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.

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.

Comparative Study of Some Fiber-Optic Remote Raman Probe Designs. Part II: Tests of Single-Fiber, Lensed, and Flat- and Bevel-Tip Multi-Fiber Probes

1996 ◽  
Vol 50 (7) ◽  
pp. 849-860 ◽  
Author(s):  
Thomas F. Cooney ◽  
H. Trey Skinner ◽  
S. M. Angel
Keyword(s):  
Fiber Optic ◽  
Focal Point ◽  
Focal Length ◽  
Numerical Aperture ◽  
Optical Filters ◽  
Organic Liquids ◽  
Raman Signal ◽  
Immersion Medium ◽  
Lens Focal Length ◽  
Overlap Model

We compare relative performances of flat-tipped, beveled (two-fiber and six-around-one), and single-lensed focused fiber-optic Raman probes and, where feasible, evaluate the utility of optical filters for reducing fiber background. The sensitivity profile of each probe is determined by measuring the relative intensity of light backscattered off a flat surface as a function of distance from the probe tip. The experimental results are compared with a simple light-cone-overlap model incorporating fiber numerical aperture, fiber and immersion medium refractive indices, separation between excitation and collection fibers, number of fibers, and fiber bevel angle and/or lens focal length. The model and sensitivity profiles are used to interpret the sampling regions for Raman spectra obtained by using each of the probes with a clear, transparent sample (single-crystal sparry calcite), a white, partially transparent sample (acetaminophen tablet), and a set of organic liquids of varying refractive index. The sensitivity of the tested commercial lensed probe drops off symmetrically about the focal point. For both solid samples, the intensity of fiber background follows a profile determined primarily by laser backscattering off the surface, whereas the sample Raman signal follows a profile dependent upon sampling depth.

Using GPUs for Realtime Prediction of Optical Forces on Microsphere Ensembles

2012 ◽  
Author(s):  
Sujal Bista ◽  
Sagar Chowdhury ◽  
Satyandra K. Gupta ◽  
Amitabh Varshney
Keyword(s):  
Laser Beam ◽  
Optical Tweezers ◽  
Computational Models ◽  
Laser Beams ◽  
Cell Manipulation ◽  
Optical Traps ◽  
Optical Forces ◽  
Gaussian Laser Beam ◽  
Multiple Particles ◽  
Speed Up

Laser beams can be used to create optical traps that can hold and transport small particles. Optical trapping has been used in a number of applications ranging from prototyping at the microscale to biological cell manipulation. Successfully using optical tweezers requires predicting optical forces on the particle being trapped and transported. Reasonably accurate theory and computational models exist for predicting optical forces on a single particle in the close vicinity of a Gaussian laser beam. However, in practice the workspace includes multiple particles that are manipulated using individual optical traps. It has been experimentally shown that the presence of a particle can cast a shadow on a nearby particle and hence affect the optical forces acting on it. Computing optical forces in the presence of shadows in real-time is not feasible on CPUs. In this paper, we introduce a ray-tracing-based application optimized for GPUs to calculate forces exerted by the laser beams on microparticle ensembles in an optical tweezers system. When evaluating the force exerted by a laser beam on 32 interacting particles, our GPU-based application is able to get a 66-fold speed up compared to a single core CPU implementation of traditional Ashkin’s approach and a 10-fold speedup over its single core CPU-based counterpart.

