Thickness Of Transparent Material Research Articles

Optical interference system for simultaneously measuring refractive index and thickness of slim transparent plate

Measuring the refractive index and thickness of transparent materials is essential in offline or online automated inspection in the manufacturing and industrial fields. We recently developed a novel optical system with two optical paths for simultaneously measuring the refractive index and thickness (>1 mm) of a transparent plate; the developed system allowed for better thickness measurement with a simpler structure and lower cost (C. S. Liu, R. C. Song, and S. J. Fu, Appl. Phys. B 125, 199, 2019). In the present study, the thickness range that can be measured using the developed optical system is reduced to ≤100 μm by using interference methods instead of triangulation methods. The proposed optical interference system is characterized numerically using simulations on the commercial software program ZEMAX and then experimentally tested using a laboratory-built prototype. The experiment results show that the refractive indexes and the thicknesses of the slim transparent plates (thickness ≤ 100 μm) were measured with high accuracy (with maximum measurement errors of 0.0007 and 3 μm for a refractive index n and thickness d, respectively). Consequently, the proposed optical interference system has the potential to be used in the automated inspection of slim transparent materials.

Efficiency-Improved UWB Transparent Antennas Using ITO/Ag/ITO Multilayer Electrode Films

In this paper, a transparent antenna made with a new structure of ITO/Ag/ITO is proposed. Overcoming the physical limitations of transparency and conductivity is an important problem with transparent materials. By studying and comparing previously reported transprent materials, a transparent electrode with thin film Ag inserted between two layers of ITO instead of a single layer is selected for a highly efficient transparent antenna. This electrode has low sheet resistance (3.1 Ω/sq) relative to its high transparency (88 % at 550 nm), which is a factor that can increase the efficiency of the antenna. In general, it is difficult to measure sheet resistance (SR) using a 4-point DC probe for very thin films (thickness of transparent material is less than the skin-depth). Therefore, a form of reverse engineering that can estimate DC sheet resistance using RF SR was presented and verified. As a result, it was possible to predict and design the performance of the transparent antenna with the new material structure. The selected transparent material is applied to design the wideband transparent antenna and the design process for wideband performance is covered in the paper. The proposed antenna with ITO/Ag/ITO was implemented for verification. The peak efficiency of the fabricated antenna was 66 %, and the measured bandwidth was 123 % (from 2.5 GHz to 10.6 GHz), which is the best performance than previously reported transparent antennas.

Terahertz Displacement and Thickness Sensor with Micrometer Resolution and Centimeter Dynamic Range.

Measuring distance and thickness simultaneously is important in biological, medical, electronic, and various industries. Herein, we propose a method for simultaneously measuring the displacement and thickness of transparent materials using a pulsed terahertz wave. For this technique, a beam splitter was used to design the optical path such that the terahertz wave would incident the specimen vertically to achieve centimeter measurement range and micrometer resolution. The measured terahertz waveform carries peak time information reflected from the upper and lower surfaces of the sample, and the thickness can be calculated using the time difference between the first and second reflected peaks. The displacement can also be calculated using peak time difference when the sample moves from the initial position to the changed position. For validation, an experimental test was performed using aluminum, acrylic, and glass plates. The results confirmed a measurement range of 1 cm with an error of less than 23 μm, and the thickness error was less than 8 μm.

Simultaneous measurement of refractive index and thickness of transparent material by dual-beam confocal microscopy

We propose and demonstrate a novel technique, termed dual-beam confocal microscopy, for the simultaneous measurement of the refractive index and geometrical thickness of a single layer. The technique is based on the creation of two closely spaced lateral confocal gates for the two orthogonal polarization states of a laser beam in a sample via a Nomarski prism. Thereafter, by applying Gaussian beam theory, the refractive index can be determined with an error of 1% or less for a commercial cover glass. Based on the measured refractive index, the thickness of the sample can also be calculated. To verify the proposed methodology and optical setup, a microlens array was scanned, with the surface profile and refractive index subsequently compared with their catalog specifications.

Diffuse reflectance of whole blood: model for a diverging light beam.

Previous theories describing the optical properties of whole blood have assumed a collimated light source in the derivation of reflectance and transmittance equations. However, many practical instruments which measure blood oxygen rely on noncollimated LED's and optical fibers as light sources. In addition, in the case of blood-perfused cuvettes, the light source is not in direct contact with the blood. Thus, many theories have limited applicability to practical instruments. Therefore, we present here an existing photon diffusion theory that we have generalized to account for the effects of a diverging light source and a thickness of transparent material between the light source and the blood. Comparisons to experimental data are made for both the new equation and the previous one. Better results are obtained with the new equation when applied to a cuvette geometry which is more accurately described by the generalized parameters. Limitations of both the new equation and the photon diffusion approximation in general are discussed.

Fabry-Perot laser interferometry to measure refractive index or thickness of transparent materials

By introducing a transparent plane parallel plate into an open Fabry-Perot cavity and counting the change in the interference order while the plate is rotated, it is possible to measure the thickness or refractive index of the material with a high degree of accuracy. The method of multipass interferometry can be applied by using a He-Ne laser of 632.8 nm wavelength.

Optical Measurements of Surface Films. I

Practical information is given concerning the calibration of an instrument called the ellipsometer, which is used to measure thicknesses from one angstrom unit up to many thousands angstrom units of transparent films deposited on polished metal slides. The instrument is a half-shadow instrument taking advantage of the ellipticity of polarized light reflected from film-coated metallic surfaces. The half-shadow is produced by depositing a different thickness of transparent material on the lower and upper part of the slides, or by evaporating directly on the lower part of chromium slides a thin layer of gold.