Emission Intensity Profiles Research Articles

Ion temperature and rotation velocity measurements of carbon and boron ions using VUV spectroscopy on EAST.

A space-resolved vacuum ultraviolet spectroscopy is employed to measure impurity emission profiles (500-3200Å) on EAST. This study successfully captures C IV (1548.20 and 1550.77Å) lines emitted from carbon ions and derives ion temperatures using Doppler broadening and a collision model based on their intensity ratios. Both the emission intensity and ion temperature profiles are determined. However, the calculated results reveal a lower temperature of around 10-20eV with the collision model, suggesting a potential need for further correction in subsequent calculations. Furthermore, this study explores relative rotation velocities from the Doppler shift, indicating an increase in toroidal rotation velocity with applied neutral beam injection. The measured results exhibit concordance with the charge exchange recombination spectrometer data. Furthermore, during boron powder dropping discharges on EAST, B II (1623.60, 1623.79, 1623.95, 1624.02, 1624.17, and 1624.38Å) emission lines exhibiting a similar time behavior trend with boron powder injection are identified. Ion temperatures are measured using B II (1362.46Å) through the Doppler broadening method. These techniques hold significant promise for future impurity analysis at the edge of EAST, providing valuable insights into the behavior of carbon and boron ions.

Simple Characterization of Cylindrical Diffuser Fibers With a Fluorescent Layer.

A fast, simple, versatile, and reliable method to record light emission intensity profiles of cylindrical light diffusers (CDFs) in air and transparent liquids has been developed. A fluorescent color glass filter (RG695) converts red light emitted by a cylindrical diffuser fiber into near-infrared light in an emission angle-independent manner. The red light was provided from a diode laser system at 635 nm. Near-infrared fluorescence from the RG695 was imaged with a camera. Images from this camera were processed to obtain emission intensity profiles. Cylindrical diffuser fiber profiles of four different manufacturers were compared. The proposed method provides angle-independent intensity profiles of cylindrical diffuser fibers with a single camera shot. It could be demonstrated that dependent on the underlying principle of how the diffuser fiber tips emit light, the emission profile can change significantly in media with different refractive indices. By converting the light emitted by a diffuser fiber tip into fluorescence light one can eliminate the dependence of the recorded profile on the emission angle from the diffusor. This approach allows for easily taking into account refraction-index (mis)matching by placing the equipment into a suitable liquid. The proposed measurement principle bears potential for quality assurance measurements of CDFs used for interstitial laser thermotherapy or photodynamic therapy.

Spatio-temporal analysis of power deposition and vibrational excitation in pulsed N2 microwave discharges from 1D fluid modelling and experiments

Vibrational excitation of N2 beyond thermodynamic equilibrium enhances the reactivity of this molecule and the production of radicals. Experimentally measured temporal and spatial profiles of gas and vibrational temperature show that strong vibrational non-equilibrium is found in a pulsed microwave discharges at moderate pressure (25 mbar) in pure N2 outside the plasma core and as an effect of power pulsing. A one dimensional radial time-resolved self-consistent fluid model has been developed to study the mechanism of formation of vibrationally excited N2. In addition to the temperature maps, time-resolved measurements of spontaneous optical emission, electron density and electron temperature are used to validate the model and the choice of input power density. The model reveals two regions in the plasma: a core where chemistry is dominated by power deposition and where vibrational excitation starts within the first ∼10 µs and an outer region reliant on radial transport, where vibrational excitation is activated slowly during the whole length of the pulse (200 µs). The two regions are separated by a sharp gradient in the estimated deposited power density, which is revealed to be wider than the emission intensity profile used to estimate the plasma size. The low concentration of excited species outside the core prevents the gas from heating and the reduced quenching rates prevent the destruction of vibrationally excited N2, thereby maintaining the observed high non-equilibrium.

Highly polarized light emission from hybrid of quantum dots and plasmons in the intermediate coupling regime.

Colloidal semiconductor quantum dots (QDs), with a size tunable bandgap and remarkably high quantum efficiency, have been recognized as ideal light sources in quantum information and light emitting devices. For light sources, besides the emission intensity and spectral profile, the degree of polarization (DoP) is an essential parameter. Here, by embedding a monolayer of QDs inside the nanogap between a bottom Au mirror and a top Ag nanowire, we have demonstrated highly polarized light emission from the QDs with an average DoP of 0.89. In addition to the anisotropic photoluminescence (PL) intensity, the PL spectra are distinct at different polarizations, with an asymmetric spectral shape or even two-peak features. Such an anisotropic emission behavior arises from the coupling between the QDs and the largely confined and polarization-dependent gap-plasmons in the Au/QD/Ag nanocavities in the intermediate coupling regime. Our results demonstrate the possibility of achieving highly polarized light sources by coupling spherical QDs to single anisotropic plasmonic nanocavities, to provide new opportunities in the future design of polarized QD-based display devices.