3D Microscopy using Confocal Microscopy

1996 ◽  
Vol 54 ◽  
pp. 270-271
Author(s):  
Ernst H. K. Stelzer ◽  
Steffen Lindek
Keyword(s):  
Incident Light ◽  
Three Dimensional ◽  
Numerical Aperture ◽  
Biological Research ◽  
Half Maximum ◽  
Optical Sectioning ◽  
Observation Volume ◽  
Spread Function ◽  
Relationship Of ◽  
The Relationship

The importance of confocal fluorescence microscopy in modem biological research results from its optical sectioning capability, which allows the three-dimensional analysis of thick specimens. This property is due to the combination of a point-like light source and a point-like detector, which restrict the illumination and detection volumes, respectively. Only the volume that is illuminated and detected is relevant to the confocal observation volume. The smaller it is, the better is the resolution. The performance of a confocal microscope is thus primarily specified by the spatial extent of the confocal point spread function (PSF). The extent can be estimated, e.g., by the volume enclosed by the isosurface at half maximum of the PSF (VHM – volume at half maximum).The relationship of the parameters that determine the lateral resolution of a microscope has been described by Ernst Abbé. The diameter of a light spot in the focal plane Δx is proportional to the wavelength λ of the incident light and inversely proportional to the numerical aperture of the optical system (N.A. = n, ∙ sin α).

Sample Preparation for High Numerical Aperture Solid Immersion Lens Laser Imaging

2014 ◽  
Author(s):  
M.S. Wei ◽  
H.B. Chong ◽  
S.H. Lim ◽  
C. Richardson
Keyword(s):  
Sample Preparation ◽  
Focal Length ◽  
Numerical Aperture ◽  
Fault Isolation ◽  
Numerical Control ◽  
Thickness Variation ◽  
Solid Immersion Lens ◽  
Laser Imaging ◽  
High Numerical Aperture ◽  
Silicon Thickness

Abstract High resolution laser imaging, using high numerical aperture (NA) solid immersion lens (SIL) for backside fault isolation imposes stringent sample preparation requirements; as a result of the short focal length of SIL, a die must be thinned to a targeted thickness with less than a ±5 μm silicon thickness variation across the entire die. Flip chip packaged dice suffer from warpage due to various package sizes and substrate thicknesses. Such broad spectrums of part geometries pose a great challenge to meet such silicon planarity requirements. As relaxation of the packaged silicon during polishing causes the warpage profile to change dynamically and unpredictably throughout the thinning process, it has become an added challenge to meet the stringent sample preparation requirements. To overcome the stochastic nature of this problem, a two-step polishing recipe consisting of computer numerical control (CNC) mechanical milling and polishing processes has been developed to achieve sufficient silicon thickness uniformity to enable SIL imaging across an entire silicon chip as large as approximately 20 mm x 15 mm.

Planar plasmonic lens based on circular nanohole in a gold film in visible light range

2019 ◽  
Vol 33 (06) ◽  
pp. 1950069 ◽  
Author(s):  
Fang Chen ◽  
Lihui Sun ◽  
Huafeng Zhang ◽  
Jijun Li ◽  
Chunchao Yu
Keyword(s):  
Full Width Half Maximum ◽  
Gold Film ◽  
Focal Point ◽  
Focal Length ◽  
Fdtd Simulation ◽  
Plasmonic Lens ◽  
Planar Lens ◽  
Sommerfeld Integral ◽  
Visible Light Range ◽  
Optical Integration

Plasmonic planar lens consisting of circular nanohole etched on the gold film have been investigated, the proposed plamonic lens was immersed in a high index medium to improve the focusing efficiency. The focal length and the full-width half-maximum beams width of the focal point were calculated in detail. The focal length calculated by FDTD simulation agrees well with Rayleigh–Sommerfeld integral. Moreover, the proposed lens structure is polarization-independent since circularly symmetric. The easy fabricate structure and excellent focusing performance of this plasmonic lens will open new avenues for optical storage and optical integration.

