Feeding predictability as a cognitive enrichment protects brain function and physiological status in rainbow trout: a multidisciplinary approach to assess fish welfare

Cognitive enrichment is a promising but understudied type of environmental enrichment that aims to stimulate the cognitive abilities of animals by providing them with more opportunities to interact with (namely, to predict events than can occur) and to control their environment. In a previous study, we highlighted that farmed rainbow trout can predict daily feedings after two weeks of conditioning, the highest conditioned response being elicited by the combination of both temporal and signalled predictability. In the present study, we tested the feeding predictability that elicited the highest conditioned response in rainbow trout (both temporal and signalled by bubbles, BUBBLE + TIME treatment) as a cognitive enrichment strategy to improve their welfare. We thus analysed the long-term effects of this feeding predictability condition as compared with an unpredictable feeding condition (RANDOM treatment) on the welfare of rainbow trout, including the markers in the modulation of brain function, through a multidisciplinary approach. To reveal the brain regulatory pathways and networks involved in the long-term effects of feeding predictability, we measured gene markers of cerebral activity and plasticity, neurotransmitter pathways and physiological status of fish (oxidative stress, inflammatory status, cell type and stress status). After almost three months under these predictability conditions of feeding, we found clear evidence of improved welfare in fish from BUBBLE + TIME treatment. Feeding predictability allowed for a food anticipatory activity and resulted in fewer aggressive behaviours, burst of accelerations, and jumps before mealtime. BUBBLE + TIME fish were also less active between meals, which is in line with the observed decreased expression of transcripts related to the dopaminergic system. BUBBLE + TIME fish tented to present fewer eroded dorsal fin and infections to the pathogen Flavobacterium psychrophilum. Decreased expression of most of the studied mRNA involved in oxidative stress and immune responses confirm these tendencies else suggesting a strong role of feeding predictability on fish health status and that RANDOM fish may have undergone chronic stress. Fish emotional reactivity while isolated in a novel-tank as measured by fear behaviour and plasma cortisol levels were similar between the two treatments, as well as fish weight and size. To conclude, signalled combined with temporal predictability of feeding appears to be a promising approach of cognitive enrichment to protect brain function via the physiological status of farmed rainbow trout in the long term.

Measurement of the ν_{e}-Nucleus Charged-Current Double-Differential Cross Section at ⟨E_{ν}⟩=2.4 GeV Using NOvA

The inclusive electron neutrino charged-current cross section is measured in the NOvA near detector using 8.02×10^{20} protons-on-target in the NuMI beam. The sample of GeV electron neutrino interactions is the largest analyzed to date and is limited by ≃17% systematic rather than the ≃7.4% statistical uncertainties. The double-differential cross section in final-state electron energy and angle is presented for the first time, together with the single-differential dependence on Q^{2} (squared four-momentum transfer) and energy, in the range 1  GeV≤E_{ν}<6  GeV. Detailed comparisons are made to the predictions of the GENIE, GiBUU, NEUT, and NuWro neutrino event generators. The data do not strongly favor a model over the others consistently across all three cross sections measured, though some models have especially good or poor agreement in the single differential cross section vs Q^{2}.

Broadband high-contrast visible optical switches based on a spin-crossover material

Visible optical switches embedding a spin-crossover thin film and exploiting the frustrated total internal reflection operation principle are studied and optimized numerically with a view to obtain broadband high-contrast devices. A practical implementation using uncoated SF11 prisms embedding a 1-µm-thick layer of iron-triazolyl-borate complex as the thermo-active phase-change material is shown to support p-polarized modulation with contrast in excess of 90% over a spectral bandwidth greater than 270 nm and over an angular acceptance bandwidth of 0.45°, surpassing the performance achievable with optically resonant devices.

Scintillation light detection in the 6-m drift-length ProtoDUNE Dual Phase liquid argon TPC

DUNE is a dual-site experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. ProtoDUNE Dual Phase (DP) is a 6  ×  6  ×  6 m 3 liquid argon time-projection-chamber (LArTPC) that recorded cosmic-muon data at the CERN Neutrino Platform in 2019-2020 as a prototype of the DUNE Far Detector. Charged particles propagating through the LArTPC produce ionization and scintillation light. The scintillation light signal in these detectors can provide the trigger for non-beam events. In addition, it adds precise timing capabilities and improves the calorimetry measurements. In ProtoDUNE-DP, scintillation and electroluminescence light produced by cosmic muons in the LArTPC is collected by photomultiplier tubes placed up to 7 m away from the ionizing track. In this paper, the ProtoDUNE-DP photon detection system performance is evaluated with a particular focus on the different wavelength shifters, such as PEN and TPB, and the use of Xe-doped LAr, considering its future use in giant LArTPCs. The scintillation light production and propagation processes are analyzed and a comparison of simulation to data is performed, improving understanding of the liquid argon properties.

