Research

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9 pages, 2976 KiB

Open AccessArticle

Transferability of Diffractive Structure in the Compression Molding of Chalcogenide Glass

by Byeong-Rea Son, Ji-Kwan Kim, Young-Soo Choi and Changsin Park

Micromachines 2023, 14(2), 273; https://doi.org/10.3390/mi14020273 - 20 Jan 2023

Cited by 1 | Viewed by 867

This study investigates the use of Ge₂₈Sb₁₂Se₆₀ chalcogenide glass for the compression molding of an infrared optical lens with a diffractive structure. Firstly, a mold core was prepared through ultra-precision grinding of tungsten carbide, and a chalcogenide glass [...] Read more.

This study investigates the use of Ge₂₈Sb₁₂Se₆₀ chalcogenide glass for the compression molding of an infrared optical lens with a diffractive structure. Firstly, a mold core was prepared through ultra-precision grinding of tungsten carbide, and a chalcogenide glass preform was crafted through a polishing process and designed with a radius that would prevent gas isolation during the molding process. The test lens was then molded at various temperature conditions using the prepared mold core and preform. The diffractive structures of both the mold core and the resulting molded lens were analyzed using a microscope and white light interferometer. The comparison of these diffractive structures revealed that the molding temperature had an effect on the transferability of the diffractive structure during the molding of the chalcogenide glass lens. Furthermore, it was determined that, when the molding temperature was properly adjusted, the diffractive structure of the core could be fully transferred to the surface of the chalcogenide lens. Optimized chalcogenide glass-based lenses have the potential to serve as cost-effective yet high-performance IR optics. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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16 pages, 2957 KiB

Open AccessArticle

Nonparaxial Propagation of Bessel Correlated Vortex Beams in Free Space

by Nikolai I. Petrov

Micromachines 2023, 14(1), 38; https://doi.org/10.3390/mi14010038 - 23 Dec 2022

Cited by 3 | Viewed by 1122

Abstract

The nonparaxial propagation of partially coherent beams carrying vortices in free space is investigated using the method of decomposition of the incident field into coherent diffraction-free modes. Modified Bessel correlated vortex beams with the wavefront curvature are introduced. Analytical expressions are presented to [...] Read more.

The nonparaxial propagation of partially coherent beams carrying vortices in free space is investigated using the method of decomposition of the incident field into coherent diffraction-free modes. Modified Bessel correlated vortex beams with the wavefront curvature are introduced. Analytical expressions are presented to describe the intensity distribution and the degree of coherence at different distances. The evolution of the intensity distribution during beam propagation for various source parameters is analyzed. The effects of nonparaxiality in the propagation of tightly focused coherent vortex beams are analyzed. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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12 pages, 2119 KiB

Open AccessArticle

Dividing the Topological Charge of a Laguerre–Gaussian Beam by 2 Using an Off-Axis Gaussian Beam

by Alexey A. Kovalev, Victor V. Kotlyar, Elena S. Kozlova and Muhammad Ali Butt

Micromachines 2022, 13(10), 1709; https://doi.org/10.3390/mi13101709 - 11 Oct 2022

Cited by 1 | Viewed by 1268

Abstract

In optical computing machines, many parameters of light beams can be used as data carriers. If the data are carried by optical vortices, the information can be encoded by the vortex topological charge (TC). Thus, some optical mechanisms are needed for performing typical [...] Read more.

In optical computing machines, many parameters of light beams can be used as data carriers. If the data are carried by optical vortices, the information can be encoded by the vortex topological charge (TC). Thus, some optical mechanisms are needed for performing typical arithmetic operations with topological charges. Here, we investigate the superposition of a single-ringed (zero-radial-index) Laguerre–Gaussian (LG) beam with an off-axis Gaussian beam in the waist plane. Analytically, we derive at which polar angles intensity nulls can be located and define orders of the optical vortices born around these nulls. We also reveal which of the vortices contribute to the total TC of the superposition and which are compensated for by the opposite-sign vortices. If the LG beam has a TC of m, TC of the superposition is analytically shown to equal [m/2] or [m/2] + 1, where [] means an integer part of the fractional number. Thus, we show that the integer division of the TC by two can be done by superposing the LG beam with an off-axis Gaussian beam. Potential application areas are in optical computing machines and optical data transmission. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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11 pages, 5219 KiB

Open AccessArticle

Tuning Axial Resolution Independent of Lateral Resolution in a Computational Imaging System Using Bessel Speckles

by Vijayakumar Anand

Micromachines 2022, 13(8), 1347; https://doi.org/10.3390/mi13081347 - 19 Aug 2022

Cited by 10 | Viewed by 1646

Abstract

Speckle patterns are formed by random interferences of mutually coherent beams. While speckles are often considered as unwanted noise in many areas, they also formed the foundation for the development of numerous speckle-based imaging, holography, and sensing technologies. In the recent years, artificial [...] Read more.

