc obtained for Newtonian silicone oils over a range of shear viscosities. In the experiments reported herein, samples of liquid are subjected to dynamic stressing by a rapid pressure—tension cycle, this being a feature of the conditions experienced by an engine oil within a dynamically loaded journal bearing. The method used herein to estimate Fc avoids reliance upon direct measurements of substantial dynamic negative pressures using transducers which are designed for use in the range of positive pressures.

Suicide prevention remains an important objective for the mental health services. The mentally ill represent a group of individuals at increased risk of suicide and, understandably, efforts have been made to ensure high quality care provision to prevent such acts. Audit of clinical practice is an important tool to monitor the efficacy of services and to improve their performance, and here the workings of a multidisciplinary suicide audit process within an inner city general mental health service are described.

This paper addresses discrepancies between the results of different measurements of the effective tensile strength (Fc) of liquids, in experiments in which a pulse of tension (or `negative pressure') is created by the reflection of a pressure pulse at a suitable boundary. We show that a key feature of the pressure records previously reported in such experiments may have been misinterpreted. The first complete account of such pressure records reported here offers an explanation for the order-of-magnitude discrepancies in Fc which arise in work involving instruments such as the `Bullet-Piston' (B-P) pulse-reflection apparatus (Temperley H N V and Trevena D H 1987 J. Phys. D: Appl. Phys. 20 1080). We also report a new method of estimating Fc in a modified B-P apparatus and the results obtained indicate that samples of degassed, deionized water can sustain tensions which are an order-of-magnitude greater than previously reported in B-P work. Results are also reported for work involving samples of Newtonian silicone oils, for which the dependence of Fc on shear viscosity, µ, found in this work confirms that of an earlier study although the absolute values of Fc are found to be considerably greater than previously reported.

We report theoretical and experimental work which demonstrates how the viscoelastic dispersion of shear waves may be exploited in studies of the rheological properties of systems such as 'critical-gels' - systems at the gel point. At the gel point a material undergoing gelation changes, from one in which only short range connectivity is present, to one in which structural self-similarity is sample-spanning. Experiments are described in which marked changes in high-frequency shear-wave dispersion are recorded during the viscoelastic-liquid to viscoelastic solid transition about the gel point. The results accord with theoretical treatments of the sol-gel transition, based on a modified form of the Gross-Marvin network model. We report how this modified model has been used to investigate the interdependence of the high- and low-frequency features of the evolving relaxation time spectra associated with the growth of discrete, mechanically self-similar nodal networks. An analysis of the growth of the networks reveals a scale-invariant characteristic of the underlying gel microstructure and an associated fractal dimension, d f , in the range 1 < d f < 1.8, the maximum value of which corresponds to that reported in computer simulations of cluster-cluster' aggregation processes. The limitations of conventional rheometry in identifying the inner cut-off' length scale of such a fractal characteristic are discussed. Shear wave dispersion measurements are also reported for aqueous dispersions of a synthetic clay colloid which, like the simulated viscoelastic networks, combines the characteristics of high-shear elasticity and low-wave attenuation with a maximum fractal dimension of 1.8.

The incidence of tuberculosis has ceased to decline in the developing world and in some parts of the developed world. This is thought to result mainly from the increased prevalence of human immunodeficiency virus infection and the development of multidrug-resistant strains of Mycobacterium tuberculosis. In addition, it is increasingly presenting in atypical sites and in an atypical manner. However, a high index of suspicion can overcome these diagnostic difficulties and enable early appropriate treatment to produce excellent results. We report a case of isolated tuberculous osteomyelitis of the bones of the hindfoot of a 41-year-old man that proved difficult to diagnose but which responded very well to chemotherapy.

We provide an explanation for the anomalously low values of liquid tensile strength recorded in some experiments involving the reflection of a pressure pulse (as tension) at the free surface of a column of water, or at a flexible membrane. The present work, which involves a development of the ‘bullet–piston’ method of subjecting a liquid to tension, reconciles previous dynamic stressing results with those obtained for water in a steel Berthelot tube under static stressing. It is shown that the anomalously low values of liquid tensile strength cannot be explained in terms of the effect of the free–surface transition layer in pulse reflection (as was previously thought) but may be attributed to deficiencies in the techniques previously used to record dynamic tensions.