Cavity resonator-integrated guided-mode resonance filters with on-chip electro- and thermo-optic tuning

Cavity resonator grating filters (CRIGFs) integrated on lithium niobate on insulator (LNOI) with electrical tuning elements are reported. The resonance wavelength of the filters is in the 780 nm range. Integrated thermo-optical tuning range of 2.5 nm is measured using integrated resistors, whilst a 0.7 nm electro-optical tuning range using capacitive metallic pads is achieved with ±400V drive voltage.

Search for Active-Sterile Antineutrino Mixing Using Neutral-Current Interactions with the NOvA Experiment

This Letter reports results from the first long-baseline search for sterile antineutrinos mixing in an accelerator-based antineutrino-dominated beam. The rate of neutral-current interactions in the two NOvA detectors, at distances of 1 and 810 km from the beam source, is analyzed using an exposure of 12.51×10^{20} protons-on-target from the NuMI beam at Fermilab running in antineutrino mode. A total of 121 of neutral-current candidates are observed at the far detector, compared to a prediction of 122±11(stat.)±15(syst.) assuming mixing only between three active flavors. No evidence for ν[over ¯]_{μ}→ν[over ¯]_{s} oscillation is observed. Interpreting this result within a 3+1 model, constraints are placed on the mixing angles θ_{24}<25° and θ_{34}<32° at the 90% C.L. for 0.05  eV^{2}≤Δm_{41}^{2}≤0.5  eV^{2}, the range of mass splittings that produces no significant oscillations at the near detector. These are the first 3+1 confidence limits set using long-baseline accelerator antineutrinos.

Prospects for beyond the Standard Model physics searches at the Deep Underground Neutrino Experiment: DUNE Collaboration

The Deep Underground Neutrino Experiment (DUNE) will be a powerful tool for a variety of physics topics. The high-intensity proton beams provide a large neutrino flux, sampled by a near detector system consisting of a combination of capable precision detectors, and by the massive far detector system located deep underground. This configuration sets up DUNE as a machine for discovery, as it enables opportunities not only to perform precision neutrino measurements that may uncover deviations from the present three-flavor mixing paradigm, but also to discover new particles and unveil new interactions and symmetries beyond those predicted in the Standard Model (SM). Of the many potential beyond the Standard Model (BSM) topics DUNE will probe, this paper presents a selection of studies quantifying DUNE's sensitivities to sterile neutrino mixing, heavy neutral leptons, non-standard interactions, CPT symmetry violation, Lorentz invariance violation, neutrino trident production, dark matter from both beam induced and cosmogenic sources, baryon number violation, and other new physics topics that complement those at high-energy colliders and significantly extend the present reach.

Focal Areas of High Signal Intensity in Children with Neurofibromatosis Type 1: Expected Evolution on MRI

BACKGROUND AND PURPOSE

Focal areas of high signal intensity are T2WI/T2-FLAIR hyperintensities frequently found on MR imaging of children diagnosed with neurofibromatosis type 1, often thought to regress spontaneously during adolescence or puberty. Due to the risk of tumor in this population, some focal areas of high signal intensity may pose diagnostic problems. The objective of this study was to assess the characteristics and temporal evolution of focal areas of high signal intensity in children with neurofibromatosis type 1 using long-term follow-up with MR imaging.

MATERIALS AND METHODS

We retrospectively examined the MRIs of children diagnosed with neurofibromatosis type 1 using the National Institutes of Health Consensus Criteria (1987), with imaging follow-up of at least 4 years. We recorded the number, size, and surface area of focal areas of high signal intensity according to their anatomic distribution on T2WI/T2-FLAIR sequences. A generalized mixed model was used to analyze the evolution of focal areas of high signal intensity according to age, and separate analyses were performed for girls and boys.

