Quasi-achromatic Fresnel zone lens with ring focus.
TL;DR: Experimental results confirm the generation of a wavelength-independent ring pattern at the focus of the rf-FZL, which is found to be quasi-achromatic, in that the diameter is wavelength independent but its location is not.
Abstract: The phase of a standard Fresnel zone lens (FZL) is periodically modulated in the radial direction using the phase of a binary fraxicon. The resulting element (rf-FZL) focuses light into a ring. The ring is found to be quasi-achromatic, in that the diameter is wavelength independent but its location is not. The binary rf-FZL is fabricated using electron beam direct writing. Experimental results confirm the generation of a wavelength-independent ring pattern at the focus of the rf-FZL. An efficiency of 24% was obtained. The variation in radius of ring pattern was reduced from 61 μm to less than 10 nm for a corresponding wavelength variation from 532 to 633 nm.
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TL;DR: This study demonstrates a single camera shot, lensless, interferenceless, motionless, non-scanning, space, spectrum, and time resolved five-dimensional incoherent imaging technique using tailored chaotic waves with quasi-random intensity and phase distributions.
Abstract: Multispectral imaging technology is a valuable scientific tool for various applications in astronomy, remote sensing, molecular fingerprinting, and fluorescence imaging. In this study, we demonstrate a single camera shot, lensless, interferenceless, motionless, non-scanning, space, spectrum, and time resolved five-dimensional incoherent imaging technique using tailored chaotic waves with quasi-random intensity and phase distributions. Chaotic waves can distinctly encode spatial and spectral information of an object in single self-interference intensity distribution. In this study, a tailored chaotic wave with a nearly pure phase function and lowest correlation noise is generated using a quasi-random array of pinholes. A unique sequence of signal processing techniques is applied to extract all possible spatial and spectral channels with the least entropy. The depth-wavelength reciprocity is exploited to see colour from depth and depth from colour and the physics of beam propagation is exploited to see at one depth by calibrating at another.
38 citations
Cites background from "Quasi-achromatic Fresnel zone lens ..."
...Quasi-achromatic lenses with capabilities to change focal distance by changing wavelength wavelength have been investigated [7]....
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TL;DR: In this paper, a comparison of the beam generated by different beam generation and focused ion beam milling methods is presented. And in order to be able to compare methods, specific functions of ring generation and focusing have been added in all cases.
Abstract: Diffractive optics has traditionally been used to transform a parallel beam of light into a pattern with a desired phase and intensity distribution. One of the advantages of using diffractive optics is the fact that multiple functions can be integrated into one element. Although, in theory, several functions can be combined, the efficiency is reduced with each added function. Also, depending on the nature of each function, feature sizes could get finer. Optical lithography with its 1 μm limit becomes inadequate for fabrication and sophisticated tools such as e-beam lithography and focused ion beam milling are required. Two different techniques, namely, a modulo-2π phase addition technique and an analog technique for design and fabrication of composite elements are studied. A comparison of the beams generated in both cases is presented. In order to be able to compare methods, specific functions of ring generation and focusing have been added in all cases.
15 citations
TL;DR: In this article, a binary composite diffractive optical element with the functions of a spiral phase plate (SPP), an axicon, and a Fresnel zone lens (FZL) were designed with different topological charges.
Abstract: Binary composite diffractive optical elements with the functions of a spiral phase plate (SPP), an axicon, and a Fresnel zone lens (FZL) were designed with different topological charges. The element was designed in two steps. In the first step, the function of an SPP was combined with that of an axicon by spiraling the periods of the axicon with respect to the phase of the SPP followed by a modulo- 2π phase addition with the phase of an FZL in the second step. The higher-order Bessel beams generated by the binary phase spiral axicon are superposed at the FZL’s focal plane. Although location of the focal plane is wavelength dependent, the radius of the flower-like beams generated by the element was found to be independent of wavelength. The element was fabricated using electron-beam direct writing. The evaluation results matched well with the simulation results, generating flower-like beams at the focal plane of the FZL.
11 citations
Cites background from "Quasi-achromatic Fresnel zone lens ..."
...Therefore, the increase in diffraction angle of the spiral axicon and the decrease in focal length of the FZL cancel each other out, resulting in a wavelength independent diameter of the flower-like pattern.(33) The wavelength dependency is analyzed for a variation of wavelength by 50 nm for Λ 1⁄4 190 μm....
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...The combination of a binary axicon with a binary FZL enables the wavelength independent ring diameter property.(33) As seen earlier,(33) when the wavelength changes, the diameter of the irradiance profile remains constant although there is a shift in the focal plane position....
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18 Dec 2020
TL;DR: In this paper, a co-axial pump (optical)-probe (x-rays) experimental concept and show performance of the optical component are presented and different realisations of optical pump are discussed.
Abstract: We put forward a co-axial pump (optical)-probe (x-rays) experimental concept and show performance of the optical component. A Bessel beam generator with a central 100 µm diameter hole (on the optical axis) was fabricated using femtosecond (fs) laser structuring inside a silica plate. This flat-axicon optical element produces a needle-like axial intensity distribution which can be used for the optical pump pulse. The fs-x-ray free electron laser (X-FEL) beam of sub-1 µm diameter can be introduced through the central hole along the optical axis onto a target as a probe. Different realisations of optical pump are discussed. Such optical elements facilitate alignment of ultra-short fs-pulses in space and time and can be used in light–matter interaction experiments at extreme energy densities on the surface and in the volume of targets. Full advantage of ultra-short 10 fs-X-FEL probe pulses with fs-pump (optical) opens an unexplored temporal dimension of phase transitions and the fastest laser-induced rates of material heating and quenching. A wider field of applications of fs-laser-enabled structuring of materials and design of specific optical elements for astrophotonics is presented.
