Large Angular Aperture Research Articles

Analysis of Phase Mismatch for Mercurous Bromide-Based Non-Collinear AOTF Design in Spectral Imaging Applications.

The spectral and spatial characteristics of Acousto-Optic Tunable Filters (AOTFs), such as a tuning curve, spectral resolution, angular aperture, and diffraction efficiency, are determined by the device's acousto-optic crystal configuration and piezoelectric transducer. For high-throughput spectral imaging applications, it is essential to enlarge the spectral bandwidth and angular aperture during the design phase of AOTFs. Thus, phase mismatch due to incident angle or wavelength was studied analytically using phase diagrams in this paper. Additionally, a performance parameter analysis model was established based on the use of mercurous bromide crystals for large angular aperture AOTF device design, and the impact of crystal and transducer design parameters on the spectral bandwidth and angular aperture was evaluated. This also experimentally validates the diffraction capability of AOTFs made from mercurous bromide crystal, which possess a broad spectral transmission ability ranging from visible to long-wave infrared.

Pitch Angle Distribution of MeV Electrons in the Magnetosphere of Jupiter

AbstractThe magnetosphere of Jupiter harbors the most extreme fluxes of MeV electrons in the solar system and therefore provides a testbed of choice to understand the origin, transport, acceleration, and loss of energetic electrons in planetary magnetospheres. Along this objective, the Pitch Angle Distribution (PAD) of energetic electrons may reveal signatures of the dominant physical processes. Here, we analyze for the first time the PAD of MeV electrons observed by the Galileo‐Energetic Particle Detector (EPD) experiment in orbit around Jupiter from 1995 to 2003. We find that the MeV electron PADs observed by the integral channels of EPD appear relatively isotropic with a flux anisotropy lower than a factor of 3. Due to the relatively large angular apertures of the EPD telescopes, the actual anisotropy may be larger than the observed one. The fine anisotropy observed by Galileo‐EPD reveals persistent pancake distributions at the M‐shell of M = 9. Outward of this distance, at M = 15 and M = 20–60, MeV electron distributions have pancake, isotropic, and scattered beam field‐aligned distributions. The scattered beam distributions can either be evidence of outward adiabatic transport or may suggest that high‐latitude auroral acceleration can transiently supply as much trapped MeV electrons to the middle magnetosphere as the inward adiabatic transport of electrons from an outer equatorial reservoir.

Spatiospectral transformation of noncollimated light beams diffracted by ultrasound in birefringent crystals

Spatiospectral structure of wave phase matching in birefringent crystals has a strong dependence on the geometry of the acousto-optic interaction and incident light spectrum. This dependence defines details of light beam profile transformation. It is especially important for imaging applications related to a large angular aperture and a wide spectral bandwidth of the incident light. In this paper, we demonstrate accurate three-dimensional plotting of a light transmission pattern without small birefringence approximation. The rather complicated shape of the phase-matching locus in the spatiospectral domain inevitably leads to residual spatially nonuniform chromatic aberrations in the spectral image. Theoretical consideration and computational modeling are confirmed by the experiments on Bragg diffraction in paratellurite crystal. The results are especially important for the development of acousto-optical imaging devices and laser beam shaping technologies.

Optoelectronic Device for Molecular Orientation of Functional Materials

A new approach to the development of an optoelectronic device for molecular orientation of functional materials is proposed. Results of the development of its main components are presented: a collimator for the light from an LED and a broad band polarizer with a large angular aperture. The problem of the collimation of a strongly diverging beam from an LED is examined. It is shown that the use of a modified conical lens offers promise for solving this problem. A broad-band polarizer with a large angular aperture, which is an important component of the optoelectronic device, is developed and fabricated on the basis of a multilayered structure.