RESULTS

Thirty-nine patients (ie, 285 MR images) with a median follow-up of 7 years were analyzed. Focal areas of high signal intensity were found in 100% of patients, preferentially in the infratentorial white matter (35% cerebellum, 30% brain stem) and in the capsular lenticular region (22%). They measured 15 mm in 95% of cases. They appeared from the age of 1 year; increased in number, size, and surface area to a peak at the age of 7; and then spontaneously regressed by 17 years of age, similarly in girls and boys.

CONCLUSIONS

Focal areas of high signal intensity are mostly small (<15 mm) abnormalities in the posterior fossa or capsular lenticular region. Our results suggest that the evolution of focal areas of high signal intensity is not related to puberty with a peak at the age of 7 years. Knowledge of the predictive evolution of focal areas of high signal intensity is essential in the follow-up of children with neurofibromatosis type 1.

Interband cascade Lasers with AlGaAsSb cladding layers emitting at 3.3 µm

We investigate the impact of the growth conditions of AlGaAsSb cladding layers on the properties of interband cascade lasers (ICLs). For an optimized structure emitting at 3.3 µm, we achieve an internal quantum efficiency of 65% per stage in good agreement with conventional ICL using InAs/AlSb superlattice cladding layers, in spite of internal losses of 15 cm^-1 due to higher optical losses in the n-type AlGaAsSb alloys. Finally, we report a narrow ridge ICL emitting at 3.33 µm operating in continuous wave up to 80°C that produces 1 mW/uncoated facet at 80 °C, 10 mW at 40 °C and more than 12 mW at 20°C.

First measurement of neutrino oscillation parameters using neutrinos and antineutrinos by NOvA

The NOvA experiment has seen a 4.4σ signal of ν[over ¯]_{e} appearance in a 2 GeV ν[over ¯]_{μ} beam at a distance of 810 km. Using 12.33×10^{20} protons on target delivered to the Fermilab NuMI neutrino beamline, the experiment recorded 27 ν[over ¯]_{μ}→ν[over ¯]_{e} candidates with a background of 10.3 and 102 ν[over ¯]_{μ}→ν[over ¯]_{μ} candidates. This new antineutrino data are combined with neutrino data to measure the parameters |Δm_{32}^{2}|=2.48_{-0.06}^{+0.11}×10^{-3}  eV^{2}/c^{4} and sin^{2}θ_{23} in the ranges from (0.53-0.60) and (0.45-0.48) in the normal neutrino mass hierarchy. The data exclude most values near δ_{CP}=π/2 for the inverted mass hierarchy by more than 3σ and favor the normal neutrino mass hierarchy by 1.9σ and θ_{23} values in the upper octant by 1.6σ.

Development of methods for the preparation of radiopure 82Se sources for the SuperNEMO neutrinoless double-beta decay experiment

A radiochemical method for producing 82Se sources with an ultra-low level of contamination of natural radionuclides (40K, decay products of 232Th and 238U) has been developed based on cation-exchange chromatographic purification with reverse removal of impurities. It includes chromatographic separation (purification), reduction, conditioning (which includes decantation, centrifugation, washing, grinding, and drying), and 82Se foil production. The conditioning stage, during which highly dispersed elemental selenium is obtained by the reduction of purified selenious acid (H2SeO3) with sulfur dioxide (SO2) represents the crucial step in the preparation of radiopure 82Se samples. The natural selenium (600 g) was first produced in this procedure in order to refine the method. The technique developed was then used to produce 2.5 kg of radiopure enriched selenium (82Se). The produced 82Se samples were wrapped in polyethylene (12 μm thick) and radionuclides present in the sample were analyzed with the BiPo-3 detector. The radiopurity of the plastic materials (chromatographic column material and polypropylene chemical vessels), which were used at all stages, was determined by instrumental neutron activation analysis. The radiopurity of the 82Se foils was checked by measurements with the BiPo-3 spectrometer, which confirmed the high purity of the final product. The measured contamination level for 208Tl was 8–54 μBq/kg, and for 214Bi the detection limit of 600 μBq/kg has been reached.

Low-loss buried AlGaAs/AlOx waveguides using a quasi-planar process

In this paper, we demonstrate that buried oxide-confined waveguides can be formed using a lateral oxidation process carried out through a discrete set of small-diameter via-holes instead of the conventional scheme where the oxidation starts from the edges of etched mesas. The via-hole oxidation is shown to lead to straight waveguides with smooth oxide/semiconductor interfaces and whose propagation losses are similar to one obtained using the standard process but with the advantage of maintaining a quasi-planar wafer surface. It thereby paves the way towards a simplification of the fabrication of III-V-semiconductor-oxide photonic devices.

