China
Africa
Explore chapters and articles related to this topic
Free-space Optics
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
In the following sections, we describe how to calculate the position and dimensions of laser beam waists when transformed by lenses. In geometrical optics, an object (loosely something that can be imaged) is considered to be the point of origin of a spherical wavefront, the radius of which equals the distance from the object. Given a lens (or, more generally, an optical imaging system) of focal length f, object (s) and image (s΄) distances from the (thin) lens is given by the well-known ‘lens formula’ [9]:1/s+1/s'=1/f
Prisms and Refractive Optical Components
Published in Daniel Malacara-Hernández, Brian J. Thompson, Fundamentals and Basic Optical Instruments, 2017
Daniel Malacara-Hernández, Duncan T. Moore
A lens has two spherical concave or convex surfaces. The optical axis is defined as the line that passes through the two centers of curvature. If the lens thickness is small compared with the diameter, it is considered a thin lens. The focal length f is the distance from the lens to the image when the object is a point located at an infinite distance from the lens, as shown in Figure 6.24. The object and the image have positions that are said to be conjugate to each other and related by 1f=1l′−1l , where l is the distance from the lens to the object and l′ is the distance from the lens to the image, as illustrated in Figure 6.25. Some definitions and properties of the object and image are given in Table 6.1.
L
Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[general] The lens maker equation uses the refraction concept to describe the formation of an image in a focal point (f) of a system of aspherical surfaces with respective radii Ri using Snell’s law as follows: 1/f=(n2−n1)/n1[(1/R1)−(1/R2)]=P, where n1 is the index of refraction of the surrounding medium, n2 the index of the refractive medium, and P the power of the lens expressed in diopters. For a thin lens, the lens maker equation reverts to (1/f)=(1/i)+(1/o), where i is the image distance to the lens and o is the object distance (see Figure L.85).
Sub-diffraction focusing of light by aperiodic masks
Published in Journal of Modern Optics, 2022
Seyeddyako Mostafavi, Ferhat Nutku, Yasa Ekşioğlu
In the first type simulations focusing properties of aperiodic hollow masks were investigated. Point-like light source with spherical wavefronts placed at right of the mask where the focal point searched at . Diffraction patterns of various masks are given in Figure 3. Thue-Morse and its conjugate structure present a focal point where diffraction mask operates like a convergent thin lens. Brightness of the focal point obtained by Thue-Morse mask is higher than the one obtained by its conjugate as seen in Figure 3(b,e). These two intensity profiles stem from the symmetric distribution of the holes in the Thue-Morse type masks. Its observed that Fibonacci and Rudin-Shapiro type masks cannot focus light as a convergent thin lens.
Liquid crystal technology for vergence-accommodation conflicts in augmented reality and virtual reality systems: a review
Published in Liquid Crystals Reviews, 2021
LC features an electrically tunable refractive index, which depends on its molecular orientation with respect to the polarization state of light. Therefore, by controlling the LC molecular orientations, different types of LC lenses have been developed and adopted in AR systems [20–22]. Figure 7 illustrates an optical medium that converts a plane wave into a convergent or divergent wave, and such an optical medium is a lens. More precisely, we assume that the electric field of the incident light is U(r) and the output electric field is U’(r), where r is the radial position in the xy-plane (). We assume that the polarization of the input and output light are identical. The transfer function (t(r)) of the optical medium is defined as [38]: where A is the coefficient of amplitude modulation, and is the optical phase. Without scattering and absorption, A can be neglected (A =1). When the wavefront of the output light is a paraboloidal wave under paraxial approximation (or thin-lens approximation), can be further expressed as
Liquid crystal Pancharatnam-Berry phase lens with spatially separated focuses
Published in Liquid Crystals, 2019
Yaqin Zhou, Yue Yin, Yide Yuan, Tiegang Lin, Huihui Huang, Lishuang Yao, Xiaoqian Wang, Alwin M. W. Tam, Fan Fan, Shuangchun Wen
With the development of micro/nano-fabrication technologies and new materials, new ultra-thin flat lenses are emerging, which are normally formed by micro/nano-structures, with thickness in the level nanometres or micrometres [8,9]. Compared with conventional refractive lenses, the new ultra-thin lenses show good potential to form highly integrated and compact size optical systems. There are several kinds of ultra-thin flat lenses, including the metalenses which are composed of periodic subwavelength dielectric or metal structures [10,11], and the liquid crystal (LC) lens based on Pancharatnam-Berry (PB) phase modulation [12–14]. The metalenses are normally fabricated by techniques including electro-beam lithography and photolithography technologies [15,16], most of which are too complex, time-comsuming and equipment-required, leading the metalens size limited to submillimetre size. Different from metalenses, the fabrication of LC ultra-thin lenses is based on the LC photoalignment technology [17], providing us an easier, cheaper and more convenient way to fabricate an ultra-thin lens via manipulating the optical axis orientation of the LC molecules [18,19].