Quantification of plasma produced OH and electron fluxes at the liquid anode and their role in plasma driven solution electrochemistry

Plasma–liquid interactions enable various applications through the generation of a large range of reactive species in solution. In this work, we report on the interaction of a pulsed atmospheric pressure glow-like discharge with a liquid anode. Particularly, the flux of hydroxyl (OH) radicals and electrons in the plasma at the liquid anode are measured by laser induced fluorescence (LIF) spectroscopy and current measurements to investigate the role of OH and electrons in plasma-enabled redox chemistry in solution. The impact of the voltage pulse width, voltage amplitude, liquid temperature and conductivity on the OH density distribution was also investigated. We observed a significant OH density near the liquid surface, which showed a transition from a ring-shaped structure to a more uniform structure with increasing plasma power. This transition coincided with a similar transition in the plasma emission intensity and electron density profile. A Raman laser scattering study indicated that this transition can be attributed to an enhanced N2 mixing at larger plasma-dissipated powers. Besides, a time resolved measurement showed that the OH density segregates radially in the afterglow at velocities exceeding the gas velocity at room temperature due to enhanced gas convection resulting from the plasma-induced gas heating. While the OH flux was of the order of ∼1021 m−2 s−1, approximately two orders of magnitude lower than the electron flux, significant reduction in the solution occurs during the voltage pulse. Nonetheless, a slow oxidation was observed in the afterglow due to the much longer lifetime of OH radicals compared to electrons. The Faradaic efficiency of the liquid redox chemistry was evaluated with H cell measurements and showed a good agreement with a 1D liquid phase model with the measured electron and OH fluxes as the input. This result shows the capability to quantitatively describe the plasma-driven solution electrochemistry for a model redox couple based on OH and electron driven reactions.

Two-dimensional electron temperature and density profiles of Hall thruster plume plasmas using tomographically reconstructed optical emission spectroscopy

Two-dimensional electron temperature and density profiles in the plume region of 300 W-class Hall thruster Ar plasmas were obtained using tomographically reconstructed optical emission intensity profiles combined with a collisional-radiative (CR) model. A total of 1242 lines of sight were used by rotating the thruster to apply inverse Radon transform-based tomographic reconstructions and Abel inversion. The reconstruction accuracy of the developed diagnostic system was evaluated using a priori images derived from plasma pictures, and the reconstruction error was less than 1% in the region of interest, exhibiting higher accuracy than the Abel inversion. From the Ar Hall thruster plasma, more than 12 different two-dimensional profiles of Ar I emission intensity within a spectral range of 600–1000 nm were obtained 6 mm from the exit plane of the thruster. A CR model using 31 allowed transitions at 15 different states from the ground state to the 2p i states was incorporated with the tomographically reconstructed emission intensity sets. Consequently, two-dimensional electron temperature and density profiles in the range of 5–18 eV and 2.0 × 1016–4.7 × 1017 m−3 were obtained, respectively, exhibiting reasonable agreement with the double Langmuir probe measurements.

Controlling Single‐Photon Emission with Ultrathin Transdimensional Plasmonic Films

AbstractThe properties of a two‐level quantum dipole emitter near an ultrathin transdimensional plasmonic film are studied theoretically. The model system studied mimics a solid‐state single‐photon source device. Using realistic experimental parameters, the spontaneous and stimulated emission intensity profiles are computed as functions of the excitation frequency and film thickness, followed by the analysis of the second‐order photon correlations to explore the photon antibunching effect. It is shown that ultrathin transdimensional plasmonic films can greatly improve photon antibunching with thickness reduction, which allows one to control the quantum properties of light and make them more pronounced. Knowledge of these features is advantageous for solid‐state single‐photon source device engineering and overall for the development of the new integrated quantum photonics material platform based on the transdimensional plasmonic films.