Search for Neutrinoless Quadruple-β Decay of ^{150}Nd with the NEMO-3 Detector

We report the results of a first experimental search for lepton number violation by four units in the neutrinoless quadruple-β decay of ^{150}Nd using a total exposure of 0.19 kg yr recorded with the NEMO-3 detector at the Modane Underground Laboratory. We find no evidence of this decay and set lower limits on the half-life in the range T_{1/2}>(1.1-3.2)×10^{21}  yr at the 90% C.L., depending on the model used for the kinematic distributions of the emitted electrons.

The BiPo-3 detector

The BiPo-3 detector is a low radioactive detector dedicated to measuring ultra-low natural contaminations of ²⁰⁸Tl and ²¹⁴Bi in thin materials, initially developed to measure the radiopurity of the double β decay source foils of the SuperNEMO experiment at the μBq/kg level. The BiPo-3 technique consists in installing the foil of interest between two thin ultra-radiopure scintillators coupled to low radioactive photomultipliers. The design and performances of the detector are presented. In this paper, the final results of the ²⁰⁸Tl and ²¹⁴Bi activity measurements of the first enriched ⁸²Se foils are reported for the first time, showing the capability of the detector to reach sensitivities in the range of some μBq/kg.

Physiological and Structural Differences Between Enterococcus faecalis JH2-2 and Mutant Strains Resistant to (P)-Divercin RV41

The aim of this study was to show the differences that could exist at the physiological and structural levels between Enterococcus faecalis JH2-2 (wild type) and three mutant strains resistant to divercin RV41. These mutant strains were recently isolated and characterized for their intermediate resistance to recombinant DvnRV41; a subclass IIa bacteriocin produced by Escherichia coli. These mutant strains were named 35A1 (altered in gene coding phosphoesterase activity), 35H1 (altered in gene coding σ(54) factor) and 36H4 (altered in gene coding glycerophosphodiesterase). The growth and resistance of each strain were tested against lysozyme. The inhibitory substance did not show any cross-resistance but exhibited an additive effect ascribed to the combined action of lysozyme and (P)-DvnRV41. The use of Fourier transform infrared spectroscopy (FT-IR) allowed to unravelling differences at the structural levels between the aforementioned strains. Thus, mutants 35H1 and 36H4 showed clear differences from mutant 35A1 and wild-type strain. These differences were located, mainly in the fatty acid region and in the polysaccharide composition. This study contributes to understanding more the resistance/sensitivity of Ent. faecalis to (P)-DvnRV41, a subclass IIa bacteriocin.

Electrically-controlled rapid femtosecond pulse duration switching and continuous picosecond pulse duration tuning in an ultrafast Cr4+:forsterite laser

We demonstrate rapid switching between picosecond and femtosecond operational regimes in a Cr(4+):forsterite laser, using an electrically-contacted GaInNAs SESAM with saturable absorption characteristics controlled via the quantum-confined Stark effect. Additionally, continuous picosecond pulse duration tuning by over a factor 3 is reported.

Genetic diversity of Flavobacterium psychrophilum isolated from rainbow trout in France: predominance of a clonal complex

Flavobacterium psychrophilum is the causative agent of "bacterial cold water disease" and "rainbow trout fry syndrome" in salmonid farming worldwide. These diseases, especially rainbow trout fry syndrome, are among the main hazards for French aquaculture. In this study, a multilocus sequence typing approach (MLST) was used to evaluate the genetic diversity of this bacterium. Seven housekeeping genes in a set of 66 isolates were investigated. They were recently collected from rainbow trout during clinical episodes in French farms from the two main geographical areas of production. A total of 5808 bp of sequence were analyzed for each isolate and showed relatively low levels of gene (H=0.4313) and nucleotide (π×100=0.31%) diversities. MLST identified 15 sequence types (STs), of which 14 have never been described. eBURST analysis separated the 15 STs in one clonal complex of 8 genetically related STs (with ST2 as founder) and 7 singletons. Genetic diversity was largely due to recombination, as demonstrated by a pairwise homoplasy index (PHI=5.35×10(-9)) significantly different from zero (p<0.05). The evolution of standardized association index (I(A)(S)) (all isolates: 0.6088, p<0.05; single representative of STs: 0.4567, p<0.05; and clusters of STs: 0.084, p>0.05), showed an epidemic structure of the population. These results emphasized the expansion of a limited number of dominant genetic variants in French clinical F. psychrophilum isolates from a single host species, with no geographic relationships.

