Adjacent Emitters Research Articles

Effect of emitter tip spacing on Si vacuum field emitter arrays

This paper presents a qualitative and quantitative analysis of close-packed vacuum field emitter arrays. Through a combination of computational simulations and experimental verifications, the relationship between emitter spacing and electric field screening is studied. In order to obtain a uniform electron emission and large current densities from a field emitter array, it is essential to minimize the screening effect between the adjacent field emitters. As previously demonstrated, sharpening the emitter tips, reducing the background doping concentration of the emitters, and reducing the anode–cathode distance can suppress the screening effect. Field emitter arrays with different sizes and emitter spacings are fabricated and characterized. Decreasing the array size and increasing emitter spacing lead to a larger average current per emitter (19 nA/tip at an anode voltage of 250 V). However, larger current densities (up to 3.3 A/cm2) are observed in close-packed arrays. In very large arrays with a small emitter spacing, the current is scaled with the emitter area (∼4.2 nA/emitter at an anode voltage of 250 V), indicating a small current contribution from the sides of the array.

Spectral-combined beam characteristics based on external cavity feedback diode laser array

In spectral beam combining systems, the locked spectra of the diode laser array are determined by the interaction between the internal cavity and the external cavity. Using the multibeam interference theory, spectral modes locked by the coupled cavity are numerically calculated and analyzed. A spectral mode of a diode emitter is divided into a main lobe, a left sidelobe, and a right sidelobe, which is mainly affected by the position of the diode emitter. Based on the locked spectral modes, a beam propagation model in the grating-external cavity is established by the diffraction integral method and the incoherent superposition principle. The effects of the interval between two adjacent emitters, the reflectivity of the front surface, and the distance between the grating and the coupler on the characteristics of the combined beam have been discussed in detail. The results show that the beam quality and the spot size of the combined beam gradually degrade with the increasing interval. By reducing the reflectivity of the front surface of the diode emitter and decreasing the distance between the grating and the coupler, the beam quality can be improved. Among the three factors, such as the interval between two adjacent emitters, the reflectivity of the front surface of an emitter, and the diffraction distance, the interval has the most sensitive impact on the combined beam characteristics. Thus a beam shrinker to convert big beams into small beams in diameter can be adopted to optimize the combined beam.

Beam parameter product optimization of densely arranged multi‐emitter tunnel junction cascaded laser

AbstractA tunnel junction cascaded semiconductor laser with thin waveguide and narrowed spacing between adjacent emitters is designed in this work. It can be concluded theoretically that the spatial size of the spots arrangement in fast axis has a greater impact on the vertical beam parameter product (BPP) of the multi‐emitter cascaded laser than the divergence angle. The measured vertical BPP of the designed narrow emitter spacing (NES) laser has been reduced 42.5%, which implies that the beam quality performance of the laser has been improved and proves the feasibility of this method. Meanwhile, the slope efficiency of the thin waveguide NES laser can reach up to 3.55 W/A under 10 ns duration pulse current.

Low Divergence Angle Output in Tunnel Junction Cascade Laser With in-Phase Mode Operation

In this study, we report a novel laser with in-phase super-mode coupled double emitter cascaded by tunnel junction. By incorporating a mode expansion layer on the P-type side of the upper emitter to suppress other high-order modes, pure in-phase fundamental mode operation demonstrated via far-field measurements and simulations is realized in the fast-axis direction with a slope efficiency of 2.08 W/A driven by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100~\mu \text{s}$ </tex-math></inline-formula> , 100Hz quasi-continuous wave (QCW) bias current. More importantly, the only central peak of emitted in-phase mode has a low vertical far-field divergence angle of 12.69° due to the coupled design of the two adjacent emitters. The novel mode coupling structure has obvious benefits for the practical application of tunnel junction lasers in LIDAR detection areas.

Non-uniform optical phased array with a large steering angle and high side mode suppression ratio.