10 citations
TL;DR: Nonlinear reconstruction (NLR) as discussed by the authors was developed in 2017 to reconstruct the object image in the case of optical-scattering modulators, which can reconstruct an object image modulated by an axicons, bifocal lenses and even exotic spiral diffractive elements, which generate deterministic optical fields.
Abstract: Indirect-imaging methods involve at least two steps, namely optical recording and computational reconstruction. The optical-recording process uses an optical modulator that transforms the light from the object into a typical intensity distribution. This distribution is numerically processed to reconstruct the object’s image corresponding to different spatial and spectral dimensions. There have been numerous optical-modulation functions and reconstruction methods developed in the past few years for different applications. In most cases, a compatible pair of the optical-modulation function and reconstruction method gives optimal performance. A new reconstruction method, termed nonlinear reconstruction (NLR), was developed in 2017 to reconstruct the object image in the case of optical-scattering modulators. Over the years, it has been revealed that the NLR can reconstruct an object’s image modulated by an axicons, bifocal lenses and even exotic spiral diffractive elements, which generate deterministic optical fields. Apparently, NLR seems to be a universal reconstruction method for indirect imaging. In this review, the performance of NLR isinvestigated for many deterministic and stochastic optical fields. Simulation and experimental results for different cases are presented and discussed.
9 citations
References
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TL;DR: Noncontact cornea trephination was performed on human eye-bank eyes by using a Q-switched Er:YAG laser with a axicon-lens combination to demonstrate the possibility of replacing mechanical trephinations in corneal surgery.
Abstract: A new laser beam delivery system using axicon beam shaping has been designed to produce controllable surface ablation as well as trephination for the corneal surgery. Noncontact cornea trephination was performed on human eye-bank eyes by using a Q-switched Er:YAG laser with a axicon-lens combination. The results shows that the uniformity of the trephination along the ring depends on the radial symmetry of the beam. The histological results of the samples show that the damage zone of the laser cut is less than 10 mu m. This demonstrates the possibility of replacing mechanical trephination in corneal surgery. >
68 citations
TL;DR: In this paper, the design and fabrication of the static and dynamic, on-and off-axis Fresnel zone lenses as well as their optical and switching properties are presented, and the switching behavior of the dynamic lenses is studied.
Abstract: Static and dynamic Fresnel zone lenses were fabricated in quartz glass by means of microstructuring techniques. Two types of on-axis and offaxis lenses with different focal lengths and of different apertures were designed to operate at wavelengths of 1·52 μm and 633 nm. The blazed profile of the onaxis and off-axis lenses was approximated by up to 16 and up to four discrete levels respectively. Dynamic, that is electrically switchable, lenses have been realized by filling the structured surface with liquid crystal. The optical properties of the lenses, such as the focal spot sizes and the diffraction efficiencies, were investigated. Further the switching behaviour of the dynamic lenses was studied. The design and fabrication of the static and dynamic, on-and off-axis Fresnel zone lenses as well as their optical and switching properties will be presented.
60 citations
TL;DR: Fresnel waveguide lenses having a graded-index (GRIN) distribution for the segmented quadratic phase modulation are demonstrated, and the GRIN Fresnel lenses exhibit excellent focusing characteristics and a very high efficiency, both limited only by diffraction.
Abstract: Fresnel waveguide lenses having a graded-index (GRIN) distribution for the segmented quadratic phase modulation are demonstrated. The GRIN Fresnel lenses exhibit excellent focusing characteristics and a very high efficiency, both limited only by diffraction. Graded-index Fresnel lenses (F/5, 1-mm aperture) were fabricated for the first time in amorphous As2S3 film waveguides on a thermally oxidized silicon substrate by the electron-beam direct writing technique. The nearly diffraction-limited focusing characteristics and a high efficiency (48%) were experimentally obtained. The theoretical analysis and fabrication process are presented, and experimental results are discussed on the focusing characteristics of the fabricated GRIN Fresnel waveguide lens.
57 citations
TL;DR: In this paper, the authors show that the transmission of a periodic grating with circular symmetry can be composed of the sum of the transmissions of positive and negative axicons of different orders.
Abstract: We show that the transmission of a periodic grating with circular symmetry can be composed of the sum of the transmissions of positive and negative axicons of different orders. The properties of the light beams generated by the gratings can be understood from the well-known properties of the light beam of an axicon, which is approximately a Bessel beam of zeroth order. The method is applied to a circular binary phase grating, which is investigated both theoretically and experimentally in the spatial domain and the Fourier domain. A simple and accurate method for determining the focal length of a lens with use of Bessel light beams is presented.
54 citations
TL;DR: In this paper, the authors explore the possibility of producing several beam shapes with conical or cylindrical geometry using conical lenses, and discuss optical schemes for generation of hollow laser beams; with 3D intensity distribution surrounding all directions, a dark core region can be obtained.
52 citations
"Quasi-achromatic Fresnel zone lens ..." refers background in this paper
...Therefore, axicons are normally used together with a lens [5,7]....
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...While a FZL is designed to have a point focus, axicons, on the other hand, are used for the generation of a Bessel intensity profile in the near field and a ring pattern in the far field [5–7]....
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