Optical trapping with "on-demand" two-photon luminescence using Cr:LiSAF laser with optically addressed saturable Bragg reflector

We demonstrate a diode-pumped Cr:LiSAF laser with controllable and reliable fast switching between its continuous-wave and mode-locked states of operation using an optically-addressed semiconductor Bragg reflector, permitting dyed microspheres to be continuously trapped and monitored using a standard microscope imaging and on-demand two-photon-excited luminescence techniques.

Broadly tunable femtosecond mode-locking in a Tm:KYW laser near 2 μm

Efficient mode-locking in a Tm:KY(WO(4))(2) laser is demonstrated by using InGaAsSb quantum-well SESAMs. Self-starting ultrashort pulse generation was realized in the 1979-2074 nm spectral region. Maximum average output power up to 411 mW was produced around 1986 nm with the corresponding pulse duration and repetition rate of 549 fs and 105 MHz respectively. Optimised pulse durations of 386 fs were produced with an average power of 235 mW at 2029 nm.

Femtosecond mode-locked Tm(3+) and Tm(3+)-Ho(3+) doped 2 μm glass lasers

We report on the spectroscopic characterization, continuous-wave and continuous wave mode-locked laser performance of bulk Tm(3+):GPNG fluorogermanate and Tm(3+)-Ho(3+):TZN tellurite glass lasers around 2 μm. A slope efficiency of up to 50% and 190 mW of output power were achieved from the Tm(3+):GPNG laser at 1944 nm during continuous wave operation. The Tm(3+)-Ho(3+):TZN laser produced a 26% slope efficiency with a maximum output power of 74 mW at 2012 nm. The Tm(3+):GPNG produced near-transform-limited pulses of 410 fs duration centered at 1997 nm with up to 84 mW of average output power and repetition frequency of 222 MHz when was passively modelocked using an ion-implanted InGaAsSb-based quantum well SESAM. Using the same SESAM, the Tm(3+)-Ho(3+):TZN laser generated 630-fs pulses with 38 mW of average output power at 2012 nm. Data analysis of pulses at different intracavity pulse energies provided an estimation of n(2) at 2012 nm of 2.9 × 10(-15) cm(2)/W for the Tm(3+)-Ho(3+):TZN.

Femtosecond (191 fs) NaY(WO4)2 Tm,Ho-codoped laser at 2060 nm

We report, for the first time to our knowledge, femtosecond-pulse operation of a Tm,Ho:NaY(WO(4))(2) laser at around 2060 nm. Transform-limited 191 fs pulses are produced with an average output power of 82 mW at a 144 MHz pulse repetition frequency. Maximum output power of up to 155 mW is generated with a corresponding pulse duration of 258 fs. An ion-implanted InGaAsSb quantum-well-based semiconductor saturable absorber mirror is used for passive mode-locking maintenance.

Cavity-dumping of a semiconductor disk laser for the generation of wavelength-tunable micro-Joule nanosecond pulses

We report on cavity-dumping of a semiconductor disk laser as a method to generate energetic wavelength-tunable nanosecond pulses with repetition rates ranging from 0.1 to 4 MHz. Experimentally, emission of 24 ns pulses with peak output power of 41 W in a single beam output (and of 30 ns with peak power of 57 W in a combined beam output) with wavelength tuning from 1045 to 1080 nm was obtained. Numerical modeling is also introduced to provide more insight into the most important parameters controlling this mode of operation and to define optimization avenues.

Femtosecond pulse operation of a Tm,Ho-codoped crystalline laser near 2 microm

We demonstrate, for the first time to our knowledge, femtosecond-regime mode locking of a Tm,Ho-codoped crystalline laser operating in the 2 microm spectral region. Transform-limited 570 fs pulses were generated at 2055 nm by a Tm,Ho:KY(WO(4))(2) laser that produced an average output power of 130 mW at a pulse repetition frequency of 118 MHz. Mode locking was achieved using an ion-implanted InGaAsSb quantum-well-based semiconductor saturable absorber mirror.

