Q-switched Dy:ZBLAN fiber lasers beyond 3 µm: comparison of pulse generation using acousto-optic modulation and inkjet-printed black phosphorus.

We report high-energy mid-infrared pulse generation by Q-switching of dysprosium-doped fiber lasers for the first time. Two different modulation techniques are demonstrated. Firstly, using active acousto-optic modulation, pulses are produced with up to 12 µJ energy and durations as short as 270 ns, with variable repetition rates from 100 Hz to 20 kHz and central wavelengths tunable from 2.97 to 3.23 µm. Experiments are supported by numerical modeling, identifying routes for improved pulse energies and to avoid multi-pulsing by careful choice of modulator parameters. Secondly, we demonstrate passive Q-switching by fabricating an inkjet-printed black phosphorus saturable absorber, simplifying the cavity and generating 1.0 µJ pulses with 740 ns duration. The performance and relative merits of each modulation approach are then critically discussed. These demonstrations highlight the potential of dysprosium as a versatile gain medium for high-performance pulsed sources beyond 3 µm.

Watt-level dysprosium fiber laser at 3.15 µm with 73% slope efficiency.

Rare-earth-doped fiber lasers are emerging as promising high-power mid-infrared sources for the 2.6-3.0 µm and 3.3-3.8 µm regions based on erbium and holmium ions. The intermediate wavelength range, however, remains vastly underserved, despite prospects for important manufacturing and defense applications. Here, we demonstrate the potential of dysprosium-doped fiber to solve this problem, with a simple in-band pumped grating-stabilized linear cavity generating up to 1.06 W at 3.15 µm. A slope efficiency of 73% with respect to launched power (77% relative to absorbed power) is achieved-the highest value for any mid-infrared fiber laser to date, to the best of our knowledge. Opportunities for further power and efficiency scaling are also discussed.

Genetic algorithm-based control of birefringent filtering for self-tuning, self-pulsing fiber lasers.

Polarization-based filtering in fiber lasers is well-known to enable spectral tunability and a wide range of dynamical operating states. This effect is rarely exploited in practical systems, however, because optimization of cavity parameters is nontrivial and evolves due to environmental sensitivity. Here, we report a genetic algorithm-based approach, utilizing electronic control of the cavity transfer function, to autonomously achieve broad wavelength tuning and the generation of Q-switched pulses with variable repetition rate and duration. The practicalities and limitations of simultaneous spectral and temporal self-tuning from a simple fiber laser are discussed, paving the way to on-demand laser properties through algorithmic control and machine learning schemes.

Generation of 70-fs pulses at 2.86 µm from a mid-infrared fiber laser.

We propose and demonstrate a simple route to few-optical-cycle pulse generation from a mid-infrared fiber laser through nonlinear compression of pulses from a holmium-doped fiber oscillator using a short length of chalcogenide fiber and a grating pair. Pulses from the oscillator with 265-fs duration at 2.86 µm are spectrally broadened through self-phase modulation in step-index As2S3 fiber to 141-nm bandwidth and then re-compressed to 70 fs (7.3 optical cycles). These are the shortest pulses from a mid-infrared fiber system to date, and we note that our system is compact, robust, and uses only commercially available components. The scalability of this approach is also discussed, supported by numerical modeling.

Wideband saturable absorption in few-layer molybdenum diselenide (MoSe2) for Q-switching Yb-, Er- and Tm-doped fiber lasers.

We fabricate a free-standing molybdenum diselenide (MoSe2) saturable absorber by embedding liquid-phase exfoliated few-layer MoSe2 flakes into a polymer film. The MoSe2-polymer composite is used to Q-switch fiber lasers based on ytterbium (Yb), erbium (Er) and thulium (Tm) gain fiber, producing trains of microsecond-duration pulses with kilohertz repetition rates at 1060 nm, 1566 nm and 1924 nm, respectively. Such operating wavelengths correspond to sub-bandgap saturable absorption in MoSe2, which is explained in the context of edge-states, building upon studies of other semiconducting transition metal dichalcogenide (TMD)-based saturable absorbers. Our work adds few-layer MoSe2 to the growing catalog of TMDs with remarkable optical properties, which offer new opportunities for photonic devices.

Fiber grating compression of giant-chirped nanosecond pulses from an ultra-long nanotube mode-locked fiber laser.

We demonstrate that the giant chirp of coherent, nanosecond pulses generated in an 846 m long, all-normal dispersion, nanotube mode-locked fiber laser can be compensated using a chirped fiber Bragg grating compressor. Linear compression to 11 ps is reported, corresponding to an extreme compression factor of ∼100. Experimental results are supported by numerical modeling, which is also used to probe the limits of this technique. Our results unequivocally conclude that ultra-long cavity fiber lasers can support stable dissipative soliton attractors and highlight the design simplicity for pulse-energy scaling through cavity elongation.