A study of viscoelastic shear wave dispersion in a simulated gelation process involving mechanically self-similar nodal networks is reported. The network formed at the gel point (the infinite network cluster, or `critical gel') shares a common structural feature of smaller network clusters and the onset of a recognizably `gel-like' feature is shown to occur when the characteristic wavelength of the network cluster becomes twice that of an individual node. It is shown that, during gelation, the dispersion of shear waves can be exploited to assess the proximity of a system to an equivalent `critical gel' state at any single frequency, thereby identifying the smallest length scale at which gel-like characteristics are established prior to the gel point. In this way, and for the first time, a rheometrical basis is established for examining the gel-like, self-similar characteristics of pre-gel point viscoelastic liquid systems, in terms of the gel equation but in the absence of a frequency-independent loss tangent. Experiments are reported for a critical gel in which the high-frequency wave dispersion is in good agreement with theory.

The index of refraction for pseudomorphic Si/sub 1-x/Ge/sub x/ layers grown on Si has been measured at wavelengths /spl lambda/=1310 mn and /spl lambda/=1550 nm. The refractive index values were obtained from waveguide mode profile measurements on a series of Si-Si/sub 1-x/Ge/sub x/-Si waveguides with Ge/sub x/ concentrations between x=0.01 and x=0.1. The index of refraction, n, is significantly larger for light polarized parallel to the growth direction than for light polarized in the plane of the epilayer. This birefringence is consistent with the anisotropic index change predicted using photoelastic theory, given the biaxial strain present in the pseudomorphic Si/sub 1-x/Ge/sub x/ layers. At all wavelengths and polarizations, n varies linearly with the Ge concentration. The pseudomorphic Si/sub 1-x/Ge/sub x/ waveguides layer are stable against lattice relaxation during short anneals at 950/spl deg/C, but exhibit partial relaxation after annealing at 1200/spl deg/C.

Male Sprague-Dawley rats (200–250 g) were segregated into 12 groups (n =5). Six groups were injected with morphine sulphate (10,20,30,50 mg/kg,ip) on days 1, 2, 3 and 4 respectively. The specified dose of morphine was given in two divided doses daily at 1000 h (light) and 2200 h (dark) for four consecutive days. The remaining six groups received saline. On day 5, the rats from saline and morphine treated groups were injected with naloxone (50 mg/kg, ip) at 0600 h, 1000 h, 1400 h, 1800 h, 2200 h, or 0200 h to precipitate the withdrawal signs during the light and dark phases of the 24 h period. Withdrawal signs were monitored for the following 30 min. Diarrhea, tremor, teeth chattering and crying (vocalization) were exhibited exclusively by the morphine-dependent rats. Escape attempts and restless activity were observed mostly in morphine-dependent groups, except for a limited response by controls at 0200 h or 0600 h. The percentage response of other signs such as hunch-back posture, piloerection, stereotyp...

A study of shear wave dispersion in a gelling system shows that marked changes in dispersion occur due to the viscoelastic liquid to viscoelastic solid transition. A theoretical study suggests that an immediate pre-gel combination of liquid-like and solid-like properties might be detected by shear wave dispersion measurements. Experimental work on a system which exhibits critical gel behaviour gives a high frequency wave dispersion in good agreement with theoretical predictions. The work illustrates the interdependence of the development of the relaxation spectrum at low frequencies and the high frequency wave dispersion, and suggests that measurements of the latter might be used to determine the gel-point in some systems.

We discuss the design, fabrication and characterisation of optical microcavities suitable for application with single, site-selected InAs/InP quantum dots emitting around λ =1550 nm. The fabrication procedures that we employ allow high finesse cavities to be constructed around single quantum dots with a known nucleation site and ground state emission energy. Two types of cavity are explored: (i) pillar cavities in which the quantum dot can be located within the semiconductor spacer layer between two dielectric Bragg reflectors and (ii) photonic bandgap cavities employing textured InP membranes. For 1 μm diameter, SiO 2 /Ta 2 O 5 pillar cavities we obtain cavity quality factors, Q , of 1500 and for membrane cavities, Q values of 850.