Speckle patterns are formed by random interferences of mutually coherent beams. While speckles are often considered as unwanted noise in many areas, they also formed the foundation for the development of numerous speckle-based imaging, holography, and sensing technologies. In the recent years, artificial speckle patterns have been generated with spatially incoherent sources using static and dynamic optical modulators for advanced imaging applications. In this report, a basic study has been carried out with Bessel distribution as the fundamental building block of the speckle pattern (i.e., speckle patterns formed by randomly interfering Bessel beams). In general, Bessel beams have a long focal depth, which in this scenario is counteracted by the increase in randomness enabling tunability of the axial resolution. As a direct imaging method could not be applied when there is more than one Bessel beam, an indirect computational imaging framework has been applied to study the imaging characteristics. This computational imaging process consists of three steps. In the first step, the point spread function (PSF) is calculated, which is the speckle pattern formed by the random interferences of Bessel beams. In the next step, the intensity distribution for an object is obtained by a convolution between the PSF and object function. The object information is reconstructed by processing the PSF and the object intensity distribution using non-linear reconstruction. In the computational imaging framework, the lateral resolution remained a constant, while the axial resolution improved when the randomness in the system was increased. Three-dimensional computational imaging with statistical averaging for different cases of randomness has been synthetically demonstrated for two test objects located at two different distances. The presented study will lead to a new generation of incoherent imaging technologies. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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17 pages, 7963 KiB

Open AccessArticle

Spin-Orbital Conversion with the Tight Focus of an Axial Superposition of a High-Order Cylindrical Vector Beam and a Beam with Linear Polarization

by Victor Kotlyar, Sergey Stafeev, Vladislav Zaitsev and Elena Kozlova

Micromachines 2022, 13(7), 1112; https://doi.org/10.3390/mi13071112 - 15 Jul 2022

Cited by 7 | Viewed by 1345

Abstract

In this paper, spin-orbital conversion in the tight focus of an axial superposition of a high-order (order m) cylindrical vector beam and a beam with linear polarization is theoretically and numerically considered. Although such a beam does not have a spin angular [...] Read more.

In this paper, spin-orbital conversion in the tight focus of an axial superposition of a high-order (order m) cylindrical vector beam and a beam with linear polarization is theoretically and numerically considered. Although such a beam does not have a spin angular momentum in the initial plane and the third projection of its Stokes vector is equal to zero, subwavelength local regions with a transverse vortex energy flow and with the non-zero third Stokes projection (the longitudinal component of the spin angular momentum) are formed in the focal plane for an odd number m. This means that such a beam with an odd m has regions of elliptical or circular polarization with alternating directions of rotation (clockwise and counterclockwise) in the focus. For an even m, the field is linearly polarized at every point of the focal plane, and the transverse energy flux is absent. These beams can be used to create a micromachine in which two microparticles in the form of gears are captured in the focus of the beam into neighboring local areas in which the energy flow rotates in different directions, and therefore, these gears will also rotate in different directions. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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11 pages, 3983 KiB

Open AccessArticle

Propagation Characteristics of Circular Airy Vortex Beams in a Uniaxial Crystal along the Optical Axis

by Guoliang Zheng, Qingyang Wu, Tiefeng He and Xuhui Zhang

Micromachines 2022, 13(7), 1006; https://doi.org/10.3390/mi13071006 - 26 Jun 2022

Cited by 5 | Viewed by 1327

Abstract

Circular airy vortex beams (CAVBs) have attracted much attention due to their “abruptly autofocusing” effect, phase singularity, and their potential applications in optical micromanipulation, communication, etc. In this paper, we numerically investigated the propagation properties of circular airy beams (CABs) imposed with different [...] Read more.

Circular airy vortex beams (CAVBs) have attracted much attention due to their “abruptly autofocusing” effect, phase singularity, and their potential applications in optical micromanipulation, communication, etc. In this paper, we numerically investigated the propagation properties of circular airy beams (CABs) imposed with different optical vortices (OVs) along the optical axis of a uniaxial crystal for the first time. Like other common beams, a left-hand circular polarized (LHCP) CAVB, propagating along the optical axis in a uniaxial crystal, can excite a right-hand circular polarized (RHCP) component superimposed with an on-axis vortex of topological charge (TC) number of 2. When the incident beam is an LHCP CAB imposed with an on-axis vortex of TC number of l = 1, both of the two components have an axisymmetric intensity distribution during propagation and form hollow beams near the focal plane because of the phase singularity. The phase pattern shows that the LHCP component carries an on-axis vortex of TC number of l = 1, while the RHCP component carries an on-axis vortex of TC number of l = 3. With a larger TC number (l = 3), the RHCP component has a larger hollow region in the focal plane compared to the LHCP component. We also studied cases of CABs imposed with one and two off-axis OVs. The off-axis OV makes the CAVB’s profile remain asymmetric throughout the propagation. As the propagation distance increases, the off-axis OVs move near the center of the beam and overlap, resulting in a special intensity and phase distribution near the focal plane. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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22 pages, 5717 KiB