Thermal lens study in diode pumped Ng- and Np-cut Nd:KGd(WO4)2 laser crystals

A comparative study of thermal lensing effect in diode laser pumped Ng- and Np-cut Nd:KGd(WO4)2 (KGW) laser crystals was performed for laser emission polarized along the principle refractive axis, Nm. The thermal lens in the Ng-cut Nd: KGW was found to be weakly astigmatic with a positive refractive power for both the Nm- and Np-directions. For Np -cut Nd:KGW, strong astigmatism was observed and the refractive powers in the Ng- and Nm-directions had opposing signs. The degree of astigmatism was found to be considerably weaker for the Ng-cut Nd:KGW in comparison with the Np-cut one: 0.35 dptr/(W/cm2) and 2.85 dptr/(W/cm2), respectively. The ratio of the thermal lens refractive powers in the planes parallel and perpendicular to the laser emission polarisation were measured as +1.4 and -0.425 for Ng- and Np-cut Nd:KGW respectively.

InP/AlGaInP quantum dot semiconductor disk lasers for CW TEM00 emission at 716 - 755 nm

Multiple layers of InP QDs, self-assembled during epitaxial growth, were incorporated into the active region of an (Al(x)Ga(1-x))(0.51)In(0.49)P based semiconductor disk laser with monolithic Al(x)Ga(1-x)As distributed Bragg reflector. Three gain structure samples were selected from the epitaxial wafer, bonded to single-crystal diamond heatspreaders and optically pumped at 532 nm within a high finesse external laser cavity. Laser emission with peak wavelengths at 716, 729, and 739 nm, respectively, was achieved from the three samples; the latter demonstrating tuning from 729 to 755 nm. Maximum continuous wave output power of 52 mW at 739 nm was achieved with 0.2% output coupling; the threshold and slope efficiency were 220 mW and 5.7% respectively.

Passive mode locking of a Tm,Ho:KY(WO4)2 laser around 2 microm

We report the first demonstration, to our knowledge, of passive mode locking in a Tm(3+), Ho(3+)-codoped KY(WO(4))(2) laser operating in the 2000-2060 nm spectral region. An InGaAsSb-based quantum well semiconductor saturable absorber mirror is used for the initiation and stabilization of the ultrashort pulse generation. Pulses as short as 3.3 ps were generated at 2057 nm with average output powers up to 315 mW at a pulse repetition frequency of 132 MHz for 1.15 W of absorbed pump power at 802 nm from a Ti:sapphire laser.

Optically-pumped saturable absorber for fast switching between continuous-wave and passively mode-locked regimes of a Nd:YVO4 laser

We report on the fast (approximately 50 micros) remote-controlled switching between continuous-wave (cw), cw mode-locked (ML) and Q-switched ML modes of operation of a Nd:YVO(4) laser using an optically-pumped saturable absorber (SA). Pulses as short as 40 ps with an average output power of 0.5 W are obtained in cw ML regime.

Femtosecond pulse generation around 1500 nm using a GaInNAsSb SESAM

The operation of a femtosecond Cr(4+):YAG laser that incorporates a novel GaInNAsSb semiconductor saturable Bragg reflector is reported. In the mode-locked regime 230 fs pulses centred at 1528 nm were generated at an average output power of 280 mW. The SESAM exhibited a low saturation fluence of 10 microJ/cm(2) and a short recovery time of 12 ps.

Stabilization of a semiconductor disk laser using an intra-cavity high reflectivity grating

We demonstrate the use of a High Reflectivity Grating (HRG) as an intra-cavity element in a Semiconductor Disk Laser (or Vertical External Cavity Surface Emitting Laser) to stabilise its emission wavelength and polarization characteristics. Operation at 1058nm with up to 645mW of pump-limited output power and an M(2)~1.4 is achieved. We also show that this scheme permits tunable single-frequency operation.

Tunable single-mode fiber-VCSEL using an intracavity polymer microlens

We report a tunable, single-mode vertical cavity surface-emitting laser (VCSEL) format suitable for array operation, power scaling, fiber coupling, and operation in isolated environments such as those required by atom optics. The devices are fiber VCSELs, consisting of a semiconductor gain and mirror structure separated from a mirror-coated optical fiber by an air (or vacuum) gap. The gain structure has polymer microlenses fabricated on its surface, of characteristics suitable to focus the oscillating mode on both cavity mirrors, ensuring stable fundamental mode emission and high fiber coupling efficiency. We demonstrate such devices in continuous-wave operation at 1.03 microm at room temperature, with a single-mode tuning range of 13 nm, laser threshold as low as 2.5 mW, and a maximum fiber-coupled output power of 10 mW.

