Parasitic Suppression Research Articles

A 1150-W 1018-nm Fiber Laser Bidirectional Pumped by Wavelength-Stabilized Laser Diodes

This paper presented a high-power 1018-nm ytterbium-doped fiber laser pumped by wavelength-stabilized laser diodes in bidirectional pumping structure. A record output power reaching 1150 W was achieved, along with a slope efficiency of 82.9% and a beam quality factor of M2 = 1.96. The output spectrum exhibited an efficient amplified spontaneous emission and parasitic lasing light suppression. The thermal effects were studied to verify the reliability of our 1018-nm FL as a practical 1-kW light source. Besides, an important investigation was made on the 1080-nm fiber laser tandem pumped by 1018-nm fiber lasers, the experimental result of which was reported to be 3712 W.

Magnitude and Spectrum of Electromagnetic Wave Scattered by Small Quadcopter in $X$ -Band

Estimation results of the magnitude and spectrum of electromagnetic wave scattered by small unmanned aerial vehicle with a radar cross section (RCS) of 0.01 m2 obtained by numerical simulation and direct measurements in an anechoic chamber at a frequency of 9 GHz and their comparison are discussed. Effectiveness of the parasitic leakage suppression technique at small RCS measurements has been shown.

Farmers’ knowledge, use and preferences of parasitic weed management strategies in rain-fed rice production systems

Rain-fed rice production in sub-Saharan Africa is often hampered by parasitic weeds. This study assessed farmers’ awareness, use, preference and adoption criteria of parasitic weed management practices in rain-fed rice production environments in Tanzania. Surveys and workshops were organized in three affected rice growing areas in Morogoro-rural, Songea and Kyela district, supplemented with on-farm experiments in Kyela. In all districts, farmers were aware of the locally occurring parasitic weed species, Rhamphicarpa fistulosa (lowland) and Striga asiatica (upland), and they considered these weeds more problematic than non-parasitic weeds. Though they mostly practise hand weeding, farmers were aware of a wide range of control options. Local access, affordability, ease of implementation and control efficacy were considered important criteria for adoption, whereas trade-offs, like lack of preferred grain quality traits in resistant varieties, were mentioned as an important break on adoption. Based on informal discussions with farmers, altered sowing times, resistant rice varieties and soil amendments were marked as feasible control options and tested in a farmer-participatory manner in four years of experimentation in upland and lowland fields. In both types of fields, the contribution of soil amendment to parasitic weed suppression was not evident, but rice husk was marked as a suitable and cheap alternative to inorganic fertilizers. Control of R. fistulosa in lowlands was perceived to be best realized by early crop establishment, escaping major parasite damage due to the relatively slow early development of this weed species. The local variety Supa India, appreciated for its grain qualities and marketability, remained the preferred variety. For the control of S. asiatica, late planting was preferred, requiring a short-duration variety to minimize risk of drought stress during grain filling. The short-duration NERICA-10 was most preferred, as it combined a favourable short cycle length with resistance to S. asiatica and good grain appearance. Farmer participation in technology testing showed to be crucial in defining locally adapted and acceptable parasitic weed control strategies. Yet, it is argued that without lifting important constraints related to credit and input supply, it will be impossible to sustainably solve the parasitic weed problem in rain-fed rice.

Free-space beam shaping for precise control and conversion of modes in optical fiber.

We consider the general problem of free-space beam shaping for coupling in and out of higher order modes (HOMs) in optical fibers with high purity and low loss. We compare the performance of two simple phase structures - binary phase plates (BPPs) and axicons - for converting Gaussian beams to HOMs and vice versa. Both axicons and BPPs allow for excitation of modes with high purity (>15 dB parasitic mode suppression), or conversion of HOMs to near-Gaussian beams (M2 < 1.25). Axicon coupling in single-clad fibers allows for lower loss (0.85 ± 0.1 dB) conversion than BPPs (1.7 ± 0.1 dB); but BPPs are compatible with any fiber design, and allow for rapid switching between modes. The experiments detailed here use all commercial components and fibers, allowing for a simple means to investigate the unique properties of multi-mode fibers.

Experimental study on parasitic mode suppression using FeSiAl in Relativistic Klystron Amplifier.

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE11 is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level, the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation.