Open AccessArticle

Optical Force and Torque on a Graphene-Coated Gold Nanosphere by a Vector Bessel Beam

by Bing Yan, Xiulan Ling, Renxian Li, Jianyong Zhang and Chenhua Liu

Micromachines 2022, 13(3), 456; https://doi.org/10.3390/mi13030456 - 17 Mar 2022

Viewed by 1696

Abstract

In the framework of the generalized Lorenz–Mie theory (GLMT), the optical force and torque on a graphene-coated gold nanosphere by a vector Bessel beam are investigated. The core of the particle is gold, whose dielectric function is given by the Drude–Sommerfeld model, and [...] Read more.

In the framework of the generalized Lorenz–Mie theory (GLMT), the optical force and torque on a graphene-coated gold nanosphere by a vector Bessel beam are investigated. The core of the particle is gold, whose dielectric function is given by the Drude–Sommerfeld model, and the coating is multilayer graphene with layer number N, whose dielectric function is described by the Lorentz–Drude model. The axial optical force

F_{z}

and torque

T_{z}

are numerically analyzed, and the effects of the layer number N, wavelength

λ

, and beam parameters (half-cone angle

α_{0}

, polarization, and order l) are mainly discussed. Numerical results show that the optical force and torque peaks can be adjusted by increasing the thickness of the graphene coating, and can not be adjusted by changing

α_{0}

and l. However,

α_{0}

and l can change the magnitude of the optical force and torque. The numerical results have potential applications involving the trapped graphene-coated gold nanosphere. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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17 pages, 9923 KiB

Open AccessArticle

Theoretical Analysis of Airy–Gauss Bullets Obtained by Means of High Aperture Binary Micro Zonal Plate

by Salvador Blaya, Edmundo Lopez-Sola, Pablo Acebal and Luis Carretero

Micromachines 2022, 13(2), 279; https://doi.org/10.3390/mi13020279 - 10 Feb 2022

Viewed by 1359

Abstract

We theoretically analyze the methodology for obtaining vectorial three-dimensional bullets, concretely Airy–Gauss bullets. To do this, binary micro zonal plates (BZP) were designed in order to obtain different Airy–Gauss bullets with sub-diffraction main lobe width. Following the vectorial diffraction theory, among the electrical [...] Read more.

We theoretically analyze the methodology for obtaining vectorial three-dimensional bullets, concretely Airy–Gauss bullets. To do this, binary micro zonal plates (BZP) were designed in order to obtain different Airy–Gauss bullets with sub-diffraction main lobe width. Following the vectorial diffraction theory, among the electrical field, we extend the theory to the magnetic field, and thus we analyze several properties such as the Poynting vector and the energy of Airy–Gauss vectorial bullets generated by illuminating the designed BZP with a temporal Gaussian circular polarized pulses. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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20 pages, 5288 KiB

Open AccessArticle

Micro-Hole Generation by High-Energy Pulsed Bessel Beams in Different Transparent Materials

by Valeria V. Belloni, Monica Bollani, Shane M. Eaton, Paolo Di Trapani and Ottavia Jedrkiewicz

Micromachines 2021, 12(4), 455; https://doi.org/10.3390/mi12040455 - 18 Apr 2021

Cited by 9 | Viewed by 2728

Abstract

Micro-drilling transparent dielectric materials by using non-diffracting beams impinging orthogonally to the sample can be performed without scanning the beam position along the sample thickness. In this work, the laser micromachining process, based on the combination of picosecond pulsed Bessel beams with the [...] Read more.

