scholarly journals Compact diffractive optics for THz imaging

2018 ◽  
Vol 58 (1) ◽  
Author(s):  
Linas Minkevičius ◽  
Simonas Indrišiūnas ◽  
Ramūnas Šniaukas ◽  
Gediminas Račiukaitis ◽  
Vytautas Janonis ◽  
...  
Keyword(s):  
Spherical Surface ◽  
Focal Depth ◽  
Numerical Aperture ◽  
Picosecond Laser ◽  
Fresnel Lens ◽  
Diffractive Optics ◽  
Direct Writing ◽  
Thz Imaging ◽  
Beam Focusing ◽  
Phase Quantization

We present a compact diffractive silicon-based multilevel phase Fresnel lens (MPFL) with up to 50 mm in diameter and a numerical aperture up to 0.86 designed and fabricated for compact terahertz (THz) imaging systems. The laser direct writing technology based on a picosecond laser was used to fabricate diffractive optics on silicon with a different number of phase quantization levels P reaching an almost kinoform spherical surface needed for efficient THz beam focusing. Focusing performance was investigated by measuring Gaussian beam intensity distribution in the focal plane and along the optical axis of the lens. The beam waist and the focal depth for each MPFL were evaluated. The influence of the phase quantization number on the focused beam amplitude was estimated, and the power transmission efficiency reaching more than 90% was revealed. The THz imaging of less than 1 mm using a robust 50 mm diameter multilevel THz lens was achieved and demonstrated at 580 GHz frequency.

A Novel High Concentration Fresnel Lens as a Solar Concentrator

2021 ◽  
pp. 1-29
Author(s):  
Kuldeep Awasthi ◽  
Desireddy Shashidhar Reddy ◽  
Mohd. Kaleem Khan
Keyword(s):  
Optical Axis ◽  
Spherical Aberration ◽  
Spherical Surface ◽  
Fresnel Lens ◽  
High Concentration ◽  
Aperture Diameter ◽  
Convex Lens ◽  
Flat Base ◽  
Fresnel Lenses ◽  
Outer Vertex

Abstract This paper describes the design methodology for a novel Fresnel lens. The original Fresnel lens is obtained from a plano-convex lens, whose spherical surface is split into a number of divisions (called facets), collapsed onto the flat base. Thus, all the facets of the original Fresnel lens have the same radius as that of the plano-convex lens. The proposed design aims to achieve better ray concentration and reduced spherical aberration than the original Fresnel lens by constructing spherical facets with unequal radii. The centers and radii of facets are constrained so that the ray refracted from the bottom vertex of each facet on one side of the optical axis and the ray refracted from the outer vertex of the corresponding facet on the other side of the optical axis must intersect at the focal plane. The proposed lens design has resulted in a 275% gain in the concentration ratio and a 72.5% reduction in the spherical aberration compared to the original lens of the same aperture diameter and number of facets. The performance of both novel and original Fresnel lenses when used as solar concentrators with a conical coil receiver is evaluated. The novel Fresnel lens led to increased heat gain and resulted in a compact solar collector design.

scholarly journals Rapid Fabrication of Continuous Surface Fresnel Microlens Array by Femtosecond Laser Focal Field Engineering

Micromachines ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 112 ◽  
Author(s):  
Linyu Yan ◽  
Dong Yang ◽  
Qihuang Gong ◽  
Yan Li
Keyword(s):  
Femtosecond Laser ◽  
Three Dimensional ◽  
Fresnel Lens ◽  
Two Dimensional ◽  
Direct Writing ◽  
Lens Array ◽  
Two Photon ◽  
Rapid Fabrication ◽  
Continuous Surface ◽  
Two Photon Polymerization

Femtosecond laser direct writing through two-photon polymerization has been widely used in precision fabrication of three-dimensional microstructures but is usually time consuming. In this article, we report the rapid fabrication of continuous surface Fresnel lens array through femtosecond laser three-dimensional focal field engineering. Each Fresnel lens is formed by continuous two-photon polymerization of the two-dimensional slices of the whole structure with one-dimensional scan of the corresponding two-dimensional engineered intensity distribution. Moreover, we anneal the lens array to improve its focusing and imaging performance.