In this report, we present data on an InGaAs/GaAs strained single quantum well laser with the lowest reported threshold current density to date, namely 44 A cm−2 for a 3 mm cavity length. This was grown by solid-source molecular-beam epitaxy with the arsenic dimer, As2. The structure is that of a graded-index, separate-confinement heterostructure with a single strained InGaAs quantum well, sandwiched between GaAs barrier layers and AlGaAs cladding layers. The wavelength of the lasers was around 985 nm, and the internal efficiency and losses were 69% and 0.70 cm−1, respectively. In addition, data on the uniformity of our lasers, which are grown on rotating 2 in substrates (1 in = 2.54 cm), show drops in photoluminescence emission wavelength and layer thickness of less than 4 nm and 4%, respectively, from the centre to the edge of the wafer and very little compositional change.

Patients with rheumatoid arthritis who underwent excision of the distal ulna were reviewed and the operated wrist was compared with the non-operated side in the 40 patients who had the procedure performed unilaterally. Radiological assessment showed that the radiocapitate measurement of carpal translocation was the most consistent and that excision of the distal ulna was not associated with statistically significant collapse, ulnar translocation or radial rotation of the carpus. 61% of wrists spontaneously developed a radial shelf or limited radiocarpal fusion following excision of the distal ulna, compared to 21% of non-operated wrists. However, there was no statistically significant difference in carpal collapse or ulnar translocation between these two groups.

A 1-year-old female infant presented with a large 7-8 cm Ewing's sarcoma of the left parietal calvarium. It deeply indented the subjacent hemisphere. Wide surgical excision was followed by chemotherapy but not radiation. The patient was clinically free of tumor when she expired 9 months later of sepsis. Though primary Ewing's sarcoma of the skull is said to be relatively rare, we have tabulated 37 cases of this disorder, including the present one (we excluded mandibular tumors (> 100 cases) since they are not usually treated by neurosurgeons). The mean age was 11 years and of those available to follow-up, three quarters were tumor-free 6 months to 7 years postsurgery. The remainder survived an average of 21 months. Ewing's tumors of the calvarium generally grant a favorable prognosis following surgery and/or radiation and chemotherapy. Those at the base of the brain may be more difficult to eradicate. In addition to primary Ewing's tumors, metastases to the skull and the brain from other primary sources in the skeleton have been documented in several reports.

While reading an orthopaedic text you find a table that states rib fractures are highly specific for non-accidental injury in children. No papers are referenced and you wonder what evidence exists to support this statement. ### Structured clinical question In children undergoing chest radiography [patients] are rib fractures on plain radiographs [test] specific for non-accidental injury [outcome]? ### Search strategy and outcome #### Secondary sources Cochrane: rib fractures and non-accidental injury; no relevant reviews found. #### Primary sources Medline (including Medline corrections) 1966–01/02/2004. [(Validated paediatric search filter (March 2003) for Ovid1) AND (exp Child Abuse or non-accidental injury.mp or child abuse$.mp or deliberate injury.mp or exp. domestic violence or child abuse, sexual or exp. Munchausen syndrome by proxy or exp torture or domestic violence.mp or Munchausen syndrome by proxy.mp. or torture.mp or non-accidental injuries.mp) and (exp.rib fractures or rib fracture$.mp or posterior rib fracture$.mp or multiple rib fracture$.mp or bilateral rib fracture$.mp or exp. thoracic injuries or thoracic injury.mp or chostochondral junction injuries.mp)] limited to human and English Language. A total of 113 papers were identified; 105 were of insufficient quality for inclusion or irrelevant. One paper was subsequently excluded …