Probing the Density Fine Structuring of the Solar Corona with Comet Lovejoy

The passage of sungrazing comets in the solar corona can be a powerful tool to probe the local plasma properties. Here, we carry out a study of the striae pattern appearing in the tail of sungrazing Comet Lovejoy, as observed by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO) during the inbound and outbound phases of the comet’s orbit. We consider the images in EUV in the 171 Å bandpass, where emission from oxygen ions O4+ and O5+ is found. The striae are described as due to a beam of ions injected along the local magnetic field, with the initial beam velocity decaying because of collisions. Also, ion collisional diffusion contributes to ion propagation. Both the collision time for velocity decay and the diffusion coefficient for spatial spreading depend on the ambient plasma density. A probabilistic description of the ion beam density along the magnetic field is developed, where the beam position is given by the velocity decay and the spreading of diffusing ions is described by a Gaussian probability distribution. Profiles of emission intensity along the magnetic field are computed and compared with the profiles along the striae observed by AIA, showing a good agreement for most considered striae. The inferred coronal densities are then compared with a hydrostatic model of the solar corona. The results confirm that the coronal density is strongly spatially structured.

Effects of Nd3+ doping content on microstructure and spectral properties of Nd:SrF2 transparent ceramic

0.5–5 % (atom percent) Nd3+-doped SrF2 transparent ceramics were fabricated by hot-pressed sintering and the effects of Nd3+ doping content on microstructure and spectral properties were studied. With Nd3+ content increased from 0.5 % to 5 %, in-line transmittance of Nd:SrF2 ceramic at 1060 nm increased from 15.8 % to 85.3 %. FE-SEM micrographs showed the grain growth was inhibited and the microstructure became more compact and homogenous. Emission spectra revealed that concentration quenching was occurred at Nd3+ content of 1–2 %. Emission lifetime of 4F3/2 energy level monotonously decreased from 1805.4 μs to 19.6 μs. Evolution profiles of emission intensity and lifetime of Nd:SrF2 transparent ceramic with Nd3+ doping content were proposed. The appropriate Nd3+ content for spectral properties of Nd:SrF2 transparent ceramic was found around 1 %. The results demonstrated Nd:SrF2 transparent ceramic has large emission lifetime and mild concentration quenching effect, indicating that Nd3+-doped SrF2 transparent ceramics could be more promising gain media for all-solid-state lasers than other Nd3+-doped alkaline-earth fluorides.

Model for Nitric oxide and its dayglow emission in the martian upper atmosphere using NGIMS/MAVEN measured neutral and ion densities

A comprehensive study of Nitric oxide (NO) chemistry in the Martian upper atmosphere is restricted due to the lack of requisite measurements. NO is an abundant form of odd nitrogen species in the Martian lower atmosphere and its density depends on several photochemical processes. We have developed a photochemical model to study the NO density in the dayside of Martian upper atmosphere by accounting for various production and loss mechanisms. By utilizing the Neutral Gas and Ion Mass Spectrometer (NGIMS) on-board Mars Atmosphere and Volatile Evolution (MAVEN) mission measured neutral and ion densities during deep dip 8 and 9 campaigns, we modelled NO number density in the Martian sunlit upper atmosphere for the altitudes between 120 and 200 km. The modelled NO densities are employed to calculate NO (1,0) γ band emission intensity profiles in the dayside upper atmosphere of Mars. The calculated NO density and its γ band intensity profiles are found to be consistent with Imaging Ultraviolet Spectrograph (IUVS) onboard MAVEN observations and also with other modelling studies. We found that the local CO2 and N2 density variations can lead to a change in NO density and consequently its dayglow intensity by a factor of 2 to 5. Since NO is a trace constituent and also its dayglow emissions are strongly obscured by CO Cameron band emissions, we suggest that the derivation of NO number density based on our approach can constrain its abundance in the dayside upper atmosphere of Mars. More observations of (1-0) γ band emission along with modelling will help to study the global distribution of NO in the Martian atmosphere.

Resolving discharge parameters from atomic oxygen emission

A method is proposed to spatially resolve discharge parameters from experimental measurements of emission intensity and 1D numerical simulations including an O atom collisional-radiative model. The method can be used for different plasmas and conditions. Here, contracted microwave discharges for CO2 conversion are studied at intermediate to high pressures (100–300 mbar). Radial profiles of electron density (n e) are used as input in the model and corrected to successfully simulate the measured Gaussian profiles of emission intensity of the 777 nm transition (I 777). As a result, radially-resolved parameters inaccessible in experiments, such as n e, power density (P abs), electron temperature (T e), electric field and reaction rates, are numerically-obtained for several conditions. n e and P abs approximately follow Gaussian profiles that are broader than that of I 777. For pressures below 150 mbar, the difference in full width at half maximum is typically a factor 1.6. This consists in a phenomenon of optical contraction, which is due to concave profiles of O molar fraction and T e. The implications of the simulated profiles on the study of plasmas for CO2 conversion are discussed and it is shown that these profiles allow to explain high reactor performances at low pressures.