Graphene-based passively mode-locked bidirectional fiber ring laser.

We present an all-fiber bidirectional passively mode-locked soliton laser with a graphene-based saturable absorber for the first time to the best of our knowledge. Our design includes a four-port circulator to introduce different sections of cavity for the two counter-propagating pulses, so they have distinct output characteristics. Simultaneous bidirectional operation is achieved by appropriately adjusting the net cavity birefringence and loss. In the clockwise direction, the laser emits ~750 fs pulses at 1561.6 nm, with a repetition rate of 7.68 MHz. In the counter clockwise direction, the central wavelength, pulse width, and repetition rate are 1561.0 nm, ~850 fs, and 6.90 MHz, respectively.

Tunable Q-switched fiber laser based on saturable edge-state absorption in few-layer molybdenum disulfide (MoS2).

We fabricate a few-layer molybdenum disulfide (MoS2) polymer composite saturable absorber by liquid-phase exfoliation, and use this to passively Q-switch an ytterbium-doped fiber laser, tunable from 1030 to 1070 nm. Self-starting Q-switching generates 2.88 µs pulses at 74 kHz repetition rate, with over 100 nJ pulse energy. We propose a mechanism, based on edge states within the bandgap, responsible for the wideband nonlinear optical absorption exhibited by our few-layer MoS2 sample, despite operating at photon energies lower than the material bandgap.

Fiber-integrated 780 nm source for visible parametric generation.

We report the development of a fully fiber-integrated pulsed master oscillator power fibre amplifier (MOPFA) source at 780 nm, producing 3.5 W of average power with 410 ps pulses at a repetition rate of 50 MHz. The source consists of an intensity modulated 1560 nm laser diode amplified in an erbium fiber amplifier chain, followed by a fiber coupled periodically poled lithium niobate crystal module for frequency doubling. The source is then used for generating visible light through four-wave mixing in a length of highly nonlinear photonic crystal fiber: 105 mW at 668 nm and 95 mW at 662 nm are obtained, with pump to anti-Stokes conversion slope efficiencies exceeding 6% in both cases.

Stimulated Brillouin scattering of visible light in small-core photonic crystal fibers.

We characterize stimulated Brillouin scattering (SBS) of visible light in small-core photonic crystal fiber (PCF). Threshold powers under 532 nm excitation agree with established theory, in contrast to measured values up to five times greater than expected for Brillouin scattering of 1550 nm light. An isolated, single-peaked signal at a Stokes shift of 33.5 GHz is observed, distinct from the multi-peaked Stokes spectra expected when small-core PCF is pumped in the infrared. This wavelength-dependence of the Brillouin threshold, and the corresponding spectrum, are explained by the acousto-optic interactions in the fiber, governed by dimensionless length scales that relate the modal area to the core size, and the pump wavelength to PCF hole pitch. Our results suggest new opportunities for exploiting SBS of visible light in small-core PCFs.

The treatment of haematemesis and upper gastrointestinal bleeding in United Kingdom Armed Forces and other deployed units.

INTRODUCTION: Upper Gastro-intestinal (UGI) bleeding is a significant cause of morbidity worldwide. United Kingdom Armed Forces (UKAFs) are not immune to this condition. There is a substantial body of conflicting evidence regarding initial management and risk stratification. AIM: To provide the background knowledge and treatment pathways required to assess and manage a patient adequately during the first 24 hours of an episode of UGI bleeding. ASSESSMENT: Clinical grading of hypovolaemic shock is inaccurate, but is a broad indicator of severity; the Rockall Score must not be used to assess requirement for intervention. Where laboratory assets are available, the Blatchford score is adequate to assess requirements for intervention. MANAGEMENT: The principles of hypotensive resuscitation (target systolic blood pressure 90 mmHg for the first hour) hold true for UGI bleeds. In areas where endoscopy is available within four hours, a restrictive pattern of packed Red Blood Cell (pRBC) transfusion may be beneficial. Despite limited evidence of benefit, Proton Pump Inhibitors (PPIs) should be given routinely in UKAFs. Where available, in cases of variceal and non-variceal UGI Haemorrhage without locally available endoscopy, administration of tranexamic acid and somatostatin or octreotide should be considered.

The Lucy Thermal Emission Spectrometer (L'TES) Instrument.