The Polar Ionospheric X-ray Imaging Experiment (PIXIE) is an X-ray multiple-pinhole camera designed to image simultaneously an entire auroral region from high altitudes. It will be mounted on the despun platform of the POLAR spacecraft and will measure the spatial distribution and temporal variation of auroral X-ray emissions in the 2 to 60 keV energy range on the day side of the Earth as well as the night. PIXIE consists of two pinhole cameras integrated into one assembly, each equipped with an adjustable aperture plate that allows an optimum number of nonoverlapping images to be formed in the detector plane at each phase of the satellite's eccentric orbit. The aperture plates also allow the pinhole size to be adjusted so that the experimenter can trade off spatial resolution against instrument sensitivity. In the principal mode of operation, one aperture plate will be positioned for high spatial resolution and the other for high sensitivity. The detectors consist of four stacked multiwire position-sensitive proportional counters, two in each of two separate gas chambers. The front chamber operates in the 2–12 keV energy range and the rear chamber in the 10–60 keV range. All of the energy and position information for each telemetered X-ray event is available on the ground. This enables the experimenter to adjust the exposure timepostfacto so that energy spectra of each X-ray emitting region can be independently accumulated. From these data PIXIE will provide, for the first time, global images of precipitated energetic electron spectra, energy inputs, ionospheric electron densities, and upper atmospheric conductivities.

Planar InAs/InP quantum-dot microcavities using multilayer SiO2/Ta2O5 Bragg reflectors have been studied in emission. For an eight-pair mirror design, the stop band extends from 700 to 900 meV and the cavity linewidth is ∼500 μeV for emission at 850 meV. Measurements as a function of incident power show quantum-dot saturation behavior, with the emission intensity going to the wetting layer outside the cavity stop band. Saturation behavior at fixed pump power is also observed as a function of decreasing temperature. Dispersion measurements as a function of emission angle show polarization splitting in reasonable agreement with theory.

This Letter introduces an enhanced cavity-waveguide coupling architecture based upon slow-light engineering in a two-port photonic crystal system. After analyzing the system transmittance using coupled-mode theory, the system is probed experimentally and shown to have increased transmittance due to the enhanced cavity-waveguide coupling. Such a coupling architecture may facilitate next-generation planar lightwave circuitry such as onchip quantum information processing or high precision light-matter sensing applications.

The ability to control the nucleation site of a single quantum dot will have a profound effect on the development of quantum dot-based photonic devices. The deterministic approach will provide a truly scalable technology that can take full advantage of conventional semiconductor processing for device fabrication. In this review, we discuss the progress towards the integration of deterministically nucleated single quantum dots with top-down quantum optical devices targeting telecommunication wavelengths. Advances in site-controlled quantum dot nucleation using selective-area epitaxy now makes it possible to position quantum dots at predetermined positions on a substrate in registry with alignment markers. This, in turn, has allowed for devices fabricated in subsequent processing steps to be aligned to individual quantum dots. The specific devices being targeted are gated-single dots and coupled dot-cavity systems which are key components of efficient sources of single photons and entangled photon pairs.

This chapter contains sections titled: Introduction Directed self-assembly Spectroscopic signatures Application of electric fields Optical cavities Conclusions

We demonstrate precise control of electron charging within a single deterministically positioned InAs/InP quantum dot emitting in the telecommunications band around 1500 nm. Photolumine-scence emission as a function of vertical electric field is used to monitor the electron number within the dot. From Stark shift spectroscopy, we extract strength and orientation for the built-in dipole moment that suggests a uniform InAs dot composition and a configuration in which the electron lies above the hole at zero electric field. The scalable gating technology we employ to electrically contact individual prepositioned quantum dots promises arrays of initialized single spins that can be used for fiber-based quantum information applications.

Preliminary experimental spectral photoconductivity, time-resolved photoconductivity and non-linear optical absorption data are presented which demonstrate that NIPI structures have been produced in InSb for the first time. The measured band gap reduction and lifetime enhancement effects are in excellent agreement with the predictions of the authors' theoretical model and indicate a clear potential for these structures as high-performanceIR detectors.

In situ reflection high‐energy electron diffraction and cross‐sectional and plan‐view transmission electron microscopy have been used to investigate the initial stages of InSb growth on GaAs(001), by molecular‐beam epitaxy. Growth of the InSb commences with the formation of rectangular‐based islands, having flat tops and sloping sides, with facets on certain planes of types {111} and {113}. The islands show near normal lattice spacings, with no significant straining. As deposition proceeds, islands coalesce and, after the equivalent of 40 monolayers of deposition, form a connected network. Complete coverage of the GaAs substrate is achieved after ≂300 monolayers of deposition. This places a lower limit on the thickness of InSb layers, which may be considered in the design of optoelectronic devices.

