scholarly journals Polarization Independent Achromatic Meta-Lens Designed for the Terahertz Domain

2020 ◽  
Vol 8 ◽  
Author(s):  
Yufei Gao ◽  
Jianqiang Gu ◽  
Ridong Jia ◽  
Zhen Tian ◽  
Chunmei Ouyang ◽  
...  
Keyword(s):  
Focal Length ◽  
Chromatic Aberration ◽  
Amplitude Distribution ◽  
Full Width ◽  
Half Maximum ◽  
Transmission Amplitude ◽  
Planar Lens ◽  
Polarization Insensitive ◽  
Silicon Based ◽  
Polarization Independent

In recent years, metasurface-based focusing elements have gradually become an indispensable type of terahertz lenses. However, the meta-lens often suffers from chromatic aberration due to the intrinsic dispersion of each element, especially in the broadband application scenarios. In this paper, we design and demonstrate a silicon-based achromatic meta-lens working from 0.6 to 1.0 THz, which is polarization insensitive because of the adopted symmetrical structures. The simulated focal length and the full width at half maximum (FWHM) of the foci at different frequencies prove the achromatic behavior of our meta-lens compared with the chromatic counterpart. We also show that the focus shift incongruence of our design originates from the transmission amplitude distribution of the meta-lens. This article not only provides an achromatic planar lens working at terahertz domain but also reveals the importance of the amplitude distribution in the achromatic metasurface design.

scholarly journals Large-aperture refractive lenses for momentum-resolved spectroscopy with hard X-rays

2013 ◽  
Vol 20 (4) ◽  
pp. 591-595 ◽  
Author(s):  
Hiroshi Fukui ◽  
Markus Simon ◽  
Vladimir Nazmov ◽  
Jürgen Mohr ◽  
Kenneth Evans-Lutterodt ◽  
...  
Keyword(s):  
Focal Length ◽  
X Rays ◽  
Full Width ◽  
Half Maximum ◽  
One Dimensional ◽  
Large Aperture ◽  
Effective Aperture

One-dimensional kinoform and prism refractive lenses with large aperture and high transmittance at 22 keV have been investigated. A 12.0 µm focus size (full width at half-maximum) and an effective aperture of 0.85 mm, at a focal length of 705 mm and 21.747 keV, were achieved.

scholarly journals Diffraction-limited axial double foci and optical traps generated by optimization-free planar lens

Nanophotonics ◽  
2020 ◽  
Vol 9 (4) ◽  
pp. 841-853 ◽  
Author(s):  
Long Ma ◽  
Jian Guan ◽  
Yiqun Wang ◽  
Chen Chen ◽  
Jianlong Zhang ◽  
...  
Keyword(s):  
Focal Length ◽  
Numerical Aperture ◽  
Nano Particles ◽  
Optical Traps ◽  
Optical Forces ◽  
Half Maximum ◽  
Particle Trapping ◽  
Planar Lens ◽  
Dielectric Particles ◽  
Good Uniformity

AbstractAxial diffraction-limited multiple foci are a kind of investigated focal field for trapping multiple nano-particles. We first experimentally generated diffraction-limited axial double foci by optimization-free binary planar lens and theoretically demonstrated it, which can be applied in multi-particle trapping. The proposed binary planar lens was analytically designed. The BPL has a numerical aperture of 0.9 and a focal length of 150 μm. The focal field of the binary planar lens, which is composed of diffraction-limited axial double foci, was first experimentally validated. The measured maximum lateral full widths at half maximum of the two generated focal spots were diffraction-limited and consistent with the theoretical. The axial double foci formed two stable optical traps that can trap two Rayleigh dielectric particles simultaneously. The radial, azimuthal and axial optical forces of the double optical traps are in good uniformity, which are 0.98, 0.99 and 0.96, respectively.

The Reduction of Chromatic Aberrations Due to Instrumental Instabilities

1971 ◽  
Vol 29 ◽  
pp. 14-15
Author(s):  
J. S. Lally ◽  
R. Evans
Keyword(s):  
Electron Microscope ◽  
High Voltage ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Usual Practice ◽  
Voltage Electron ◽  
Short Focal Length ◽  
Chromatic Aberrations ◽  
Electron Microscopes

One of the instrumental factors often limiting the resolution of the electron microscope is image defocussing due to changes in accelerating voltage or objective lens current. This factor is particularly important in high voltage electron microscopes both because of the higher voltages and lens currents required but also because of the inherently longer focal lengths, i.e. 6 mm in contrast to 1.5-2.2 mm for modern short focal length objectives.The usual practice in commercial electron microscopes is to design separately stabilized accelerating voltage and lens supplies. In this case chromatic aberration in the image is caused by the random and independent fluctuations of both the high voltage and objective lens current.