Application of Fiber Point Diffraction in Measurement of Optical Surface

2011 ◽  
Vol 55-57 ◽  
pp. 1200-1205
Author(s):  
Liang Nie ◽  
Jun Han ◽  
Xu Jiang
Keyword(s):  
High Performance ◽  
Spherical Surface ◽  
Spherical Wave ◽  
Numerical Aperture ◽  
Single Mode ◽  
Single Mode Fiber ◽  
Optical Surface ◽  
Fiber System ◽  
Core Diameter ◽  
Fringe Contrast

The fiber point diffraction technology is applied in interferometer to measure optical surface with high precision. The wavefront diffracted from the single mode fiber with microns core diameter can be considered as ideal spherical wave and used as the referenced wave in interferometry. To estimate the quality of diffracted wavefront, the theoretical model of optical point diffraction is introduced at first. Based on the model, the influence of fiber core diameter, deformation and end-face shape on wavefront error is studied with numerical analysis. The analysis result shows that the single mode fiber used in experiment is available for instrument design and its influence over systematic error should be negligible within certain numerical aperture. Then a point diffraction interferometer with a single fiber is designed. Compared with the double fiber system, it has merit of noise immunity, high fringe contrast and high performance. Finally, the fiber point diffraction interferometer system is put up to measure spherical surface in experiment. The interference fringes are collected and analyzed with five-step shifting, least squares unwrapping and Zernike fitting method. The results show that the interferometer with optical fiber has achieved a worthy measurement precision and has great development potential.

scholarly journals Takagi-Taupin description of x-ray dynamical diffraction from diffractive optics with large numerical aperture

2007 ◽  
Vol 76 (11) ◽  
Author(s):  
Hanfei Yan ◽  
Jörg Maser ◽  
Albert Macrander ◽  
Qun Shen ◽  
Stefan Vogt ◽  
...  
Keyword(s):  
Numerical Aperture ◽  
Diffractive Optics ◽  
Dynamical Diffraction ◽  
X Ray

scholarly journals DEEP FOCUS; A DIGITAL IMAGE PROCESSING TECHNIQUE TO PRODUCE IMPROVED FOCAL DEPTH IN LIGHT MICROSCOPY

2011 ◽  
Vol 19 (3) ◽  
pp. 163 ◽  
Author(s):  
Noel T Goldsmith
Keyword(s):  
Light Microscopy ◽  
Digital Image ◽  
Computer Control ◽  
Focal Depth ◽  
Numerical Aperture ◽  
Depth Resolution ◽  
Processing Technique ◽  
Image Processing Technique ◽  
Composite Image ◽  
Deep Focus

In light microscopy, the spatial transverse resolution is a function of the wavelength and numerical aperture. The depth resolution is another function of these parameters. The factors that enable the detection of fine detail, make the sharp focusing of more than a thin slice of the depth in an object impossible. When the examination of fracture surfaces is attempted using light reflection microscopy, the roughness will often restrict the in-focus parts of an image to a small portion of the field of view. Several authors have presented methods that enable a set of digitised images to be processed into a single composite image which contains the in-focus parts from each image. These methods are effective, unfortunately the noise present in each digital image is accumulated, resulting in increasingly noisy composite images as the number of images in a set is increased. During processing, a separate image depicting the heights in the surface, i.e. a contour map, may be produced. This image is the key that enables the production of an in focus composite image which does not accumulate noise. Image analysis under computer control will frequently require the use of automatic focusing. Several authors have published criteria which may be used to determine the state of focus of an image. Such criteria have a clear application to the above process. This paper presents an evaluation of some methods used for the processing of such images, and also some procedures used for the determination of sharpness of focus and demonstrates a sensitive method for the evaluation of such procedures. Finally, an implementation of a method which uses the one of the simplest focus criteria is presented, and a procedure for the production of deep focus images which are free from the accumulation of noise.

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