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 Phase characterisation of metalenses

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Maoxiong Zhao ◽  
Mu Ku Chen ◽  
Ze-Peng Zhuang ◽  
Yiwen Zhang ◽  
Ang Chen ◽  
...  
Keyword(s):  
Measurement System ◽  
Phase Distribution ◽  
Phase Measurement ◽  
Berry Phase ◽  
Focal Length ◽  
Numerical Aperture ◽  
Superior Performance ◽  
Distribution Analysis ◽  
Interferometric Imaging ◽  
Measured Phase

AbstractMetalenses have emerged as a new optical element or system in recent years, showing superior performance and abundant applications. However, the phase distribution of a metalens has not been measured directly up to now, hindering further quantitative evaluation of its performance. We have developed an interferometric imaging phase measurement system to measure the phase distribution of a metalens by taking only one photo of the interference pattern. Based on the measured phase distribution, we analyse the negative chromatic aberration effect of monochromatic metalenses and propose a feature size of metalenses. Different sensitivities of the phase response to wavelength between the Pancharatnam-Berry phase-based metalens and propagation phase-reliant metalens are directly observed in the experiment. Furthermore, through phase distribution analysis, it is found that the distance between the measured metalens and the brightest spot of focusing will deviate from the focal length when the metalens has a low nominal numerical aperture, even though the metalens is ideal without any fabrication error. We also use the measured phase distribution to quantitatively characterise the imaging performance of the metalens. Our phase measurement system will help not only designers optimise the designs of metalenses but also fabricants distinguish defects to improve the fabrication process, which will pave the way for metalenses in industrial applications.

scholarly journals Phase-Controlled Planar Metalenses for High-Resolution Terahertz Focusing

Photonics ◽  
2021 ◽  
Vol 8 (5) ◽  
pp. 143
Author(s):  
Xin Yu ◽  
Yun Shen ◽  
Guohong Dai ◽  
Liner Zou ◽  
Tailin Zhang ◽  
...  
Keyword(s):  
High Resolution ◽  
Spatial Resolution ◽  
Imaging System ◽  
Incident Light ◽  
Near Field ◽  
Numerical Aperture ◽  
Full Width ◽  
Half Maximum ◽  
Near Field Imaging ◽  
Field Imaging

We experimentally demonstrate that high-resolution terahertz focusing can be realized in planar metalenses, which consist of arrays of different V-shaped antenna units on a silicon substrate. Numerical results show that a larger numerical aperture of metalenses can provide smaller full width at half maximum of field distribution, leading to higher spatial resolution. The measurement of fabricated metalenses samples was performed by a terahertz near-field imaging system, and experimental results agree well with the numerical prediction. Especially for 1.1 THz incident light, when the numerical aperture increases from 0.79 to 0.95, the full width at half maximum correspondingly decreases from 343 μm to 206 μm, offering an improvement of spatial resolution.

scholarly journals High numerical aperture metalens to generate an energy backflow

2020 ◽  
Vol 44 (5) ◽  
pp. 691-698
Author(s):  
V.V. Kotlyar ◽  
S.S. Stafeev ◽  
L. O'Faolain ◽  
M.V. Kotlyar
Keyword(s):  
Focal Length ◽  
Ion Beam ◽  
Near Field ◽  
Fdtd Method ◽  
Numerical Aperture ◽  
Polarized Light ◽  
Optical Microscope ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Left Handed

Using electronic beam lithography and reactive ion beam etching, a metalens is manufactured in a thin layer of amorphous silicon of a 130-nm depth, a 30-µm diameter, and a 633-nm focal length (equal to the illumination wavelength). The metalens is composed of 16 sectored subwavelength binary gratings with a 220-nm period. The uniqueness of this metalens is that when illuminated by left-handed circularly polarized light, it is capable of generating a left-handed circularly polarized vortex beam with a topological charge of 2, generating a second-order cylindrical vector beam when illuminated by linearly polarized light. Both for linear and circular incident polarization, an energy backflow is found to be generated in the vicinity of the tight focus. Transverse intensity distributions measured with a scanning near-field optical microscope near the focus of the metalens are in qualitative agreement with the intensity distributions calculated by the FDTD method. This confirms that a backward energy flow takes place at the focus of the metalens. A metalens generating an energy backflow near its focus is fabricated and characterized for the first time.

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