Micro-drilling transparent dielectric materials by using non-diffracting beams impinging orthogonally to the sample can be performed without scanning the beam position along the sample thickness. In this work, the laser micromachining process, based on the combination of picosecond pulsed Bessel beams with the trepanning technique, is applied to different transparent materials. We show the possibility to create through-apertures with diameter on the order of tens of micrometers, on dielectric samples with different thermal and mechanical characteristics as well as different thicknesses ranging from two hundred to five hundred micrometers. Advantages and drawbacks of the application of this technique to different materials such as glass, polymer, or diamond are highlighted by analyzing the features, the morphology, and the aspect-ratio of the through-holes generated. Alternative Bessel beam drilling configurations, and the possibility of optimization of the quality of the aperture at the output sample/air interface is also discussed in the case of glass. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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12 pages, 16877 KiB

Open AccessArticle

Generation of Complex Transverse Energy Flow Distributions with Autofocusing Optical Vortex Beams

by Svetlana N. Khonina, Alexey P. Porfirev, Andrey V. Ustinov and Muhammad Ali Butt

Micromachines 2021, 12(3), 297; https://doi.org/10.3390/mi12030297 - 12 Mar 2021

Cited by 14 | Viewed by 2249

Abstract

Optical vortex (OV) beams are widely used for the generation of light fields with transverse energy flow inducing orbital motion of the nano- and microparticles in the transverse plane. Here, we present some new modifications of OV beams with autofocusing properties for shaping [...] Read more.

Optical vortex (OV) beams are widely used for the generation of light fields with transverse energy flow inducing orbital motion of the nano- and microparticles in the transverse plane. Here, we present some new modifications of OV beams with autofocusing properties for shaping complex transverse energy flow distributions varying in space. The angular component of the complex amplitude of these beams is defined by the superpositions of OV beams with different topological charges. The proposed approach provides a convenient method to control the three-dimensional structure of the generated autofocusing OV beams. The control of the transverse distribution of an autofocusing beam provides a wide variety of generated fields with both rotating and periodic properties, which can be used in the field of laser manipulation and laser material processing. Thus, the obtained numerical results predict different types of motion of the trapped particles for the designed OV autofocusing beams. The experimental results agree with modeling results and demonstrate the principal possibility to shape such laser beams using spatial light modulators. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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Review

Jump to: Research

16 pages, 3135 KiB

Open AccessReview

Bessel Beams in Ophthalmology: A Review

by C. S. Suchand Sandeep, Ahmad Khairyanto, Tin Aung and Murukeshan Vadakke Matham

Micromachines 2023, 14(9), 1672; https://doi.org/10.3390/mi14091672 - 27 Aug 2023

Cited by 1 | Viewed by 1365

Abstract

The achievable resolution of a conventional imaging system is inevitably limited due to diffraction. Dealing with precise imaging in scattering media, such as in the case of biomedical imaging, is even more difficult owing to the weak signal-to-noise ratios. Recent developments in non-diffractive [...] Read more.

The achievable resolution of a conventional imaging system is inevitably limited due to diffraction. Dealing with precise imaging in scattering media, such as in the case of biomedical imaging, is even more difficult owing to the weak signal-to-noise ratios. Recent developments in non-diffractive beams such as Bessel beams, Airy beams, vortex beams, and Mathieu beams have paved the way to tackle some of these challenges. This review specifically focuses on non-diffractive Bessel beams for ophthalmological applications. The theoretical foundation of the non-diffractive Bessel beam is discussed first followed by a review of various ophthalmological applications utilizing Bessel beams. The advantages and disadvantages of these techniques in comparison to those of existing state-of-the-art ophthalmological systems are discussed. The review concludes with an overview of the current developments and the future perspectives of non-diffractive beams in ophthalmology. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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27 pages, 54393 KiB

Open AccessReview

Bessel Beam: Significance and Applications—A Progressive Review

by Svetlana Nikolaevna Khonina, Nikolay Lvovich Kazanskiy, Sergey Vladimirovich Karpeev and Muhammad Ali Butt

Micromachines 2020, 11(11), 997; https://doi.org/10.3390/mi11110997 - 11 Nov 2020

Cited by 106 | Viewed by 12575

Abstract

Diffraction is a phenomenon related to the wave nature of light and arises when a propagating wave comes across an obstacle. Consequently, the wave can be transformed in amplitude or phase and diffraction occurs. Those parts of the wavefront avoiding an obstacle form [...] Read more.

Diffraction is a phenomenon related to the wave nature of light and arises when a propagating wave comes across an obstacle. Consequently, the wave can be transformed in amplitude or phase and diffraction occurs. Those parts of the wavefront avoiding an obstacle form a diffraction pattern after interfering with each other. In this review paper, we have discussed the topic of non-diffractive beams, explicitly Bessel beams. Such beams provide some resistance to diffraction and hence are hypothetically a phenomenal alternate to Gaussian beams in several circumstances. Several outstanding applications are coined to Bessel beams and have been employed in commercial applications. We have discussed several hot applications based on these magnificent beams such as optical trapping, material processing, free-space long-distance self-healing beams, optical coherence tomography, superresolution, sharp focusing, polarization transformation, increased depth of focus, birefringence detection based on astigmatic transformed BB and encryption in optical communication. According to our knowledge, each topic presented in this review is justifiably explained. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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