Mexican Small‐Scale Fisheries Reveal New Insights into Low‐Carbon Seafood and “Climate‐Friendly” Fisheries Management

As a society, we are confronted with the question of how best to feed an expanding human population, and some have pointed to seafood as a “climate‐friendly” option. To date, the contributions of small‐scale fisheries (SSFs) have been largely excluded from studies on food footprint. Here, we calculated the Emission Intensity profiles for seven seafood types generated by Mexican SSFs. Based on these results—which indicate that there exist several low‐carbon SSFs in Northwestern Mexico—we provide a coarse approximation for the total carbon footprint of Mexico’s motorized small‐scale fleet. Finally, we scrutinize the utility of non‐fuel data (such as GPS data) in predicting fuel consumption/carbon emissions across SSFs. To our knowledge, this is the first life‐cycle assessment to compare multiple seafood products generated by Mexican SSFs, and the first published link between tracking data and carbon accounting for SSFs specifically. We discuss how these results, in combination with insights gained from monitoring efforts in Northwestern Mexico, might be used to inform and incentivize “climate‐friendly” fisheries management. While carbon footprint represents just one component of sustainability, this article serves as a helpful case study for those preoccupied with carbon accounting and fishers sustainability in traditionally data‐limited scenarios.

High-spatial-resolution image reconstruction-based method for measuring electron temperature and density of the very near field of an applied-field magnetoplasmadynamic thruster

A method based on image reconstruction is proposed for measuring the electron temperature () and density () distribution of the axisymmetric low-temperature argon plasma plume of applied-field magnetoplasmadynamic thrusters (AF-MPDTs). The method uses a complementary metal–oxide–semiconductor camera with narrowband filters of 460 and 500 nm to obtain the raw projection images in specific wavelength ranges. An image reconstruction method is developed to construct relative emission intensity profiles. The electron temperature distribution can be obtained by combining the relative emission intensity ratio of two profiles with a simple argon kinetic model. The electron density distribution can be calculated by constructing a function of relative emission intensity containing and . To verify the feasibility of this method, we diagnosed a very near field plume of a 15 kW AF-MPDT and obtained the distribution of parameters with a spatial resolution of 0.23 mm. The results show that the maximum and are located on the centerline near the exit plane of the thruster and decrease with both radial and axial distances. The second peak appears in the radial direction of both the and distributions, while their zones do not overlap. A comparative analysis of measurement results obtained by this method and the Langmuir probe method is performed to prove its accuracy. Moreover, this measurement method has the advantages of high spatial resolution and the ability to diagnose high-density and magnetized plasma. This method can be also applied to other optically thin axisymmetric low-temperature argon plasmas.

Numerical simulation of an atmospheric pressure plasma jet with coaxial shielding gas

A two-dimensional (r, z) numerical simulation of the discharge characteristics of an atmospheric pressure plasma jet (APPJ), with coaxial shielding gas, was performed. The helium working gas flowed in a central capillary tube, engulfing a needle electrode powered by 13.7 MHz radio frequency sinusoidal voltage. The N2 shielding gas flowed in the annular space of a coaxial tube. These gases emerged, in laminar flow, in a 78%N2-21%O2-1%Ar dry air ambient. The characteristics of the APPJ with shielding gas were compared to those of the APPJ without shielding gas. The nitrogen shielding gas hindered the diffusion of oxygen and argon from the ambient air into the helium jet. With the shielding gas present, more nitrogen penetrated into the helium core, causing a shorter plasma ‘plume’. The flow rates of the working and shielding gas, critically affected the gas temperature, and in turn the discharge characteristics. For a He flow of 2 standard liters per minute (slm), switching on the nitrogen shielding gas flow (at 4.5 slm) reduced the on-axis O2 and Ar mole fractions from to and from to , respectively, at an axial distance of 3 mm downstream of the nozzle. The radial profiles of the mole fractions of the ambient gases were monotonically and strongly decreasing towards the system axis, for short axial distances from the nozzle (∼1 mm), but became progressively flatter at longer distances from the nozzle (3 mm and 5 mm). Simulation predictions captured the salient features of experimental data of ambient species mole fractions in the plasma jet, and the 706 nm optical emission intensity profiles of the He 33S excited state.

