Design and fabrication of diffractive phase element for minimizing the focusing spot size beyond diffraction limit

Hyperbolic metamaterials can manipulate electromagnetic waves by converting evanescent waves into propagating waves and thus support light propagation without diffraction limit. In this paper, deep subwavelength focusing (or power concentration) is demonstrated both numerically and experimentally using hyperbolic metamaterials. The results verify that hyperbolic metamaterials can focus a broad collimated beam to spot size of ~λ0/6 using wired medium design for both normal and oblique incidence. The nonmagnetic design, no-cut-off operation, and preferred direction of propagation in these materials significantly reduce the attenuation in electromagnetic waves.

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High efficiency dielectric photonic crystal fiber metalens

Scientific Reports ◽

10.1038/s41598-020-77821-5 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Myunghwan Kim ◽

Soeun Kim

Keyword(s):

Photonic Crystal ◽

Photonic Crystal Fiber ◽

Optical Fibers ◽

High Efficiency ◽

Focal Length ◽

Spot Size ◽

Diffraction Limit ◽

Crystal Fiber ◽

The Core ◽

Light Manipulation

AbstractOptical fibers have been utilized in various fields owing to their superior guiding performance. However, the modification of optical properties and light manipulation in fibers are restricted by the limitation of the core and cladding materials. In addition, the spot size of the light is constrained by the diffraction limit. In this study, we propose an all-dielectric metalens patterned on the facet of a photonic crystal fiber. The metasurface, which contains Si pillars, satisfies the required phase diagram for focusing light with high transmission. The proposed metalens has a focal length of 30 µm and achieves an outstanding efficiency of up to 88% at a wavelength of 1.55 µm, which is approximately 5 times higher than that of a metal-based metalens. We believe that this scheme may pave the way for in-fiber metasurface applications.

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Study of Superoscillating Functions Application to Overcome the Diffraction Limit with Suppressed Sidelobes

Optics ◽

10.3390/opt2030015 ◽

2021 ◽

Vol 2 (3) ◽

pp. 155-168

Author(s):

Svetlana N. Khonina ◽

Ekaterina D. Ponomareva ◽

Muhammad A. Butt

Keyword(s):

Numerical Study ◽

Near Field ◽

Plane Waves ◽

Spot Size ◽

Diffraction Limit ◽

Field Zone ◽

Focal Spot Size ◽

One Dimensional ◽

Spatial Frequencies ◽

Superoscillating Functions

The problem of overcoming the diffraction limit does not have an unambiguously advantageous solution because of the competing nature of different beams’ parameters, such as the focal spot size, energy efficiency, and sidelobe level. The possibility to overcome the diffraction limit with suppressed sidelobes out of the near-field zone using superoscillating functions was investigated in detail. Superoscillation is a phenomenon in which a superposition of harmonic functions contains higher spatial frequencies than any of the terms in the superposition. Two types of superoscillating one-dimensional signals were considered, and simulation of their propagation in the near diffraction zone based on plane waves expansion was performed. A comparative numerical study showed the possibility of overcoming the diffraction limit with a reduced level of sidelobes at a certain distance outside the zone of evanescent waves.

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Intensity of Diffraction of Laser Irradiating a Microparticle in Nanostructure Processing

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.83-86.1282 ◽

2009 ◽

Vol 83-86 ◽

pp. 1282-1287

Author(s):

Ching Yen Ho ◽

Mao Yu Wen ◽

C. Ma

Keyword(s):

Electromagnetic Wave ◽

Near Field ◽

Wave Theory ◽

Spot Size ◽

Diffraction Limit ◽

Materials Processing ◽

Small Aperture ◽

Laser Technology ◽

Field Techniques ◽

20 Nm

Traditional materials processing in the nanometer range using laser technology is very difficult with conventional optics due to the diffraction limit of the beam wavelength, a near-field technology has been developed to circumvent the diffraction limit, permitting the spot size to be reduced down to 20 nm. In most near-field techniques, this technology is achieved by placing a small aperture or microparticle between the sample and the light source. Therefore this paper will analytically investigate the profile of the intensity for diffraction of laser irradiating an aperture or microparticle in nanostructure processing. Classical electromagnetic wave theory is employed to calculate the intensity for diffraction of laser irradiating a microparticle or aperture. The results will reveal the differences between an aperture and micoparticle for diffraction of laser. The effect of laser parameters on the intensity and distribution of diffraction will be also discussed.