Comparison of Deterministic and Linear Cosine Spatial Filtering of Transmission Electron Micrographs

1972 ◽  
Vol 30 ◽  
pp. 596-597
Author(s):  
David A. Ansley
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Spatial Filter ◽  
Operating Conditions ◽  
Objective Lens ◽  
List Type ◽  
Spatial Filters ◽  
Transmission Electron ◽  
Wide Range

The coherence of the electron flux of a transmission electron microscope (TEM) limits the direct application of deconvolution techniques which have been used successfully on unmanned spacecraft programs. The theory assumes noncoherent illumination. Deconvolution of a TEM micrograph will, therefore, in general produce spurious detail rather than improved resolution.A primary goal of our research is to study the performance of several types of linear spatial filters as a function of specimen contrast, phase, and coherence. We have, therefore, developed a one-dimensional analysis and plotting program to simulate a wide 'range of operating conditions of the TEM, including adjustment of the:(1) Specimen amplitude, phase, and separation(2) Illumination wavelength, half-angle, and tilt(3) Objective lens focal length and aperture width(4) Spherical aberration, defocus, and chromatic aberration focus shift(5) Detector gamma, additive, and multiplicative noise constants(6) Type of spatial filter: linear cosine, linear sine, or deterministic

scholarly journals Recording site placement on planar silicon-based probes affects signal quality in acute neuronal recordings

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Richárd Fiáth ◽  
Domokos Meszéna ◽  
Zoltán Somogyvári ◽  
Mihály Boda ◽  
Péter Barthó ◽  
...  
Keyword(s):  
Single Unit ◽  
Brain Activity ◽  
Amplitude Distribution ◽  
High Amplitude ◽  
Neural Implants ◽  
Recording Site ◽  
Significant Difference ◽  
Planar Silicon ◽  
Silicon Based ◽  
Unit Yield

AbstractMultisite, silicon-based probes are widely used tools to record the electrical activity of neuronal populations. Several physical features of these devices are designed to improve their recording performance. Here, our goal was to investigate whether the position of recording sites on the silicon shank might affect the quality of the recorded neural signal in acute experiments. Neural recordings obtained with five different types of high-density, single-shank, planar silicon probes from anesthetized rats were analyzed. Wideband data were filtered to extract spiking activity, then the amplitude distribution of samples and quantitative properties of the recorded brain activity (single unit yield, spike amplitude and isolation distance) were compared between sites located at different positions of the silicon shank, focusing particularly on edge and center sites. Edge sites outperformed center sites: for all five probe types there was a significant difference in the signal power computed from the amplitude distributions, and edge sites recorded significantly more large amplitude samples both in the positive and negative range. Although the single unit yield was similar between site positions, the difference in spike amplitudes was noticeable in the range corresponding to high-amplitude spikes. Furthermore, the advantage of edge sites slightly decreased with decreasing shank width. Our results might aid the design of novel neural implants in enhancing their recording performance by identifying more efficient recording site placements.

scholarly journals Spectroscopic Studies of Laser-Based Far-Ultraviolet Plasma Light Source

2021 ◽  
Vol 11 (15) ◽  
pp. 6919
Author(s):  
Majid Masnavi ◽  
Martin Richardson
Keyword(s):  
Dense Plasma ◽  
Wavelength Region ◽  
Spectroscopic Studies ◽  
Radiation Hydrodynamics ◽  
Full Width ◽  
Half Maximum ◽  
Laser Plasmas ◽  
Series Of Experiments ◽  
Far Ultraviolet ◽  
Radiation Conversion

A series of experiments is described which were conducted to measure the absolute spectral irradiances of laser plasmas created from metal targets over the wavelength region of 123–164 nm by two separate 1.0 μm lasers, i.e., using 100 Hz, 10 ns, 2–20 kHz, 60–100 ns full-width-at-half-maximum pulses. A maximum radiation conversion efficiency of ≈ 3%/2πsr is measured over a wavelength region from ≈ 125 to 160 nm. A developed collisional-radiative solver and radiation-hydrodynamics simulations in comparison to the spectra detected by the Seya–Namioka-type monochromator reveal the strong broadband experimental radiations which mainly originate from bound–bound transitions of low-ionized charges superimposed on a strong continuum from a dense plasma with an electron temperature of less than 10 eV.

scholarly journals Time to peak and full width at half maximum in MR perfusion: valuable indicators for monitoring moyamoya patients after revascularization

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Adam Huang ◽  
Chung-Wei Lee ◽  
Hon-Man Liu
Keyword(s):  
Study Data ◽  
Unknown Etiology ◽  
Dynamic Susceptibility ◽  
Full Width ◽  
Half Maximum ◽  
Mr Perfusion ◽  
Dynamic Susceptibility Contrast ◽  
Time To Peak ◽  
Mr Perfusion Imaging ◽  
Outcome Monitoring

AbstractMoyamoya disease (MMD) is a chronic, steno-occlusive cerebrovascular disorder of unknown etiology. Surgical treatment is the only known effective method to restore blood flow to affected areas of the brain. However, there are lack of generally accepted noninvasive tools for therapeutic outcome monitoring. As dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI) is the standard MR perfusion imaging technique in the clinical setting, we investigated a dataset of nineteen pediatric MMD patients with one preoperational and multiple periodic DSC MRI examinations for four to thirty-eight months after indirect revascularization. A rigid gamma variate model was used to derive two nondeconvolution-based perfusion parameters: time to peak (TTP) and full width at half maximum (FWHM) for monitoring transitional bolus delay and dispersion changes respectively. TTP and FWHM values were normalized to the cerebellum. Here, we report that 74% (14/19) of patients improve in both TTP and FWHM measurements, and whereof 57% (8/14) improve more noticeably on FWHM. TTP is in good agreement with Tmax in estimating bolus delay. Our study data also suggest bolus dispersion estimated by FWHM is an additional, informative indicator in pediatric MMD monitoring.