Solar Concentrator Modules for Residential Power Supply

Currently, in many areas with a centralized energy supply, there is much concern about energy performance of buildings, and therefore, there is a growing interest in the use of integrated solar concentrator modules (SCMs), which reduce the need for centralized electricity and heat supply. Of greater interest are nontracking SCMs, since their relatively large angular aperture allows operation without solar tracking. The objective of this study is to improve SCM efficiency and reduce the cost of electricity and heat generation. The SCM mathematical model is implemented in the OptiCad software. SCMs have been developed with low cosine losses, long service life, and low cost. The developed SCM design makes it possible to reduce cosine losses in comparison with a solar module without a concentrator by 3–15 times and increase the duration of SCM operation in a stationary mode by 6–9 months per year. The cost of the concentrator and the receiver developed using SCMs is 50% of the module cost, respectively. The cost of the developed SCMs in comparison with flat ones from China will be decreased by 1.64 times. The developed SCMs can be used for residential power supply in a stationary design for roofs and facades and with tracking systems for ground installation.

Limits on field of view for Risley prisms.

The constraints on directions of incoming and outgoing rays of Risley prisms, caused by total internal reflection and surface tilt, are investigated for the four typical configurations. After applying a nonparaxial ray-tracing method based on the vector form Snell's law, the incident angles at prisms' surfaces are calculated and compared with the critical angle. On this basis, the direction limitations of incoming and outgoing rays are investigated. The permissible incoming directions as well as the achievable outgoing directions depend on prisms' orientation. Their ranges over which the rays can pass through the system at any prism orientation are defined as the angular aperture and angular field of view (FOV). The effects of the prisms' refractive index, opening angle, and arrangement on angular aperture/FOV are discussed. It is shown that there exists a direct trade-off between the deviation power and the angular aperture/FOV for Risley prisms, that is, high refractive index and large opening angle yield a smaller angle aperture/FOV. Large angular aperture can be achieved by employing the 2121 configuration, while it is desirable to adopt a 1212 configuration to obtain large angular FOV. The research can afford guidance for prism material, geometry choices, and configuration setting in the design of a Risley prism system for wide-angle beam steering or imaging adjustment.

Spatiotemporal analysis of high-performance military aircraft noise during ground run-up

Recent measurements of high-performance military aircraft noise have revealed that full-scale jet noise has features and structures that are still only partly understood, such as the presence of multiple acoustic radiation lobes in the aft direction at certain frequencies. Spatiotemporal analyses of a ground-based microphone array measurement of the noise from a tethered F-35 at various engine conditions are used to investigate these features of the sound field. The ground array covered an angular aperture of 35–152 degrees relative to the front of the aircraft. The large angular aperture allows for a detailed investigation of the correlation and coherence at frequencies exhibiting multi-lobe behavior. This spatiotemporal analysis yields further evidence of the characteristics of multi-lobe behavior in high-performance, full-scale jet noise. [Work supported by an Office of Naval Research grant, a USAFRL SBIR, and the F-35 JPO. Distribution A: Approved for public release; distribution unlimited. Cleared 07/10/2017; JSF17-714.]

Characterization of broadband shock-associated noise from high-performance military aircraft

For nonideally expanded jets, broadband shock-associated noise (BBSAN) is a feature in the sideline and forward directions. While BBSAN has been studied fairly extensively for laboratory-scale jets, its presence and characteristics in full-scale, tactical aircraft noise need to be evaluated. Noise measurements on a tied-down F-35 provide the opportunity to characterize full-scale BBSAN using a linear ground array that spanned a large angular aperture: 35–152 degrees relative to the front of the aircraft. The main questions are whether the full-scale BBSAN shares the same characteristics as those observed in laboratory-scale BBSAN and if current models capture the features of full-scale BBSAN. The variation in the spectral shape, peak frequency, and peak level of full-scale BBSAN across angle for different engine powers is explored and compared to prior laboratory studies. Comparisons are also made with models for BBSAN based on stochastic theory ([Tam et al., J. Sound Vib. 140, 55–71 (1990)]) and the simplified model used in Kuo et al. [AIAA Paper 2011–1032 (2011)] for lab-scale BBSAN. Frequency-dependent convective speed estimates obtained from the current BBSAN models are compared to estimates based on directivity. [Work supported by the Office of Naval Research and the F-35 JPO.]