The Lucy Thermal Emission Spectrometer (L'TES) will provide remote measurements of the thermophysical properties of the Trojan asteroids studied by the Lucy mission. L'TES is build-to-print hardware copy of the OTES instrument flown on OSIRIS-REx. It is a Fourier Transform spectrometer covering the spectral range 5.71-100 µm (1750-100 cm-1) with spectral sampling intervals of 8.64, 17.3, and 34.6 cm-1 and a 7.3-mrad field of view. The L'TES telescope is a 15.2-cm diameter Cassegrain telescope that feeds a flat-plate Michelson moving mirror mounted on a linear voice-coil motor assembly to a single uncooled deuterated l-alanine doped triglycine sulfate (DLATGS) pyroelectric detector. A significant firmware change from OTES is the ability to acquire interferograms of different length and spectral resolution with acquisition times of 0.5, 1, and 2 seconds. A single ∼0.851 µm laser diode is used in a metrology interferometer to provide precise moving mirror control and IR sampling at 772 Hz. The beamsplitter is a 38-mm diameter, 1-mm thick chemical vapor deposited diamond with an antireflection microstructure to minimize surface reflection. An internal calibration cone blackbody target, together with observations of space, provides radiometric calibration. The radiometric precision in a single spectrum is ≤2.2 × 10-8 W cm-2 sr-1 /cm-1 between 300 and 1350 cm-1. The absolute temperature error is <2 K for scene temperatures >75 K. The overall L'TES envelope size is 37.6 × 29.0 × 30.4 cm, and the mass is 6.47 kg. The power consumption is 12.6 W average. L'TES was developed by Arizona State University with AZ Space Technologies developing the electronics. L'TES was integrated, tested, and radiometrically calibrated on the Arizona State University campus in Tempe, AZ. Initial data from space have verified the instrument's radiometric and spatial performance.

W R Gowers 1895: two unpublished post-graduate lectures.

On 10 May 1893, William Gowers began a series of weekly clinical demonstrations at the National Hospital for the Relief and Cure of the Paralysed and Epileptic at Queen Square, London. The contents of some of these demonstrations were published as 'Post-graduate Clinical Lectures' in the Clinical Journal, and in other learned periodicals. Some were also later included in his book Clinical Lectures on Diseases of the Nervous System. Recently, the manuscripts of what appear to be verbatim transcripts of two further but unpublished demonstrations from Gowers' course in 1895 came to light, one containing alterations made in Gowers' handwriting. The first concerned a case of disseminated sclerosis and its differentiation from hysterical paraplegia, the second transverse myelitis and its consequences for bladder function. Why these lectures were never published remains uncertain, but their relatively unedited contents reveal something of the neurological knowledge, diagnostic reasoning, clinical examination and teaching methods employed by one of the great pioneers of clinical neurology.

Quality-adjusted life years in cancer: pros, cons, and alternatives.

High and rising cancer treatment costs have forced a discussion about the use of cost-effectiveness analyses and other approaches to assess the value of cancer care. Oncologists have traditionally resisted using economic considerations in day-to-day medical considerations, though unavoidably their decisions have important resource implications, and increasingly economic realities are impacting their actions. In this paper, we summarise the use of the quality-adjusted life years to assess the value of cancer care and suggest potential ways to improve upon value measurement in cancer coverage and reimbursement decisions.

The Impact of Medicare's lifetime immunosuppression coverage on racial disparities in kidney graft survival.

Beginning January 1, 2000, Medicare effectively extended its coverage of immunosuppression medications from 3 years to lifetime for patients eligible for Medicare on the basis of age or disability status. We examined the impact of this policy on racial disparities in kidney transplant outcomes at 5 years. Using data from the US Renal Data System, we identified cohorts of Medicare-insured kidney transplant recipients according to patient characteristics defining eligibility for lifetime immunosuppression coverage according to the year 2000 policy. We compared racial disparities in graft survival among those eligible for lifetime coverage with the Kaplan-Meier method. We modeled adjusted associations of patient race, patient income, benefits eligibility category and policy exposure with graft loss by multivariable Cox's regression. The racial disparity in graft survival between African American and non-African American among transplant recipients eligible for the lifetime benefit persisted. The graft survival disparity between high- and low-income African American recipients was insignificantly reduced among those eligible for the lifetime benefit. The results of the study suggest that insurance coverage of medication did not eliminate or reduce the racial disparity in graft survival.

A Systems Approach to Remediating Human Exposure to Arsenic and Fluoride From Overexploited Aquifers.

