A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Outdoor heat stress poses a serious public health threat and curtails industrial labor supply and productivity, thus adversely impacting the wellness and economy of the entire society. With climate change, there will be more intense and frequent heat waves that further present a grand challenge for sustainability. However, an efficient and economical method that can provide localized outdoor cooling of the human body without intensive energy input is lacking. Here, a novel spectrally selective nanocomposite textile for radiative outdoor cooling using zinc oxide nanoparticle-embedded polyethylene is demonstrated. By reflecting more than 90% solar irradiance and selectively transmitting out human body thermal radiation, this textile can enable simulated skin to avoid overheating by 5-13 °C compared to normal textile like cotton under peak daylight condition. Owing to its superior passive cooling capability and compatibility with large-scale production, this radiative outdoor cooling textile is promising to widely benefit the sustainability of society in many aspects spanning from health to economy.

Spectrally Selective Nanocomposite Textile for Outdoor Personal Cooling

Two- and multiple-beam interference fringes are used to measure the refractive index of graded index fibres. A general expression considering the refraction of the beam by the graded index fibre has been derived, from which expressions for homogeneous and skin-core fibres can be obtained. Comparison between the results with the method used when neglecting refraction is dealt with using Philips, LDF (TM) optical fibres and drawn polypropylene. Considering the derived expressions in the refractive index determination gives a correction even when a matching liquid is used, this suggests that the refraction method should be used especially for graded index fibre.

http://iopscience.iop.org/article/10.1088/0963-9659/4/3/004/pdf

On the determination of the refractive index of a fibre. II. Graded index fibre

A modified holographic interferometer is described which enables automatic fringe pattern analysis to be achieved when recording transient events. The introduction of a phase grating enables the method of phase-stepping fringe analysis to be applied to a wide range of measurement problems. The theory is developed, and an analysis of the sources of error is presented with the aid of computer simulations. Initial experimental results confirm the utility of the method and its potential application in pulsed laser holography. The method can in principle be applied to electronic speckle pattern interferometry.

Multichannel phase-stepped holographic interferometry

For the first time to our knowledge, digital holography is used to determine the distribution of parabolic or nonparabolic refractive index fields in graded index optical fibers. The fiber is embedded in an index matching fluid whose refractive index can be varied to a matching and mismatching index with respect to that of the cladding. In experiments for both cases high precision phase-shifting digital holographic interferometry is applied with numerical evaluation employing the multilayer model for recognition of the refraction. Due to the higher redundancy in the multiple phase-shifted holograms better accuracy can be obtained compared to classical two-beam interferometry. Therefore the holographic method is recommended as a nondestructive and noncontacting method for characterizing graded index optical fibers.

Characterization of graded index optical fibers by digital holographic interferometry

A multiple-beam interference Fizeau fringes technique is used to measure the refractive index profile of drawn polyethylene fiber. The interference fringe shift in the fiber region has been analyzed automatically using an interactive algorithm. The method takes into consideration the refraction of the light beam when crossing the fiber. Plane polarized light vibrating parallel and perpendicular to the fiber axis are used to obtain the refractive index profiles of both cases. These profiles are used to determine some optical parameters such as the birefringence, the optical orientation function, the polarizability per unit volume, and the value Δα/3αo, which related to the material structure. The reliability of the method is tested considering the results of drawn polyethylene fiber samples using the manual technique. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3099–3106, 2000

Refractive index profile of polyethylene fiber using interactive multiple‐beam fizeau fringe analysis

Automatic refractive index profiling of fibers by phase analysis method using Fourier transform

Two- and multiple-beam interferometric methods are used to study the refractive index profiles of cylindrical fibres having skin-core structure. The refraction of the incident beam inside the fibre is considered. Mathematical expressions are derived for this aim, and applied with two- and multiple-beam microinterferograms of cuperamonium, polypropylene, Roman nylon-6 (synthetic polymer fibres) and step index optical fibre. A comparison between the results and that in the case of non-distorted immersed wavefront is dealt with. The application of the derived expressions results shows a good correction of the results due to the mismatching effect. Microinterferograms are given for illustration.

https://iopscience.iop.org/article/10.1088/0963-9659/3/6/003/pdf

M.A. Mabrouk

Papers

On the determination of the refractive index of a fibre. II. Graded index fibre

Refractive index profile of polyethylene fiber using interactive multiple‐beam fizeau fringe analysis

Automatic refractive index profiling of fibers by phase analysis method using Fourier transform

On the determination of the refractive index of a fibre: I. Skin-core fibre

Determination of GR-IN optical fibre parameters from transverse interferograms considering the refraction of the incident ray by the fibre