Evolution of the ultrasonic resonance modes in a three-layer structure with change of material and interface adhesion properties

The quantitative non-destructive evaluation (NDE) of interface adhesion has long been a challenge for the safe use of bonding structures. It is difficult to predict the adhesion resistance force between adhesive and adhered material without performing destructive testing. Ultrasonic approach seems to be the only potential way for its NDE based on the reason of mechanical nature of the problem. Different ultrasonic techniques, such as bulk wave echography, reflection resonance, and Lamb guided waves, have been used to evaluate the interface adhesion strength. But no direct relation between the interfacial bonding strength and the ultrasonic measurement has been established. The most used compression wave echography and resonance at normal incidence are less sensitive to the interface condition, except for a disbond. It is essential that the interface should be excited with a shear stress component to increase the measurement sensibility. But it is not easy to excite the interface by using shear waves in experiment, while the use of guided waves will encounter the problems of high attenuation and mode selection as all modes are not sensitive to a certain interface in a bonded structure. A previous study has shown that the V (z) inversion technique can be used to perform a multimode measurement on a layered structure, where both compression and shear stress resonance occur. This method has the advantage in using a simple experimental setup working at the normal incidence with a focus transducer of large angular aperture. The inversed angular-frequency reflectance function R(; f) gives the resonance modes which are equivalent to the Lamb type guided modes, while it is a local determination of the wave mode, thus the difficulty in guided wave measurement above mentioned can be avoided. The first part of the paper contains the development of the theoretical model for wave propagation in a multilayered structure where three-layer sandwich bonded structures can be considered as a particular case. A weak interfacial adhesion is described by two interface compression and shear stiffness parameters, namely km and kt. By integrating the transfer matrix formalism under the non-ideal boundary conditions, the plane wave angular (incident angle) and frequency reflection coefficient function R(; f) for a liquid immersed asymmetric metal-adhesive-metal three-layer and its dispersion curves of guided mode waves with or without charge are calculated. It is confirmed that the evolutions of the reflection zeros (mode resonances) correspond to the dispersion curves of the guided waves of the same structure without charge. Furthermore, the resonance modes observed in R(; f) can be considered as a combination of the respective Lamb modes of the top and bottom single metal layers coupled through the modes conditioned by the middle adhesive layer and the its interface conditions. The second part of the paper shows the behaviors of the resonance modes by changing the parameters related to the bonding strength. The acoustical impedance, the mass density and the thickness of the adhesive layer, which are related to the cohesive property, and the shear interfacial stiffness coefficient kt which conditions the adhesive property, are changed respectively to observe the resonance mode evolutions. The mode evolutions due to each parameter are analyzed and differentiated. It can be concluded that the change in the adhesion strength of the bonding structure does not affect significantly the modes belonging to those inherent to the two adhered aluminum layers, while the coupling modes will be shifted in frequency and exchange with or replace the said inherent modes. It is expected that the obtained results in this study will be of significance for quantitatively characterizing the interfacial properties of an adhesively bonded layered structure by using the V (z) inversion technique.

The V(z) Inversion Technique for Evaluation of an Adhesively Bonded Structure**Supported by the Key Program of the National Natural Science Foundation of China under Grant Nos 10834009 and 11374230

Based on the fact that the evolution trace in incident angle and frequency of the resonance zeros of the reflection coefficient function for a water charged layered medium is equivalent to its guided wave mode dispersion, the interfacial adhesion of a three-layer aluminum–adhesive–aluminum bonding structure is characterized nondestructively by determining the interface shear stiffness kt associated with the interfacial strength. The resonance reflection function is obtained experimentally by the V(z) inversion technique using an ultrasonic focused transducer of wide-band and large angular aperture (up to ±45°). The dispersion curves are numerically calculated, adjusting the parameter kt so that the difference between the dispersion curves and the angular-frequency tracing of the reflection zeros is minimum. The parameter kt at an interface of weakly adhered aluminum epoxy-resin is estimated to be 1014 N/m3.