In semiarid agricultural regions, aquifers have watered widespread economic development. Falling water tables, however, drive up energy costs and can make the water toxic for human consumption. The study area is located in central Mexico, where arsenic and fluoride are widely present at toxic concentrations in well water. We simulated the holistic outcomes from three pumping scenarios over 100 years (2020-2120); (S1) pumping rates increase at a similar rate to the past 40 years, (S2) remain constant, or (S3) decrease. Under scenario S1, by 2120, the depth to water table increased to 426 m and energy consumption for irrigation increased to 4 × 109 kWh/yr. Arsenic and fluoride concentrations increased from 14 to 46 µg/L and 1.0 to 3.6 mg/L, respectively. The combined estimated IQ point decrements from drinking untreated well water lowered expected incomes in 2120 by 27% compared to what they would be with negligible exposure levels. We calculated the 100-year Net Present Value (NPV) of each scenario assuming the 2020 average crop value to water footprint ratio of 0.12 USD/m3. Without drinking water mitigation, S1 and S3 yielded relative NPVs of -5.96 × 109 and 1.51 × 109 USD, respectively, compared to the base case (S2). The relative NPV of providing blanket reverse osmosis treatment, while keeping pumping constant (S2), was 11.55 × 109 USD and this gain increased when combined with decreased pumping (S3). If a high value, low water footprint crop was substituted (broccoli, 1.51 USD/m3), the net gains from increasing pumping were similar in size to those of implementing blanket drinking water treatment.

Viremia control following antiretroviral treatment and therapeutic immunization during primary SIV251 infection of macaques.

Prolonged antiretroviral therapy (ART) is not likely to eradicate human immunodeficiency virus type I (HIV-I) infection. Here we explore the effect of therapeutic immunization in the context of ART during primary infection using the simian immunodeficiency virus (SIV251) macaque model. Vaccination of rhesus macaques with the highly attenuated poxvirus-based NYVAC-SIV vaccine expressing structural genes elicited vigorous virus-specific CD4 + and CD8+ T cell responses in macaques that responded effectively to ART. Following discontinuation of a six-month ART regimen, viral rebound occurred in most animals, but was transient in six of eight vaccinated animals. Viral rebound was also transient in four of seven mock-vaccinated control animals. These data establish the importance of antiretroviral treatment during primary infection and demonstrate that virus-specific immune responses in the infected host can be expanded by therapeutic immunization.

Mucosal AIDS vaccine reduces disease and viral load in gut reservoir and blood after mucosal infection of macaques.

Given the mucosal transmission of HIV-1, we compared whether a mucosal vaccine could induce mucosal cytotoxic T lymphocytes (CTLs) and protect rhesus macaques against mucosal infection with simian/human immunodeficiency virus (SHIV) more effectively than the same vaccine given subcutaneously. Here we show that mucosal CTLs specific for simian immunodeficiency virus can be induced by intrarectal immunization of macaques with a synthetic-peptide vaccine incorporating the LT(R192G) adjuvant. This response correlated with the level of T-helper response. After intrarectal challenge with pathogenic SHIV-Ku2, viral titers were eliminated more completely (to undetectable levels) both in blood and intestine, a major reservoir for virus replication, in intrarectally immunized animals than in subcutaneously immunized or control macaques. Moreover, CD4+ T cells were better preserved. Thus, induction of CTLs in the intestinal mucosa, a key site of virus replication, with a mucosal AIDS vaccine ameliorates infection by SHIV in non-human primates.

Association of marital status with access to renal transplantation.

In this report we evaluated the association of marital status with access to renal transplantation. We analyzed data from the USRDS. In patients with ESRD aged ≥ 27 (mean age of first marriage in the US), we analyzed the association of marital status with two outcomes: (1) likelihood of being placed on the waiting list for renal transplantation or first transplant, (2) likelihood of receiving kidney transplant in patients already listed. We analyzed marital status as a categorical variable: (1) not married (including never been married and widowed); (2) divorced or separated; and (3) currently married. Subgroups based on age, race, sex, donor type and diabetic status were also analyzed. After adjustments for the included independent variables and compared to individuals never married or widowed, those who were divorced/separated (HR 1.55, p < 0.001) and currently married (HR 1.54, p < 0.001) had a higher likelihood of being placed on the transplant waiting list. Once listed, married individuals had higher chances of getting transplanted as well (HR 1.28, p = 0.033). This trend was consistent in most of the subgroups studied. We demonstrated that being married is associated with better access to renal transplantation compared to those who were never married/widowed.

Far-ultraviolet imaging spectroscopy of Io's atmosphere with HST/STIS.

Well-resolved far-ultraviolet spectroscopic images of O I, S I, and previously undetected H ILyman-alpha emission from Io were obtained with the Hubble space telescope imaging spectrograph (STIS). Detected O I and S I lines (1250 to 1500 angstroms) have bright equatorial spots (up to 2.5 kilorayleighs) that shift position with jovian magnetic field orientation; limb glow that is brighter on the hemisphere facing the jovian magnetic equator; and faint diffuse emission extending to approximately 20 Io radii. All O I and S I features brightened by approximately 50 percent in the last two images, concurrently with a ground-based observation of increased iogenic [O I] 6300-angstrom emission. The H ILyman-alpha emission, consisting of a small, approximately 2-kilorayleigh patch near each pole, has a different morphology and time variation.