The second harmonic radiation emitted into the top half space from three dimensionally localized modes of L3 defect cavities in InP-based planar photonic crystals is studied using both CW and pulsed excitation. The far field harmonic radiation patterns observed from modes with resonant wavelengths ~ 1550 nm, excited by a tunable CW laser with less than 1 mW power, reveal strong local field enhancement (> 1000 X). A detailed comparison with FDTD modeling allows us to conclude that the bulk InP second order susceptibility tensor dominates the second order response of these microcavities. When a broadband, sub picoseconds source is used to simultaneously excite two of the microcavity modes, the harmonic spectrum in general consists of three contributions, the second harmonic from each of the excited modes, and a third peak due to the second order (sum frequency) mixing of the two modes. By using short and long pulse excitation simultaneously, we demonstrate how the emission frequency due to sum frequency processes can be used to continuously tune the harmonic emission frequency dependent on the occupation of various cavity modes.

We present an experimental investigation of the localised optical defect modes in hexagonal symmetry, single missing hole defect, InP membrane, photonic crystal microcavities. An InAs/InP quantum dot ensemble is located at the midpoint of the InP membrane to allow characterisation of the optical modes in emission. Simple modifications to the cavity configuration are used to split the degeneracy of the orthogonally polarised x- and y-dipole cavity modes and to introduce a higher energy mode into the cavity with cavity quality factor Q up to 2,800.

We examine the optical mode structure of two-dimensional, photonic crystal microcavities based on triple missing hole defects in hexagonal symmetry, etched air-hole, suspended InP membranes. Polarisation dependent photoluminescence from InAs/InP quantum dots embedded within the cavities is used to explore mode energies and quality factors, Q, as a function of cavity design parameters. Optimised Q values are in excess of 7,500 for the modified y-dipole mode. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Using photoluminescence we have studied the effect of a low temperature ‘‘preanneal’’ stage on the intermixing of 3 nm Si0.7Ge0.3/Si quantum wells, implanted with silicon ions having energies up to 1 MeV and then exposed to rapid thermal annealing at 850 °C for 300 s. We find that an unwanted quantum well band gap increase in unimplanted samples after rapid thermal annealing can be reduced substantially from ∼30 to ∼5 meV due to the removal of grown‐in defects by preannealing at 630 °C for 24 h. Preannealed samples that were implanted and rapid thermal annealed showed at least the same band gap increase (up to 70 meV in these samples) observed for nonpreannealed samples. These results are understood in terms of significantly different activation energies for defect diffusion and quantum well intermixing and a nonlinear dependence of the energy shifts on defect concentrations.

A filtered imager, the CONTOUR Forward Imager (CFI), was designed, fabricated, and qualified for the Comet Nucleus Tour (CONTOUR) Discovery class mission. The CONTOUR spacecraft was launched July 3, 2002, and failed during injection to heliocentric orbit on August 15, 2002. This paper provides an overview of the efforts to produce CFI. The CFI imager was designed to perform optical navigation, comet nucleus imaging, and comet coma imaging. CFI was complemented in the CONTOUR payload by the CONTOUR Remote Imager and Spectrometer (CRISP). The emphasis in the CFI design was on high sensitivity at moderate to long ranges from the comet nucleus, while CRISP was designed for high-speed observations in close to the nucleus. A unique aspect of CFI was the requirement to image multiple comets after being exposed to high-velocity cometary dust on the previous comet flybys (which damages and contaminates the forward looking optics). The first optical surface was replaceable between comet encounters, using a mirror "cube" mechanism, to alleviate the dust damage. Another challenging aspect of the design is that the spacecraft was thruster stabilized (no reaction wheels), placing limits on the available exposure time to accomplish the high sensitivity observations required. CFI utilized ten filters covering from 300 to 920 nm to image onto a backthinned 1024 by 1024 element CCD. The Ritchie-Chrietien telescope provided a clear aperture of 62 mm, a full field of view of 2.5 degrees, and a pixel field of view of 43 microradians. CFI was designed and fabricated by a combined effort of the Johns Hopkins University Applied Physics Laboratory and SSG Precision Optronics. The CONTOUR mission was lost prior to CFI being powered on in flight.