Stitching interferometry for cylindrical optics with large angular aperture

Stitching interferometry is an attractive method for measuring optics with large apertures. However, existing stitching algorithms are not suitable for measuring cylindrical optics, because the misalignment aberrations in cylindrical interferometry are more complicated than those in plane, spherical and aspherical measurements. This paper presents a stitching algorithm for measuring cylindrical optics with large angular apertures. With it, we use five aberrations (i.e. piston, tilt, tip, defocus and twist) to describe the possible misalignments of the tested cylindrical surface and to build the cylindrical stitching model. Using this model allows us to calculate the relative misalignment aberrations of subapertures from their overlapped areas, so that the full aperture map of a cylindrical surface is obtained by compensating for these misalignment aberrations. In experiment, a cylindrical lens with an angular aperture over 150° is measured, thus demonstrating the feasibility and validity of the proposed method.

Dynamic scattering of electron vortex beams--a Bloch wave analysis.

Two important applications of electron vortex beams are in electron magnetic chiral dichroism (EMCD) measurements and nanoparticle manipulation. In both cases orbital angular momentum (〈Lz〉) transfer between the vortex beam and the specimen due to dynamic scattering is critical. In general the 〈Lz〉 pendellösung consists of short and long wavelength oscillations. The former is due to interference between the tightly bound 1s and more dispersive non-1s Bloch states, while the latter is due to interference between the non-1s states. For EMCD experiments with ±ħ angular momentum beams, momentum transfer can be minimised by selecting the appropriate aperture size, so that the probe wavefunction approximately matches that of the 2p-type Bloch states. For manipulating nanoparticles with large angular momentum beams small apertures are required to excite the 1s state and thereby enhance the short wavelength oscillations in 〈Lz〉. This enables efficient momentum transfer to the specimen, provided the nanoparticle dimension corresponds to a minimum in the 〈Lz〉 pendellösung.

X-ray microlaminography with polycapillary optics

We demonstrate layer-by-layer x-ray microimaging using polycapillary optics. The depth resolution is achieved without sample or source rotation and in a way similar to classical tomography or laminography. The method takes advantage from large angular apertures of polycapillary optics and from their specific microstructure, which is treated as a coded aperture. The imaging geometry is compatible with polychromatic x-ray sources and with scanning and confocal x-ray fluorescence setups.

Similarity spectra analysis of high-performance jet aircraft noise

Noise measured in the vicinity of an F-22A Raptor has been compared to similarity spectra found previously to represent mixing noise from large-scale and fine-scale turbulent structures in laboratory-scale jet plumes. Comparisons have been made for three engine conditions using ground-based sideline microphones, which covered a large angular aperture. Even though the nozzle geometry is complex and the jet is nonideally expanded, the similarity spectra do agree with large portions of the measured spectra. Toward the sideline, the fine-scale similarity spectrum is used, while the large-scale similarity spectrum provides a good fit to the area of maximum radiation. Combinations of the two similarity spectra are shown to match the data in between those regions. Surprisingly, a combination of the two is also shown to match the data at the farthest aft angle. However, at high frequencies the degree of congruity between the similarity and the measured spectra changes with engine condition and angle. At the higher engine conditions, there is a systematically shallower measured high-frequency slope, with the largest discrepancy occurring in the regions of maximum radiation.