High-speed multi-spectral imaging of the hypergolic ignition of ammonia borane

Recently, ammonia borane (a hydrogen-dense solid fuel) has received increased attention as a potential fuel for use in hybrid rocket systems due to its potential for higher performance. Ammonia borane (AB) is also highly hypergolic with white fuming nitric acid (WFNA) while lacking the health hazards associated with more conventional hypergolic fuels (e.g. hydrazine and its derivatives). To date, there remains a lack of information regarding the combustion behavior of ammonia borane. This work makes use of simultaneous visible and infrared multi-spectral imaging to study the combustion behavior of AB during a hypergolic ignition event (with reagent grade nitric acid droplets applied to the AB as the oxidizer). Using optical filters corresponding to previously reported spectral bands, emission from BO, BO2, HBO2, and the B-H stretch mode of AB were selectively imaged. A two-step ignition process consisting of an initial gas evolution step followed by a separate, seemingly premixed flame propagation step was observed. Observation of HBO2 emission during the pre-ignition/gas evolution phase suggests that rapid formation of HBO2 occurs even at the lower temperatures present prior to ignition. This initial formation of HBO2 (and the subsequent heat release associated with it) may be a major driver of AB/nitric acid decomposition. Emission intensity profiles obtained after the AB samples began burning with the ambient air suggests some degree of HBO2 consumption within the flame front, seemingly counter to the current understanding that HBO2 is a stable product species. This may indicate that boron combustion via boranes may proceed to more complete combustion than is typical for more conventional boron fuels. The ignition dynamics and sequence of boron product formation was well-captured by the multi-spectral imaging technique applied to this reaction system for the first time. This technique could be applied for further study of other boron systems.

Tunable white light emission in zinc phosphate glasses activated with [formula omitted] clusters and Sm3+

Zinc phosphate glasses, activated with Agmn+ clusters and Sm3+, were prepared by the conventional melt-quenching method. The X-ray diffraction patterns revealed that the samples remain amorphous for Ag and Sm3+ contents up to 3.0 and 1.0 mol%, respectively. The Raman and FTIR spectra showed that the main vibrational modes are associated with P–O bonds. The absorption coefficient spectrum of the Ag singly doped glass sample displayed a broad band centered at 318 nm, related to Agmn+ clusters, whereas those co-doped with Sm3+ showed, in addition to the Agmn+ cluster absorption, the well-known Sm3+ absorptions at 343, 360, 374, 401, 415, 438, 465 and 477 nm. The photoluminescence excitation spectrum of the Ag singly doped glass sample exhibited a broadband from 3 to 6 eV (207–413 nm), assigned to superposition of the Ag+: 4 d10 → 4d95s and Agmn+ cluster: S0 → S1 transitions, being the excitation into the Agmn+ clusters attractive for W-LEDs applications. The photoluminescence emission spectra of the Ag singly doped glass sample, upon Agmn+ cluster excitations at 340, 350 and 360 nm, displayed cold white light tonality, with (0.279, 0.300) CIE1931 chromaticity coordinates of 9453 K and bluish-white light tonality with (0.264, 0.276) and (0.259, 0.270) CIE1931 chromaticity coordinates and correlated color temperature values of 12901 and 14201 K, respectively. The global emission of the Ag and Sm3+ co-doped glass samples was, upon 340, 350 and 360 nm excitations, gradually tuned from the bluish and cold white region to the warm white one, as the Sm3+ content was increased, with correlated color temperatures in the 14201-2691 K range. The Sm.3+ emission bands, under excitations at 340 and 350 nm, were attained at expense of radiative and non-radiative energy transfer from the Agmn+ clusters, as revealed respectively by the sinks mounted on the Agmn+ cluster emission bands and the emission decay profile shortening in presence of Sm3+. Analysis of the Agmn+ cluster emission intensity and decay profiles, with the Dexter and Burstein models, showed that Agmn+ cluster cross-relaxation and/or non-radiative energy transfer to Sm3+ might be dominated by an electric quadrupole-quadrupole interaction.