An optical phased array (OPA) is one of the most promising methods of light detection and ranging. A non-uniform array with different emitter distances is a method to realize OPA steering without grating lobes or a distance between two adjacent emitters larger than λ/2. However, the side mode suppression ratio (SMSR) will decrease as OPA turns into a large angle. In this paper, 64-, 128-, and 256-channel non-uniform OPAs are optimized by non-dominated sorting genetic algorithm-II (NSGA-II), which is a multi-objective optimization algorithm. Compared with arrays optimized by a genetic algorithm, the SMSR at 80° improves by 2.18, 2.61, and 2.56dB, respectively.

Nanoscale Focus Pinspot for High-Purity Quantum Emitters via Focused-Ion-Beam-Induced Luminescence Quenching.

Epitaxially grown quantum dots (QDs), especially embedded in photonic structures, play an essential role in various quantum photonic systems as on-demand single-photon sources. However, these QDs often suffer from adjacent unwanted emitters, which contribute to the background noise of the QD emission and fundamentally limit the single-photon purity. In this paper, a nanoscale focus pinspot (NFP) technique using focused-ion-beam-induced luminescence quenching enables us to improve single-photon purity from site-controlled QD as a proof-of-concept experiment. The optical quality of the QD emission is not degraded while the signal-to-noise ratio of the QD is improved. Moreover, the QD after the NFP technique reveals the single-photon nature at further elevated temperatures owing to the reduced background noise. As the NFP technique is nondestructive, it retains the apparent physical structures and photonic functions, thereby indicating its promising potential for applying diverse high-purity quantum emitters, particularly integrated in photonic devices and circuits.

DeepSTORM3D: dense 3D localization microscopy and PSF design by deep learning.

Localization microscopy is an imaging technique in which the positions of individual point emitters (e.g. fluorescent molecules) are precisely determined from their images. This is a key ingredient in single/multiple-particle-tracking and super-resolution microscopy. Localization in three-dimensions (3D) can be performed by modifying the image that a point-source creates on the camera, namely, the point-spread function (PSF). The PSF is engineered to vary distinctively with emitter depth, using additional optical elements. However, localizing multiple adjacent emitters in 3D poses a significant algorithmic challenge, due to the lateral overlap of their PSFs. Here, we train a neural network to localize multiple emitters with densely overlapping PSFs over a large axial range. Furthermore, we then use the network to design the optimal PSF for the multi-emitter case. We demonstrate our approach experimentally with super-resolution reconstructions of mitochondria and volumetric imaging of fluorescently labeled telomeres in cells.

Scale Law of Far-Field Thermal Radiation from Plasmonic Metasurfaces.

Although metamaterials or metasurfaces consisting of patterned subwavelength structures have been widely employed for thermal emission control, the collective behavior of the emitter array in a metasurface still remains unclear. Here, based on the quasinormal mode theory, we derive a new scale law to elucidate the far-field thermal emission from a metasurface composed of densely packed plasmonic nanoemitters. The tight binding method is used to approximate the collective resonant mode of the emitter array. Because of in-phase near-field interaction, the thermal radiation from a single emitter in a metasurface is suppressed by its adjacent emitters. We find that the overall far-field thermal radiation from a metasurface can be either positively or negatively correlated with the packing density of the emitters, depending on the mode properties of the single emitter. This new scale law thus serves as a general guideline for designing metasurfaces with desired thermal emission properties.

Generalized characteristics of expanded sector beams formed by phased antenna arrays obtained by scaling phase distributions

This paper considers specific features of the phase synthesis of expanded sector beams formed by phased antenna arrays by the method of fan partial diagrams. Partial radiation patterns are formed by pairs of adjacent emitters. The synthesis results have the property of scaling, which allows many expansion options to be obtained on the basis of one expansion option. This is achieved by multiplying the phase shift values of the signals from all emitters by the same value. It is shown that, when the beam expands along the sum channel, a radiation pattern with an extended angular distance between the maxima is formed in the difference channel. An analysis of the initial sections of the difference radiation patterns in the formation of expanded beams of the sum radiation pattern was conducted. The behaviour of the generalized characteristics of expanded beams across the range of expansion coefficients was analysed. The conclusion was made about the possibility of timely and predictable control of the width of the difference radiation pattern of a phased antenna array