Three‐dimensional optoacoustic tomography using a conventional ultrasound linear detector array: Whole‐body tomographic system for small animals

Optoacoustic imaging relies on the detection of ultrasonic waves induced by laser pulse excitations to map optical absorption in biological tissue. A tomographic geometry employing a conventional ultrasound linear detector array for volumetric optoacoustic imaging is reported. The geometry is based on a translate-rotate scanning motion of the detector array, and capitalizes on the geometrical characteristics of the transducer assembly to provide a large solid angular detection aperture. A system for three-dimensional whole-body optoacoustic tomography of small animals is implemented. The detection geometry was tested using a 128-element linear array (5.0∕7.0 MHz, Acuson L7, Siemens), moved by steps with a rotation∕translation stage assembly. Translation and rotation range of 13.5 mm and 180°, respectively, were implemented. Optoacoustic emissions were induced in tissue-mimicking phantoms and ex vivo mice using a pulsed laser operating in the near-IR spectral range at 760 nm. Volumetric images were formed using a filtered backprojection algorithm. The resolution of the optoacoustic tomography system was measured to be better than 130 μm in-plane and 330 μm in elevation (full width half maximum), and to be homogenous along a 15 mm diameter cross section due to the translate-rotate scanning geometry. Whole-body volumetric optoacoustic images of mice were performed ex vivo, and imaged organs and blood vessels through the intact abdominal and head regions were correlated to the mouse anatomy. Overall, the feasibility of three-dimensional and high-resolution whole-body optoacoustic imaging of small animal using a conventional linear array was demonstrated. Furthermore, the scanning geometry may be used for other linear arrays and is therefore expected to be of great interest for optoacoustic tomography at macroscopic and mesoscopic scale. Specifically, conventional detector arrays with higher central frequencies may be investigated.

A hemispherical retarding field energy analyzer to characterize spatially and angularly extended electron beams

We have designed and built a hemispherical retarding field energy analyzer in order to facilitate characterization of large area electron emitters (typically field emitter arrays with active areas up to 1 cm2) with large angular aperture. A complete numerical model of the analyzer has been built, including perturbations due to secondary particles, in order to determine the analyzer performances. The analyzer energy resolution is better than 100 meV for an energy range up to 120 eV. The analyzer has a global field of view of 112° and allows measurements of the energy distribution of the beam as a function of the emission angle, as well as measurements of the beam intensity profile along any section of the beam. We have successfully used the analyzer to characterize the electron beam emitted by 1 cm2 Mo microtips-based field emitter arrays.

Enhancement of Laser Interaction with Vacuum for a Large Angular Aperture

We study the nonlinear interaction of laser light with vacuum for a large angular aperture at electromagnetic field strengths far below the Schwinger limit. The polarization and magnetization in vacuum irradiated by a focused laser beam clearly differ from those in matter. This is due to the dependence on the Lorentz invariant, which results in a ring-shaped radiation distribution in vacuum. The number of the radiated photons increases nonlinearly with increasing angular aperture.

Spectral resolution enhancement of acousto-optic tunable filter by double-filtering

The development of the large angular aperture noncollinear acousto-optic tunable filter (AOTF) is based on the parallel tangents momentum-matching condition. In this letter, we have introduced a special double-filtering method that leads to an enhancement of the spectral resolution. And the birefringence together with the rotatory property of the interaction material has been considered to ensure the accuracy of designing an AOTF. The principle and availability of double-filtering are discussed in detail. It is confirmed that double-filtering method is effective to enhance the spectral resolution on the condition of keeping the quality of imaging, which is significant in practical applications of imaging AOTF.

P-74: Calibration of a Fourier-Optics based Measurement System

We present new calibration tools dedicated to the last generation of Fourier optics viewing angle instruments developed at ELDIM. These instruments are capable to measure luminance and color at any azimuth and quasi all the incidence angles up to ±88°. Accurate measurements at grazing angles are extremely difficult to realize by any technique just because of geometrical questions. The paper presents the procedure developed to calibrate the angles and the optical axis of the instrument, and its capacity to measure accurately the luminance and color in such a large angular aperture.

Framing shadowgraphy of 266nm laser probing for the diagnosis of Z-pinch plasmas

Framing shadowgraphy of UV laser probing with the 4th harmonic Nd-YAG Laser was developed for the diagnosis of Z-pinch plasmas. This system can effectively shield visible light and has advantages of high temporal resolution, large optical angular aperture and wide measuring range. The designed parameters and experimental results in implosions of tungsten wire array are presented in this paper.