Microlensed microchip VECSEL

We report a 1.055-mum microchip VECSEL array which uses a microlens-patterned diamond both as a heatspreader and as an array of concave output mirrors. This configuration, which is suitable for laser array operation, is here exploited to perform a systematic study of a set of microchip lasers with the same semiconductor structure but different cavity properties. The transverse mode selection of individual VECSELs is found to depend on the mode-matching conditions and on the microlens aperture size. Mode-matched single-device emission in the fundamental mode (M2~1.1) with pump-limited output power of 70 mW is demonstrated.

Improvement of enterocin P purification process

Purification and heterologous expression of enterocin P (EntP), a sec-dependent bacteriocin produced by Enterococcus faecium, in Escherichia coli is described. PCR-amplified product of the enterocin P structural gene entP was cloned into plasmid pET-32b under the control of the inducible T7lac promoter. The neo-synthesized EntP was genetically modified by an addition of 3 extra amino acids, leading to recombinant EntRP. Active EntRP was recovered from the cytoplasmic soluble fraction of E. coli harboring appropriate recombinant plasmid, characterized by ELISA and Western-blot analysis and purified by immunoaffinity chromatography. The use of E. coli as heterologous host and pET-32b as expressing vector offers promising tools for heterologous production of class IIa bacteriocin.

Intracavity diamond heatspreaders in lasers: the effects of birefringence

The birefringence of a number of commercially-available diamond platelets is assessed in the context of their use for intracavity thermal management in lasers. Although diamond is normally thought of as isotropic, significant birefringence is found to be present in some samples, with considerable variation from batch to batch, and in some cases across an individual sample. Nonetheless, low-loss operation is achieved in a laser cavity containing a Brewster element, either by rotating the sample or by using a diamond platelet with low birefringence.

Slow-light in a vertical-cavity semiconductor optical amplifier

This paper discusses the effect of slow-light in Vertical-Cavity Semiconductor Optical Amplifiers. A Fabry-Perot model is used to predict the group delay (GD) and GD-bandwidth performance of a VCSOA operated in reflection in the linear regime. It is shown that the GD depends on all cavity parameters while the GDxGD-bandwidth product only depends on the gain. Experimental demonstration with a 1300nm GaInNAs VCSOA is used to validate the model and demonstrate tunable GDs between 25 and 100 ps by varying the VCSOA gain. Experimental distortion of the signals induced by nonlinear effects is also presented.

Red microchip VECSEL array

We report an InGaP/AlInGaP/GaAs microchip vertical-external-cavity surface emitting laser operating directly at red wavelengths and demonstrate its potential for array-format operation. Optical pumping with up to 3.3W at 532nm produced a maximum output power of 330mW at 675nm, in a single circularly-symmetric beam with M2<2. Simultaneous pumping with three separate input beams, generated using a diffractive optical element, achieved lasing from three discrete areas of the same chip. Output power of ~95mW per beam was obtained from this 3x1 array, each beam having a Gaussian intensity profile with M2<1.2. In a further development, a spatial light modulator allowed computer control over the orientation and separation of the pump beams, and hence dynamic control over the configuration of the VECSEL array.

High power CW red VECSEL with linearly polarized TEM00 output beam

High-power, continuous-wave operation at red wavelengths has been achieved with a vertical external cavity surface emitting laser based on the GaInP/AlGaInP/GaAs material system. Output power of 0.4W was obtained in a linearly polarized, circularly symmetric, diffraction-limited beam. A birefringent filter inserted in the cavity allowed tuning of the laser output spectrum over a 10nm range around 674nm.

Low-loss 1.3-microm GaInNAs saturable Bragg reflector for high-power picosecond neodymium lasers

A novel low-loss, single-step-growth 1.3-microm GaInNAs saturable Bragg reflector mode-locking element has been developed. Combined radial thickness and postgrowth annealing control have permitted a tuning range of 46 nm for passive mode locking to be demonstrated from one wafer. With this structure, stabilized mode locking was obtained from quasi-cw diode-pumped Nd:YLF and Nd:YALO lasers operating at 1314 and 1342 nm, respectively, with average on-time output powers of as much as 20 W and pulse durations as low as 22 ps.