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All About Wave Equations
Published in Bahman Zohuri, Patrick J. McDaniel, Electrical Brain Stimulation for the Treatment of Neurological Disorders, 2019
Bahman Zohuri, Patrick J. McDaniel
An interferometer is really, a precise scientific instrument designed to measure things with extraordinary accuracy. The basic idea of interferometry involves taking a beam of light (or another type of electromagnetic radiation) and splitting it into two equal halves using what’s called a beamsplitter (also called a half-transparent mirror or half-mirror). This is simply a piece of glass whose surface is very thinly coated with silver. If you shine light at it, half the light passes straight through and half of it reflects back, so the beam-splitter is like a cross between an ordinary piece of glass and a mirror. One of the beams (known as the reference beam) shines onto a mirror and from there to a screen, camera, or other detectors. The other beam shines at or through something you want to measure, onto a second mirror, back through the beam splitter, and onto the same screen. This second beam travels an extra distance (or in some other slightly different way) to the first beam, so it gets slightly out of step (out of phase).
Optical Interference
Published in Rajpal S. Sirohi, Optical Methods of Measurement, 2018
Interferometry is a technique of measurement that employs the interference of light waves, and the devices using this technique are known as interferometers. These use an arrangement to generate two beams, one of which acts as a reference and the other is a test beam. The test beam gathers information about the process to be measured or monitored. These two beams are later combined to produce an interference pattern that arises from the acquired phase difference. Interferometers based on division of amplitude use beam-splitters for splitting the beam into two and later combining them for interference. Ingenuity lies in designing beam-splitters and beam-combiners. The interference pattern is either recorded on a photographic plate or sensed by a photodetector or array-detector device. Currently charge-coupled device (CCD) arrays are used along with phase-shifting to display the desired information such as surface profile, height variation, and refractive index variation. Observation of the fringe pattern is completely hidden in the process.
Optical Sensing
Published in Araz Yacoubian, Optics Essentials, 2018
Optical interferometers are used for a variety of sensing applications. Interferometric sensors include the Michelson (see Figure 10.1), Mach-Zehnder (see Figure 10.2), Fabry-Perot (see Figure 10.3), and Sagnac (see Figure 10.4) interferometer sensors. These sensing systems can detect displacement, such as change in optical path length between the two arms of a Michelson interferometer or change in spacing between the two mirrors in a Fabry-Perot interferometer, change in refractive index, or change in wavelength of the light source. A Sagnac interferometer can sense rotation. Interferometric measurements are very sensitive and can measure dimensional changes many orders of magnitude smaller than the optical wavelength. To learn more about interferometry, it is best to start with a basic optics text [3–5], and then migrate to other texts specific to a particular field to which interferometers are applied.
Deep convolutional neural network for three-dimensional objects classification using off-axis digital Fresnel holography
Published in Journal of Modern Optics, 2022
B. Lokesh Reddy, R N Uma Mahesh, Anith Nelleri
Digital holography is an interferometric imaging technique, a single-shot off-axis digital hologram recording technique that is well suitable for imaging 3D objects. Figure 2 shows the experimental set-up of an off-axis digital holographic system configured in transmission mode using Mach–Zehnder interferometer geometry. The light beam emitted from the laser source (He–Ne laser) of wavelength is filtered using a spatial filter and collimated with the collimation lens of focal length . The collimated beam enters the Mach–Zehnder interferometer by splitting the beam into two arms using a BS1. In the object arm, a 3D object is placed at a distance ‘’ from the recording plane to form the object wave, and another arm forms the reference wave. At the interferometer exit (BS2), the object and reference waves are interfered with at an angle to form an off-axis digital Fresnel hologram. The CMOS sensor with square pixel pitch is used to record the off-axis digital Fresnel hologram.
Multi view interferometric tomography measurements of convective phenomena in a differentially-heated nanofluid layer
Published in Experimental Heat Transfer, 2022
S. Srinivas Rao, Atul Srivastava
The multi-view projection data of the convective flow field in the cylindrical tomographic test cell for any given working fluid medium have been mapped using the Mach-Zehnder interferometer. The assembly of the optical components for development of the laser interferometry was schematically shown in Figure 3. A He-Ne laser of 632.8 nm wavelength of coherent light source is aligned in-line with the spatial filter (objective lens of 40×) to form a diverging source of light beam. The diverging light beam was collimated using an achromatic doublet lens, through placing the lens at its focal length from the spatial filter. The optical components consigned for assembling the present interferometer are consisting of 100 mm diameter size lens intended for achromatic doublet, mirrors, and beam splitters. The collimator consents to form an appropriate working collimated light beam of 60 mm in diameter. The collimated light beam is passed through first beam splitter (BS1) that splits light beam into two with 50% reflectivity and 50% transmissivity. The transmitted light beam is used as reference arm of the interferometer, whereas the reflected light beam from BS1 is used as the test arm of the interferometer by placing the test cavity in the direction of the light beam.
In-situ evaluation of C/SiC composites via an ultraviolet imaging system and microstructure based digital image correlation
Published in Nondestructive Testing and Evaluation, 2018
For the high temperature nondestructive imaging techniques used for in situ evaluation of materials, number of imaging techniques were developed. Optical fibre sensors [4], interferometric optical techniques including moiré interferometry (MI) [5], electronic speckle pattern interferometry (ESPI) [6], etc., and image-based non-interferometric optical techniques including the video-extensometer [7] and digital image correlation (DIC) [8] have been proposed and advocated for the high-temperature deformation measurements. However, the optical fibre sensors are easily broken, high in cost and with poor temperature stability [4]. Interferometric optical techniques are high sensitive to ambient vibrations and air disturbances along the optical paths, having complicated system configurations and cumbersome fringe processing. As a result, the optical fibre sensors and interferometric optical techniques are less popular for high-temperature deformation measurements. Just by comparison, as a typical non-contacting full field deformation measurement technique, DIC have advantages of simple experimental setup, preparation and procedure, low requirement on experimental environment, and wide range of resolution and applicability, has attracted increasingly attention and been convincingly demonstrated as a powerful technique for high-temperature deformation measurement.