Ultrastrong coupling in single plexcitonic nanocubes

Abstract Light-matter strong coupling is defined when the coupling strength exceeds the losses in the system, whereas ultrastrong coupling is not simply strong coupling with even larger coupling strength. Instead, ultrastrong coupling regime arises when the coupling strength is comparable to the transition frequency in the system. At present, ultrastrong light-matter interactions have been achieved in superconducting circuits, semiconductor polaritons, and organic molecules, where these systems are typically at the micrometer scale. In this work, we investigated ultrastrong coupling in a nanoparticle plexcitonic system, i.e. a single gold nanocube coated with quantum emitters and positioned on a gold film. We observed a normalized coupling rate η ~ 0.12 to the antenna mode in such coated nanocube-on-mirror (c-NCoM) configuration at the multilayer emitter level. In contrast to the gap mode that squeezes all the optical fields into the gap region, the antenna mode in c-NCoM provides multiple exterior hot spots at the upper corners of the nanocube, which can be exploited for qubit entanglement within a single nanocube. The concurrence between adjacent emitters is estimated up to 0.6. This theoretical study establishes a promising route toward building a scalable quantum network using single plexcitonic nanocubes as quantum nodes.

Theoretical Investigations of the Ultrasonic Wave Generation by an Electromagnetic Acoustic Transducer

Background. The article considers the analysis of the electromagnetic acoustic (EMA) converter with controlled angular input of acoustic waves, using parameters influencing the formation of an acoustic wave.Objective. The aim of the paper is to analyze the formation of an acoustic wave with angular input in the EMA converters of non-destructive testing systems.Methods. Mathematical modelling was used to investigate the influence of the distance from the yarn-emitters to the control object surface. The influence of various factors (current magnitudes, external magnetic field values, distance from the yarn-emitter and the grating to the control object surface) is investigated with the help of mathematical modeling.Results. The optimal value of the magnetic induction of an external magnetic field is shown. The calculation of the pressure created by the yarn-emitters and the grating on the controlled object surface was carried out. A formula for the ultrasonic wave input angle was obtained. The formula depends on the parameters of the control environment, the distance between the emitters, the phase shift between the harmonic current signals applied to the adjacent emitters and the harmonic signal frequency. It was found that a change in the angle between the EMA transducer and the surface of the control object leads to a significant deterioration in the acoustic wave generation on the surface of the controlled object.Conclusions. We investigated the possibility of the angular input of an ultrasonic wave using system of parallel-arranged yarn-emitters. A decrease in the acoustic pressure, with increasing distance from the yarn-emitters to the controlled object surface was observed.

Effect of crosstalk on combined beam characteristics in spectral beam combining systems

In a spectral beam combining (SBC) system, crosstalk always happens because stray lights are inevitable due to fabrication errors of optical components and ‘smile’ effect of laser arrays. Two kinds of crosstalk, including the crosstalk generated between two adjacent emitters of the laser array (ad-crosstalk) and that generated between two non-adjacent emitters (non-ad-crosstalk), have been analyzed. The equivalent light of the crosstalk model has been proposed, and the propagation model of the SBC system with the crosstalk has been built up. On this basis, influences of above two kinds of the crosstalk on the combined beam have been numerically simulated and discussed in detail. The results show that the wavelength composition of the combined beam varies evidently owing to the existence of the crosstalk. With the increasing of the crosstalk intensity, the beam quality of the combined beam degrades, and the side lobes of intensity distribution of the combined beam become more and more obvious. Furthermore, the influence of the non-ad-crosstalk on the beam quality is more serious than that of the ad-crosstalk.