Directional light emission enhancement from LED-phosphor converters using dielectric Vogel spiral arrays

Increasing light extraction efficiency and narrowing the angular spread of light emitted from optically thick light emitting diodes (LEDs) are desirable but difficult goals to achieve. In this paper, we design, optimize, and fabricate Vogel spiral arrays of dielectric nanostructures for optical directional extraction enhancement of incoherent emission from optically thick phosphor-converted LEDs. In order to design and optimize large-scale structures, we perform a systematic numerical investigation based on full-vector three-dimensional finite difference time domain simulations using a cloud of randomly positioned and randomly phased dipoles that approximate an incoherent Lambertian source. An analytical model based on kinematic scattering is also developed and used to parametrically study changes in the emission profile as the spiral geometry is tuned. The optimal Vogel spiral arrays are fabricated as TiO2 nanodisks atop YAG:Ce3+ blue-to-white converter layers using electron-beam lithography and reactive ion etching. Photoluminescence spectroscopy is used to experimentally measure extraction enhancement up to 2× compared to a flat reference. Finally, accurate Fourier-space (k-space) fluorescence spectroscopy is used to measure the emission intensity profile up to 54° in a single snapshot image, and we find up to a 35% enhancement in power-normalized forward emission compared to a flat reference, under remote laser excitation. The integration of optimized Vogel spiral arrays of dielectric nanoparticles with phosphor-converted LEDs will increase efficiency and narrow the directional spread of light. These effects are beneficial to a variety of active device applications, including imaging, lighting, and projecting devices that require enhanced extraction efficiency combined with directional emission.

Recombination activity of threading dislocations in GaInP influenced by growth temperature

Room-temperature non-radiative recombination is studied at single dislocations in Ga0.5In0.5P quantum wells grown on metamorphic templates using cathodoluminescence and electron channeling contrast imaging. An analysis of the light emission intensity profiles around single dislocations reveals that the average recombination strength of a dislocation decreases by a factor of four and seven as a result of decreasing growth temperature of the GaInP quantum well from 725 to 675 and 625 °C, respectively. This reduction occurs despite little change in the diffusion length, precluding the prospect of inducing carrier localization by ordering and phase separation in GaInP at lower growth temperatures. These observations are rationalized by the premise that point defects or impurities are largely responsible for the recombination activity of dislocations, and the extent of decoration of the dislocation core decreases with temperature. Preliminary evidence for the impact of the Burgers vector is also presented. The lowest growth temperature, however, negatively impacts light emission away from dislocations. Carrier recombination in the bulk and at dislocations needs to be considered together for metamorphic devices, and this work can lead to new techniques to limit non-radiative recombination.

Room-temperature two-color lasing by current injection into a GaAs/AlGaAs coupled multilayer cavity fabricated by wafer bonding

Room-temperature two-color lasing was demonstrated by current injection into a GaAs/AlGaAs coupled multilayer cavity for terahertz emitting devices utilizing its difference-frequency generation (DFG) inside the structure. We prepared two epitaxial wafers with (001) and (113)B orientations and they were directly bonded to form the coupled multilayer cavity. The (001) side cavity contains two types of InGaAs multiple quantum wells to realize optical gain for two-color lasing while a single GaAs layer of the (113)B side cavity is a nonlinear medium for efficient DFG. Lasing behavior was clearly observed for two modes under pulsed current conditions at room temperature. We found that the intensity relation between two-color lasings was dependent on the pulse duration because of the different temporal profiles of emission intensity. Simultaneous two-color lasing in the device was also confirmed by measuring the sum-frequency generation signal using a beta barium borate crystal.

Uniform emission, constant wavevector silicon grating surface emitter for beam steering with ultra-sharp instantaneous field-of-view.

We report on uniform emission intensity profile, uniform propagation constant silicon gratings for beam steering application with ultra-sharp instantaneous field-of-view (IFOV). To achieve uniform emission intensity across relatively long emission length, we designed a custom grating with varying Si3N4 width and duty cycle while maintaining a uniform propagation constant for relatively narrow divergence emission pattern. We designed and fabricated the custom Si3N4/Si grating with the varying Si3N4 width/duty cycle together with the reference Si3N4/Si grating with a constant 50:50 duty cycle. The custom grating demonstrated the beam steering angle value of 6.6° by sweeping wavelength between 1530 nm and 1575 nm with the emission length over 1 mm. The measured IFOV based on the 3-dB beamwidth values of the far field patterns for the TE polarization are 0.10° and 0.75° for the custom grating and for the reference grating, respectively. The custom grating also indicates mode-selective behavior due to the perturbation of propagation constant for input modes other than TE polarization. The measured TE-mode to TM-mode suppression ratio for the custom grating is approximately 8.2 dB peak-to-peak measured at far field.