Preparation of highly c-axis oriented AlN thin films on Hastelloy tapes with Y2O3 buffer layer for flexible SAW sensor applications

2016 ◽  
Vol 09 (02) ◽  
pp. 1650023 ◽  
Author(s):  
Bin Peng ◽  
Jianying Jiang ◽  
Guo Chen ◽  
Lin Shu ◽  
Jie Feng ◽  
...  
Keyword(s):  
Buffer Layer ◽  
Smooth Surface ◽  
Piezoelectric Coefficient ◽  
Piezoelectric Properties ◽  
Mean Square ◽  
Full Width ◽  
Half Maximum ◽  
Sensor Applications ◽  
Saw Sensor ◽  
Y2o3 Buffer Layer

Highly c-axis oriented aluminum nitrade (AlN) films were successfully deposited on flexible Hastelloy tapes by middle-frequency magnetron sputtering. The microstructure and piezoelectric properties of the AlN films were investigated. The results show that the AlN films deposited directly on the bare Hastelloy substrate have rough surface with root mean square (RMS) roughness of 32.43[Formula: see text]nm and its full width at half maximum (FWHM) of the AlN (0002) peak is [Formula: see text]. However, the AlN films deposited on the Hastelloy substrate with Y2O3 buffer layer show smooth surface with RMS roughness of 5.46[Formula: see text]nm and its FWHM of the AlN (0002) peak is only [Formula: see text]. The piezoelectric coefficient d[Formula: see text] of the AlN films deposited on the Y2O3/Hastelloy substrate is larger than three times that of the AlN films deposited on the bare Hastelloy substrate. The prepared highly c-axis oriented AlN films can be used to develop high-temperature flexible SAW sensors.

scholarly journals Research of the anti-resonance pulse forming network and its application in the Marx generator

2016 ◽  
Vol 34 (4) ◽  
pp. 675-686 ◽  
Author(s):  
Z.-L. Pan ◽  
J.-H. Yang ◽  
X.-B. Cheng
Keyword(s):  
Equivalent Circuit ◽  
Rise Time ◽  
Pulse Width ◽  
Marx Generator ◽  
Full Width ◽  
Half Maximum ◽  
Compact Structure ◽  
Fall Time ◽  
Pulse Forming Network ◽  
Load Pulse

AbstractAn anti-resonance pulse forming network (PFN) has been designed, analyzed, and tested for its application in generating quasi-square pulses. According to the circuit simulations, a compact generator based on two/three-section network was constructed. Two-section network is applied in the generator due to its compact structure, while three-section network is employed for generating pulses with higher quality. When two-section network is applied in the generator, the full-width at half-maximum of the load pulse is 400 ns, at the same time, its rise time, flat top and fall time are 90, 180 and 217 ns, respectively. When the three-section network is applied with the same pulse width of the load pulse, the rise time of the output decreases to 60 ns, while the flat top increases to 240 ns and the fall time reduces to 109 ns. Meanwhile, this kind of network could be used to shape the output pulses of generators whose equivalent circuit is LC series discharge network, such as MARX generator, into quasi-square pulses. And the preliminary experiment demonstrates that anti-resonance network could work well on four-stage Marx generators. A sine pulse generated by the four-stage Marx generator is shaped into a quasi-square pulse with voltage of 11.8 kV and pulse width about 110 ns based on two-section anti-resonance network.

Photoluminescence of Erbium-Diffused Silicon

1996 ◽  
Vol 422 ◽  
Author(s):  
H. Horiguchi ◽  
T. Kinone ◽  
R. Saito ◽  
T. Kimura ◽  
T. Ikoma
Keyword(s):  
Room Temperature ◽  
Crystalline Silicon ◽  
Luminescence Spectra ◽  
Main Peak ◽  
Silicon Substrates ◽  
Annealing Atmosphere ◽  
Full Width ◽  
Half Maximum ◽  
Strong Luminescence ◽  
Fine Structures

AbstractErbium films are evaporated on crystalline silicon substrates and are thermally diffused into silicon in an Ar+02 or H2 flow. Very sharp Er3+-related luminescence peaks are observed around 1.54 μ m.The main peak as well as the fine structures of the luminescence spectra depend on the annealing atmosphere, suggesting different luminescence centers. The full width at half maximum (FWHM) of the main peaks is ≤ 0.5nm at 20K. Thermal diffusion with Al films on top of the Er films is found to increase the intensity of the Er3+-related peaks greatly. The temperature dependence between 20 K and room temperature is relatively small, and a strong luminescence is obtained at room temperature.

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