The effects of hemiparasitic plant removal on community structure and seedling establishment in semi‐natural grasslands

AbstractQuestionHemiparasitic plants can profoundly affect the structure of the community in which they occur, mainly due to parasitic suppression of hosts. As a consequence, non‐host species have the opportunity to colonize resulting gaps. In contrast to most grassland species, hemiparasites are generally short‐lived and can reach high densities; as a consequence, vegetation gaps are left after their death. These gaps form microsites more suitable for seed germination and therefore might increase recruitment of other species. Which species suffer or profit from parasitism and is there a positive effect on seedling establishment?LocationSemi‐natural grasslands in northern Belgium.MethodsWe selected two hemiparasitic plant species from contrasting vegetation types: Rhinanthus angustifolius growing in mesotrophic grassland and Pedicularis sylvatica growing in oligotrophic heath‐grassland. A weeding experiment was set up at six sites in which the hemiparasite was repeatedly removed in half of the plots during three growing seasons. The abundance change of individual species was compared between weeded and control plots. After the second growing season, seeds of up to ten species were added. The number of seedlings in the third year was then compared between weeded and control plots.ResultsRhinanthus removal significantly affected the abundance of species relative to control plots, both positively and negatively, and decreased the species evenness. Pedicularis removal only increased the abundance of some species. Only Juncaceae (but no other graminoid families) increased after Rhinanthus and Pedicularis weeding, and there was considerable variation within functional groups. Moreover, based on our observations, we propose as a new hypothesis that species with persistent clonal spread are more vulnerable to parasitism. Once attached, resources are potentially drawn from a whole network of interconnected ramets. Finally, only half of the sown species successfully established seedlings; hemiparasite removal had a significantly negative effect on seedling number for two of these species.ConclusionsEffects of hemiparasites on species differ considerably, also within functional groups. Persistent clonal spread emerges as an important plant trait determining vulnerability to hemiparasites. Finally, our results suggest that hemiparasitic plants might have a limited positive effect on seedling establishment in these semi‐natural grasslands where chances for successful establishment were shown to be low.

Parasitic loss suppression in photonic and plasmonic photovoltaic light trapping structures.

In this paper, we examine the optical loss mechanisms and mitigation strategies in classical photovoltaic light trapping structures consisting of diffractive gratings integrated with a backside reflector, which couple normal incident solar radiation into guided modes in solar cells to enhance optical absorption. Parasitic absorption from metal or dielectric backside reflectors is identified to be a major loss contributor in such light trapping structures. We elucidate the optical loss mechanism based on the classical coupled mode theory. Further, a spacer design is proposed and validated through numerical simulations to significantly suppress the parasitic loss and improve solar cell performance.

Hemiparasitic litter additions alter gross nitrogen turnover in temperate semi-natural grassland soils

Hemiparasitic plants accumulate nutrients in their leaves and therefore produce high-quality litter with faster decomposition and nutrient release rates compared to non-parasitic litter. Higher levels of plant-available nitrogen (N) in the presence of hemiparasitic plants have been attributed to this ‘litter effect’, but effects on N dynamics in the soil remain unstudied. We tested the hypothesis that litter of Rhinanthus angustifolius and Pedicularis sylvatica increases N transformation rates in the soil more than non-parasitic litter of a species mix from the same communities. We expected the litter effect to be higher in the oligotrophic Pedicularis soil compared to the mesotrophic Rhinanthus soil. Gross N transformation rates were quantified using a 15N tracing modeling approach. Differentially 15N labeled NH4Cl + KNO3 was added to two soils with three treatments (control, soil amended with non-parasitic litter, soil amended with Rhinanthus or Pedicularis litter) in a laboratory incubation experiment. The concentration and 15N enrichment of NH4+ and NO3 in the soil were measured at six time points within one or two weeks (depending on the soil) after label addition. Hemiparasitic litter addition increased the overall cycling of N more compared to the addition of non-parasitic litter. Relative to the non-parasitic litter, addition of Rhinanthus litter increased the net flux from organic N to NH4+ by 61% and net (autotrophic) nitrification by 80%. Addition of Pedicularis litter increased the net flux from organic N to NH4+ by 28% relative to addition of non-parasitic litter, while there was no effect on nitrification. Surprisingly, gross mineralization of organic N to NH4+ decreased with litter addition for the Rhinanthus soil (control soil > non-parasitic litter > Rhinanthus litter), while it increased with litter addition in the Pedicularis soil (control soil < non-parasitic litter < Pedicularis litter). Our results support the hypothesis that litter from hemiparasitic plants increases soil N availability more than non-parasitic litter, but contradicts the expectation that the hemiparasitic litter effect would be more pronounced in an oligotrophic as compared to a mesotrophic system. This litter-induced augmentation in soil fertility provides – in addition to the parasitic suppression of hosts – a second potentially important pathway by which hemiparasitic plants impact on plant community composition. However, future research on P and K return via hemiparasitic litter should be considered.