Dependence of optimal spacing on applied field in ungated field emitter arrays

In ungated field emitter arrays, the field enhancement factor β of each emitter tip is reduced below the value it would have in isolation due to the presence of adjacent emitters, an effect known as shielding or screening. Reducing the distance b between emitters increases the density of emission sites, but also reduces the emission per site, leading to the existence of an optimal spacing that maximizes the array current. Most researchers have identified that this optimal spacing is comparable to the emitter height h, although there is disagreement about the exact optimization. Here, we develop a procedure to determine the dependence of this optimal spacing on the applied electric field. It is shown that the nature of this dependence is governed by the shape of the β(b) curve, and that for typical curves, the optimal value of the emitter spacing b decreases as the applied field increases.

EFFECT OF IRRIGATION INTERVALS AND DIFFERENT PLANT DENSITIES ON FABA BEAN YIELD, SOME WATER RELATIONS AND SOME SOIL PROPERTIES UNDER DRIP IRRIGATION SYSTEM IN NORTH MIDDLE NILE DELTA REGION.

EFFECT OF IRRIGATION INTERVALS AND DIFFERENT PLANT DENSITIES ON FABA BEAN YIELD, SOME WATER RELATIONS AND SOME SOIL PROPERTIES UNDER DRIP IRRIGATION SYSTEM IN NORTH MIDDLE NILE DELTA REGION.

Improved field emission properties from carbon nanotubes grown onto micron-sized arrayed silicon pillars with pyramidal bases

Carbon nanotubes (CNTs) were synthesized onto micron-sized arrayed silicon (Si) pillars with pyramidal bases in order to mitigate the electric-field-screening due to densely grown CNTs. Compared with the CNT emitters grown on a flat Si substrate, CNT emitters grown on arrayed Si pillars showed improved field emission properties with a low turn-on field of 2.16V/μm at 10μA/cm2 and current density of 550μA/cm2 at 3.46V/μm. Field enhancement factor was calculated according to the Fowler–Nordheim theory. The resultant field enhancement factor of CNT emitters on arrayed Si pillars was higher than that of CNT emitters on a flat substrate, which revealed that the formation of arrayed Si pillars could be an effective method to suppress electric-field-screening among adjacent CNT emitters.

Estimation of water consumption as affected by measurement locations of soil water content in drip irrigated tomato in solar greenhouses

土壤水分传感器埋设位置的选择是局部灌溉条件下获得作物根区代表性土壤含水率数据, 从而制定滴灌灌溉制度的关键。本文以日光温室滴灌番茄为对象, 研究滴灌线源土壤湿润体内含水率分布状况, 通过对比距滴灌带不同位置处土壤含水率监测结果估算番茄耗水量的差异, 探讨土壤含水率监测的合理位置。结果表明, 番茄生育期内14~25 mm的灌水定额主要用于增加0~40 cm土层的土壤含水率, 湿润体内日平均土壤含水率分布在75%~100%田间持水率。作物生育期内连续多次滴灌条件下, 沿滴灌带单个灌水器形成的湿润土体会充分叠加, 形成近似均匀的土壤含水率带状分布, 且作物生育期内沿深度方向0~40 cm土层土壤含水率均值无显著性差异, 距滴灌带不同水平距离的土壤含水率随时间的变化趋势具有同步特点, 无明显的滞后性。以集中80%总根量的土壤深度作为滴灌番茄水分渗漏下界面时, 14~25 mm的灌水定额会导致深层渗漏, 且深层渗漏量表现出一定的空间变异性。番茄生育期内深层渗漏量约占灌水量的13%。距滴灌带不同位置处的番茄耗水量除在番茄苗期和开花座果期有较大差异外, 其余生育阶段的差异均在10%以内。对温室滴灌番茄来说, 滴灌高频少量的灌溉特征有利于维持作物根系层适宜的土壤水分状态, 监测1个含水率剖面即可满足估算作物耗水量的要求。

In-Phase Coherently-Coupled Optically-Pumped VECSEL Array

We report on an optically pumped vertical-external-cavity surface-emitting laser array exhibiting coherent coupling. Imaging of the far field shows interference consistent with in-phase coherent coupling, and a majority of total power is present in the central on-axis lobe. The physical mechanism of operation is attributed to diffractive coupling, wherein a small portion of the light emitting from each emitter is shared with adjacent emitters of the array.