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Sharper Focal Spot for a Radially Polarized Beam Using Ring Aperture with Phase Jump

Journal of Engineering ◽

10.1155/2013/512971 ◽

2013 ◽

Vol 2013 ◽

pp. 1-8 ◽

Cited By ~ 3

Author(s):

Svetlana N. Khonina ◽

Andrei V. Ustinov

Keyword(s):

Focal Spot ◽

Central Peak ◽

Spot Size ◽

Diffraction Limit ◽

Destructive Interference ◽

Phase Jump ◽

Radially Polarized Beam ◽

Annular Aperture ◽

Polarized Beam ◽

Radially Polarized

We study analytically and numerically in which way the width of ring aperture containing a phase jump affects the size and intensity of the focal spot generated with a radially polarized beam. It is shown that by means of destructive interference of beams coming from the different-phase rings it becomes possible to overcome the scalar diffraction limit corresponding to the first zero of the zero-order Bessel function. The minimal focal spot size (FWHM=0.33λ) is found to be attained when the annular aperture width amounts to 20% of the full-aperture radius. In this case, the side-lobe intensity is not larger than 30% of the central peak. A wider annular aperture with the phase jump introduced is also shown to form a focal spot not exceeding the diffraction limit for a narrow annular aperture, simultaneously providing a nearly six times higher intensity. In this case, the side lobes amount to 35% of the central peak.

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Remarks on the application of backscattered electron imaging (BEI) to the scanning electron microscopy (SEM) of biological structures

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100076159 ◽

1983 ◽

Vol 41 ◽

pp. 484-487

Author(s):

Etienne de Harven

Keyword(s):

High Resolution ◽

Incident Beam ◽

Spot Size ◽

Primary Electron ◽

Critical Point Drying ◽

Cell Shapes ◽

High Resolution Images ◽

Backscattered Electron ◽

Electron Imaging ◽

Scanning Electron

Biological ultrastructures have been extensively studied with the scanning electron microscope (SEM) for the past 12 years mainly because this instrument offers accurate and reproducible high resolution images of cell shapes, provided the cells are dried in ways which will spare them the damage which would be caused by air drying. This can be achieved by several techniques among which the critical point drying technique of T. Anderson has been, by far, the most reproducibly successful. Many biologists, however, have been interpreting SEM micrographs in terms of an exclusive secondary electron imaging (SEI) process in which the resolution is primarily limited by the spot size of the primary incident beam. in fact, this is not the case since it appears that high resolution, even on uncoated samples, is probably compromised by the emission of secondary electrons of much more complex origin.When an incident primary electron beam interacts with the surface of most biological samples, a large percentage of the electrons penetrate below the surface of the exposed cells.

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A High Resolution Scanning Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100101529 ◽

1968 ◽

Vol 26 ◽

pp. 356-357

Author(s):

A. V. Crewe ◽

J. Wall ◽

L. M. Welter

Keyword(s):

High Resolution ◽

Field Emission ◽

Spherical Aberration ◽

Focal Length ◽

Spot Size ◽

Emission Source ◽

Field Of View ◽

Scanning Microscope ◽

Magnetic Lens ◽

High Quality

A scanning microscope using a field emission source has been described elsewhere. This microscope has now been improved by replacing the single magnetic lens with a high quality lens of the type described by Ruska. This lens has a focal length of 1 mm and a spherical aberration coefficient of 0.5 mm. The final spot size, and therefore the microscope resolution, is limited by the aberration of this lens to about 6 Å.The lens has been constructed very carefully, maintaining a tolerance of + 1 μ on all critical surfaces. The gun is prealigned on the lens to form a compact unit. The only mechanical adjustments are those which control the specimen and the tip positions. The microscope can be used in two modes. With the lens off and the gun focused on the specimen, the resolution is 250 Å over an undistorted field of view of 2 mm. With the lens on,the resolution is 20 Å or better over a field of view of 40 microns. The magnification can be accurately varied by attenuating the raster current.