Yb band parasitic lasing suppression in Er/Yb-co-doped pulsed fiber amplifier based on all-solid photonic bandgap fiber

A novel kind of all-solid photonic bandgap fiber (AS-PBGF) has been used in the master oscillator power amplifier structured Er/Yb-co-doped pulsed fiber amplifier to suppress the Yb band parasitic lasing for the power scaling and safety operation. To the best of our knowledge, this is the first time to report the use of AS-PBGF to suppress the Yb band parasitic lasing. The experimental results show that the Yb band parasitic lasing has been suppressed efficiently and the amplifier power has been raised dramatically with the utilization of AS-PBGF. An output power of 2.66 W was finally obtained without any unwanted parasitic lasing.

Parasitic lasing suppression in large-aperture Ti:sapphire amplifiers by optimizing the seed–pump time delay

Theoretical and experimental investigations are carried out to determine the influence of the time delay between the input seed pulse and pump pulses on transverse parasitic lasing in a Ti:sapphire amplifier with a diameter of 80 mm, which is clad by a refractive index-matched liquid doped with an absorber. When the time delay is optimized, a maximum output energy of 50.8 J is achieved at a pump energy of 105 J, which corresponds to a conversion efficiency of 47.5%. Based on the existing compressor, the laser system achieves a peak power of 1.26 PW with a 29.0 fs pulse duration.

Parasitic oscillation suppression in high-gain solid-state amplifiers

A method has been proposed for suppressing parasitic oscillation by processing the gain medium edges into arrises. The mode analysis indicates that the residual reflection at the gain medium edges decreases greatly and the required index matching level and the required cladding absorbency are reduced as well. With this method, a large choice of edge cladding material is allowed, which can help with avoiding distortion and other problems caused by thermal stress.

Integration of Complementary Metal–Oxide–Semiconductor 1-Bit Analog Selectors and Single-Electron Transistors Operating at Room Temperature

Silicon-based single-electron transistors (SETs) and complementary metal–oxide–semiconductor (CMOS) devices have been integrated onto a single chip, and the operation of SET/CMOS integrated circuits has been demonstrated at room temperature. The fabrication process of SETs has been improved in terms of parasitic resistance suppression, threshold voltage control, and reduction in required time for electron-beam lithography for integration with CMOS devices. There is no significant degradation in the characteristics of CMOS devices owing to the special fabrication process of SETs operating at room temperature. CMOS 1-bit analog selectors, which are building blocks of multibit address decoders, have been combined with SETs, and the circuit operation has been demonstrated at room temperature for the first time. These results show the feasibility of SET/CMOS integrated circuits composed of high-density arrays of SETs and high-performance CMOS peripheral circuits, which fully leverage the advantages of SETs and CMOS.

Nutrient input from hemiparasitic litter favors plant species with a fast-growth strategy

Hemiparasitic plants often produce nutrient-rich litter with high decomposition rates, and thus can enhance nutrient availability. When plant species have differential affinities for this nutrient source, hemiparasitic litter might influence species composition in addition to the parasitic suppression of host species. We expected that species adapted to fertile habitats derive a higher proportion of nutrients from the hemiparasitic litter compared to other species. 15N-labeled litter of Rhinanthus angustifolius and Pedicularis sylvatica was added to experimental field plots and adjacent litter bags. We examined N release from the litter, N uptake by the vegetation 2, 4 and 12 months after litter addition and differences in the proportion of N taken up from the litter (NL) between co-occurring species. The percentage of N in shoots of co-occurring plant species that is derived from the added hemiparasitic litter (NL) strongly differed between the species (0.1–6.2 %). After exclusion of species with an alternative N source (legumes as well as ectomycorrhizal and ericoid mycorrhizal species), NL was positively related (p < 0.001) with specific leaf area (SLA) and at Pedicularis sites with leaf N concentration (LNC) and leaf phosphorus concentration (LPC) (p < 0.05), i.e. leaf traits associated with a fast-growth strategy and adaptation to high-nutrient environments. Our results suggest that nutrient release from hemiparasitic litter favors plant species with a fast-growth strategy adapted to high-nutrient environments compared to species with a slow-growth strategy. Whether continued hemiparasitic litter inputs are able to change species composition in the long term requires further research.

New method of parasitic mode suppression in lateral-field-excited piezoelectric resonator

A new method of parasitic mode suppression in piezoelectric resonators with transverse (lateral) electric field is described, which employs the partial coverage of electrodes by a damping layer. The potential of the proposed method is demonstrated for a resonator based on an X-cut lithium niobate plate. It is experimentally confirmed that an acoustic wave with transverse electric polarization exhibits stiffening, the degree of which depends on both the electromechanical coupling coefficient and the wave aperture

Suppression criteria of parasitic mode oscillations in a gyrotron beam tunnel

This paper presents the design criteria of the parasitic mode oscillations suppression for a periodic, ceramic, and copper loaded gyrotron beam tunnel. In such a type of beam tunnel, the suppression of parasitic mode oscillations is an important design problem. A method of beam-wave coupling coefficient and its mathematical formulation are presented. The developed design criteria are used in the beam tunnel design of a 42 GHz gyrotron to be developed for the Indian TOKAMAK system. The role of the thickness and the radius of the beam tunnel copper rings to obtain the developed design criteria are also discussed. The commercially available electromagnetic code CST and the electron trajectory code EGUN are used for the simulations.