Localization precision of stochastic optical localization nanoscopy using single frames

The Cramer-Rao lower bound (CRLB) on localization precision of unbiased estimators is analyzed for stochastic optical localization nanoscopy that localizes emitters frame by frame independently. It is found that the CRLB is a function of the mean number of detected photons per emitter, signal to Poisson noise ratio, signal to Gaussian noise ratio, point spread function (PSF), pixel size, and relationship of emitter locations. With a slight and practical approximation, effect of Gaussian noise is equivalent to increasing the mean photon count of Poisson noise by a number equal to the variance of Gaussian noise. Numerical examples demonstrate that the CRLB of emitters located on a curve increase fast as the distance of adjacent emitters increases. The mean CRLB of randomly uniformly distributed emitters in both two-dimensional and three-dimensional imaging increases exponentially fast as the emitter density increases. The effects of PSF, standard deviation of PSF, mean number of detected photons per emitter, signal to noise ratio, axial thickness, and pixel size on the CRLB are also numerically investigated. The analytical and numerical results provide a guideline for the design of location estimators and a benchmark for the achievable localization precision of stochastic optical localization nanoscopy.

High-multiple spontaneous otoacoustic emissions confirm theory of local tuned oscillators

Understanding the origin of spontaneous otoacoustic emissions (SOAEs) in mammals has been a challenge for more than three decades. Right from the beginning two mutually exclusive concepts were explored. After 30 years this has now resulted in two well established but incompatible theories, the global standing-wave theory and the local oscillator theory. The outcome of this controversy will be important for our understanding of inner ear functions, because local tuned oscillators in the cochlea would indicate the possibility of frequency analysis via local resonance also in mammals. A previously unexploited opportunity to gain further information on this matter lies in the occasional cases of high-multiple SOAEs in human ears, which present a large number of adjacent small frequency intervals. Here, eight healthy ears of four subjects (12 to 32 SOAEs per ear) are compared with individually simulated ears where frequency spacing was random-generated by two different techniques. Further, a group of 1000 ears was simulated presenting a mean of 21.3 SOAEs per ear. The simulations indicate that the typical frequency spacing of human SOAEs may be due to random distribution of emitters along the cochlea plus a graded probability of mutual close-range suppression between adjacent emitters. It was found that the distribution of frequency intervals of SOAEs shows no above-chance probability of multiples of the preferred minimum distance (PMD) between SOAEs and that the size of PMD is related to SOAE density. The variation in size between adjacent small intervals is not significantly different in random-generated than in measured data. These three results are not in agreement with the global standing-wave theory but are in line with the local oscillator theory. In conclusion, the results are consistent with intrinsic tuning of cochlear outer hair cells.

A high-density 3D localization algorithm for stochastic optical reconstruction microscopy.

Stochastic optical reconstruction microscopy (STORM) and related methods achieves sub-diffraction-limit image resolution through sequential activation and localization of individual fluorophores. The analysis of image data from these methods has typically been confined to the sparse activation regime where the density of activated fluorophores is sufficiently low such that there is minimal overlap between the images of adjacent emitters. Recently several methods have been reported for analyzing higher density data, allowing partial overlap between adjacent emitters. However, these methods have so far been limited to two-dimensional imaging, in which the point spread function (PSF) of each emitter is assumed to be identical. In this work, we present a method to analyze high-density super-resolution data in three dimensions, where the images of individual fluorophores not only overlap, but also have varying PSFs that depend on the z positions of the fluorophores. This approach can accurately analyze data sets with an emitter density five times higher than previously possible with sparse emitter analysis algorithms. We applied this algorithm to the analysis of data sets taken from membrane-labeled retina and brain tissues which contain a high-density of labels, and obtained substantially improved super-resolution image quality.