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Image registration with a computer driven S.T.E.M.

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100107630 ◽

1978 ◽

Vol 36 (1) ◽

pp. 98-99

Author(s):

A.M.H. Schepman ◽

J.A.P. van der Voort ◽

J.E. Mellema

Keyword(s):

Spot Size ◽

Scanning Transmission Electron Microscope ◽

Small Computer ◽

Structural Studies ◽

Area Of Interest ◽

Transmission Electron ◽

Scanning Transmission ◽

Specimen Area ◽

On Line ◽

Minimum Distances

A Scanning Transmission Electron Microscope (STEM) was coupled to a small computer. The system (see Fig. 1) has been built using a Philips EM400, equipped with a scanning attachment and a DEC PDP11/34 computer with 34K memory. The gun (Fig. 2) consists of a continuously renewed tip of radius 0.2 to 0.4 μm of a tungsten wire heated just below its melting point by a focussed laser beam (1). On-line operation procedures were developped aiming at the reduction of the amount of radiation of the specimen area of interest, while selecting the various imaging parameters and upon registration of the information content. Whereas the theoretical limiting spot size is 0.75 nm (2), routine resolution checks showed minimum distances in the order 1.2 to 1.5 nm between corresponding intensity maxima in successive scans. This value is sufficient for structural studies of regular biological material to test the performance of STEM over high resolution CTEM.

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Ultra-spatially resolved synchrotron powered FT-IR microspectroscopy of individual cells of biological material

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100140798 ◽

1995 ◽

Vol 53 ◽

pp. 884-885

Author(s):

David L. Wetzel ◽

John A. Reffner ◽

Gwyn P. Williams

Keyword(s):

Thermal Noise ◽

Spot Size ◽

Acquisition Time ◽

Thermal Source ◽

Signal To Noise ◽

Spatially Resolved ◽

Good Spatial Resolution ◽

Small Spot ◽

Ft Ir ◽

Ir Microspectroscopy

Synchrotron radiation is 100 to 1000 times brighter than a thermal source such as a globar. It is not accompanied with thermal noise and it is highly directional and nondivergent. For these reasons, it is well suited for ultra-spatially resolved FT-IR microspectroscopy. In efforts to attain good spatial resolution in FT-IR microspectroscopy with a thermal source, a considerable fraction of the infrared beam focused onto the specimen is lost when projected remote apertures are used to achieve a small spot size. This is the case because of divergence in the beam from that source. Also the brightness is limited and it is necessary to compromise on the signal-to-noise or to expect a long acquisition time from coadding many scans. A synchrotron powered FT-IR Microspectrometer does not suffer from this effect. Since most of the unaperatured beam’s energy makes it through even a 12 × 12 μm aperture, that is a starting place for aperture dimension reduction.

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Confocal Raman mapping

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100132200 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1514-1515

Author(s):

J. Barbillat ◽

M. Delhaye ◽

P. Dhamelincourt

Keyword(s):

Chemical Species ◽

Diffraction Limit ◽

Microscopic Level ◽

Raman Mapping ◽

Complete Spectrum ◽

Laser Illumination ◽

Ccd Detector ◽

Raman Microprobe ◽

Photodiode Array ◽

Raman Image

Raman mapping, with a spatial resolution close to the diffraction limit, can help to reveal the distribution of chemical species at the surface of an heterogeneous sample.As early as 1975,three methods of sample laser illumination and detector configuration have been proposed to perform Raman mapping at the microscopic level (Fig. 1),:- Point illumination:The basic design of the instrument is a classical Raman microprobe equipped with a PM tube or either a linear photodiode array or a two-dimensional CCD detector. A laser beam is focused on a very small area ,close to the diffraction limit.In order to explore the whole surface of the sample,the specimen is moved sequentially beneath the microscope by means of a motorized XY stage. For each point analyzed, a complete spectrum is obtained from which spectral information of interest is extracted for Raman image reconstruction.- Line illuminationA narrow laser line is focused onto the sample either by a cylindrical lens or by a scanning device and is optically conjugated with the entrance slit of the stigmatic spectrograph.

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