Design of a Femtosecond Ti:sapphire Laser for Generation and Temporal Optimization of 0.5-PW Laser Pulses at a 0.1-Hz Repetition Rate

A chirped-pulse amplification Ti:sapphire laser system has been designed using a 10-Hz 100-TW Ti:sapphire laser to generate 0.1-Hz 0.5-PW laser pulses and optimize their temporal qualities such as temporal contrast and pulse duration. A high-energy booster amplifier to be added is expected to produce an energy above 30 J through the parasitic lasing suppression and the efficient amplification. To improve the temporal contrast of the laser pulses, a high-contrast 1-kHz amplifier system is used as a front-end. A grating stretcher which makes the laser pulse have 1-ns duration is used to prevent optical damages due to high pulse energy during amplification. A grating compressor has been designed with group delay analysis to obtain the recompressed pulse duration close to the transform-limited pulse duration. The final laser pulses are expected to have energy above 20 J and duration below 40 fs.

High-Performance BOI FinFETs Based on Bulk-Silicon Substrate

A new body-on-insulator (BOI) FinFET device structure based on bulk-Si substrate has been proposed and experimentally demonstrated in this paper. In comparison with other bulk FinFETs, the BOI FinFET features the localized insulator below the Si-Fin body, which can achieve both low source/drain (S/D) parasitic resistance and effective suppression of the S/D leakage beneath the Si-Fin channel, as well as good heat dissipation capability. The device fabrication process is basically compatible with conventional CMOS technology. High drive current, low subthreshold swing, and excellent short-channel behavior are observed in the fabricated BOI FinFETs.

Evolution strategies optimization of the multiple Fabry-Perót imaging interferometer for the advanced technology solar telescope

We describe an evolutionary algorithm for the design of an imaging triple-étalon Fabry-Perót interferometer (MFPI), which gives a solution to the multidimensional minimization process through a stochastic search method. The interactions between design variables (the étalon reflectances, interétalon ghost attenuator transmittances, and spacing ratios) are complex, resulting in a fitness landscape that is pitted with local optima. Traditional least-squares and gradient descent algorithms are not useful in such a situation. Instead, we employ a method called evolution strategies in which several preliminary designs are randomly generated subject to constraints. These designs are combined in pairs to produce offspring designs. The offspring population is mutated randomly, and only the fittest designs of the combined population are passed to the next iteration of the evolutionary process. We discuss the evolution strategies method itself, as well as its application to the specific problem of the design of an incoherently coupled triple-étalon interferometer intended for use as a focal plane instrument in the planned National Solar Observatory's Advanced Technology Solar Telescope (NSO's ATST). The algorithm converges quickly to a reasonable design that is well within the constraints imposed on the design variables, and which fulfills all resolution, signal-to-noise, throughput, and parasitic band suppression requirements.

Parasitic Emission Suppression in Arrays of Individually Addressable Silicon Microcavity Plasma Devices

Full addressability of arrays of Si microcavity plasma devices has been demonstrated by adopting a split top electrode design. Arrays of pyramidal microcavities with emitting apertures of 100 times 100 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , a pixel pitch of 200 mum, and sizes as large as 512 times 512 pixels have been fabricated in 250-mum-thick Si(100) wafers. Parasitic capacitance is responsible for weak emission from adjacent microcavities when a single pixel is addressed but the suppression of nearest neighbor fluorescence with the current array design is ~6 dB. Any pixel in the array can be addressed with an rms voltage as low as 240 V when the array is operating in 500 torr of Ne.

Parasitic lasing suppression in high gain femtosecond petawatt Ti:sapphire amplifier

New parasitic lasing suppression techniques are developed and high gain amplification is demonstrated in a petawatt level Ti:sapphire amplifier based on the chirped pulse amplification (CPA) scheme. Cladding the large aperture Ti:sapphire with refractive-index matched liquid doped with absorber suppresses the transverse lasing. The acousto-optic programmable dispersive filter (AOPDF) is used to realize side-lobe suppression in the temporal profile of the compressed pulse. The 800 nm laser output with peak power of 0.89 PW and pulse width of 29.0 fs is demonstrated.