We present optical spectroscopy measurements on a single InAs/InP quantum dot emitting around λ=1.55 μm. The dot is produced using a nanotemplate deposition technique that allows precise a priori control of quantum dot position and electronic configuration. Clear evidence of excitonic shell structure and many-body renormalization effects are observed.

Strained layer InGaAs/GaAs quantum wells have been grown by molecular‐beam epitaxy on patterned (100) GaAs substrates. Indium migration away from the facets of patterned mesas is shown to be strongly dependent upon the arsenic flux during growth. Based upon this effect we have grown structures in which the number of active quantum wells in adjacent areas of a segmented contact device can be varied.

Spatially selective compositional disordering induced by focused Ga+ ion beam implantation in GaAs/AlGaAs and strained InGaAs/GaAs quantum well structures has been studied using photoluminescence. We find that beyond a certain implantation dosage, the degree of intermixing imparted to a given quantum well saturates and may eventually decline as a result of damage to the semiconductor surface. We overcome this limitation by thermally annealing the sample after implantation to repair the crystalline surface. We show that multiple successive implants interspersed with rapid thermal anneals (RTAs) are successful in locally shifting the optical band gap of quantum wells by many times that attributed to a single implant and RTA.

The migration of indium on patterned substrates during MBE growth is found to be strongly dependent upon the arsenic species used. InGaAs-GaAs SQW lasers grown on narrow mesas using AS/sub 4/ exhibited 70-meV redshifts, while those grown using As/sub 2/ showed only small redshifts.

Semiconductor lasers emitting at 1.3 /spl mu/m and 1.55 /spl mu/m wavelengths are of particular interest because of their application in optical fibre communication systems. In this work, we investigate for the first time the process of indium migration during the growth of InGaAs-InAlAs single quantum wells grown by MBE on patterned InP substrates for the fabrication of long wavelength integrated optoelectronic devices.

Although it has been known for many years that GaAs/AlGaAs quantum-well (QW) lasers exhibit low temperature sensitivity, or high characteristic temperatures, T/sub 0/, to our knowledge, optimization of the laser structure so as to maximize T/sub 0/ has never been shown. Previous work in GaAs/AlGaAs has been limited in scope, either only to Al content in the cladding layers and QW thickness, or to a small variety of numbers of quantum wells, n. There has also been work done on the influence of the number of wells in InP-based lasers at 1.3 /spl mu/m and 1.5 /spl mu/m wavelengths. In this paper, we present results of an experimental study on the variation of T/sub 0/ in graded-index, separate-confinement heterostructure GaAs/(Al,Ga)As QW lasers as a function of the Al content in the cladding layers at two different nominal values, and of the number of wells, ranging from n=l to 10.

Selective area chemical beam epitaxy is used to fabricate submicron [100]-oriented InP ridges with well-defined, defect-free (011) sidefacets and (001) tops. Following the deposition of two monolayers of InAs on such nanotemplates and subsequent capping with InP, photoluminescence spectra show for wider ridges strong emission from a thin InAs quantum well and, as the ridge width is reduced, a gradual appearance of a quantum dot emission at lower energy. The method allows continuous tuning on a given sample in a single growth run of both the quantum dot density and the emission wavelength. The result is a consequence of adatom diffusion from the ridge sidefacets onto the top (001) facet, which increases the amount of InAs beyond the critical thickness for three-dimensional nucleation to occur. Compared with growth on planar InP(001) substrates, InAs self-assembled quantum dots grown on these nanotemplates are more uniform as revealed by a twofold reduction in emission linewidth at 4 K.

We have used transmission electron microscopy and low temperature photoluminescence to study the growth by chemical beam epitaxy of self-assembled InAs/InP quantum dots as a function of growth interruption time. As the deposited InAs layer is given time to migrate on the semiconductor surface a number of different features appear. The InAs layer first forms a rough quantum well with monolayer fluctuations in width before forming elongated InAs islands. These islands are elongated along the [01-1] direction due to surface diffusion dynamics. These then break up into individual quantum dots, and slowly increase in height. These dots are found to be approximately square with their sides aligned along the 〈100〉 directions and lateral dimensions of 30–40 nm.