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Robotic Laser Measurement Technique for Solid Sound Field Intensity
Published in Chunguang Xu, Robotic Nondestructive Testing Technology, 2022
In the laser vibration measurement, the laser beam is focused on the measured structure, whose moment of force causes the Doppler Effect in laser reflection. If the object can reflect the beam correctly, its velocity and displacement can be calculated. Because of the high frequency of the laser, direct demodulation is not possible. Instead, the scattered beam is coherently mixed with the reference beam through an interferometer. The schematic diagram of laser interferometry is shown in Figure 14.22. The laser source emits a spatially and temporally coherent beam (in which all the photons have the same frequency, direction and phase), which is divided into a reference beam and an objective beam. The scattered beam and the reference beam are recombined and received by a photodetector that measures the intensity of the mixed light. The intensity varies with the phase difference ΔΦ between the two beams according to the following formula [35,36]: I(Δϕ)=Imax2(1+cosΔf)
Optical Interference
Published in Rajpal S. Sirohi, Optical Methods of Measurement, 2018
In order to study small objects, it is necessary to magnify them. The response of micromechanical components to an external agency can be studied under magnification. Therefore, microinterferometers, particularly Michelson interferometers, have been built that can be placed in front of a microscope objective. Obviously, one requires microscope objectives with long working distances. The Mirau interferometer employs a very compact optical system that can be incorporated in a microscope objective. It is more compact than the micro-Michelson interferometer and fully compensated. Figure 2.13 shows a schematic view of the Mirau interferometer. Light from the illuminator through the microscope objective illuminates the object. The beam from the illuminator is split into two parts by the beam-splitter. One part illuminates the object, while the other is directed toward a reference surface. On reflection from the reference surface as well as from the object, the beams combine at the beam-splitter, which directs these beams to the microscope objective. An interference pattern is thus observed between the reference beam and the object beam. The pattern represents the path variations on the surface of the object. White light can be used with a Mirau interferometer. Phase-shifting is introduced by mounting the beam-splitter on PZT (lead zirconate titanate).
Holography
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
There are two very different techniques for manufacturing holograms. One can either compute it, or record it optically. Computing the hologram involves the calculation of the position of the apertures and/or phase shifters, according to the laws of light propagation derived by Maxwell [8]. This calculation can be fairly easy for simple wavefronts, such as a lens, to extremely complicated for high-resolution three-dimensional images. To optically record a hologram, the amplitude and the phase of the wavefront need to be captured. Recording the intensity was first achieved with the invention of photography by Niépce in 1822, but recording the phase eluded scientists until 1948. Although the concept of optical interference was known for ages, it is Gabor [9, 10] who introduced the concept of making an object beam interfere with a reference beam to reveal and record the phase. Indeed, when two coherent beams intersect, constructive and destructive interferences occur according to the phase difference; this transforms the phase information into intensity information that can be recorded the same way photographs are taken. In some sense, the reference beam is used to generate a wave carrier that is modulated by the information provided by the object wave.
A review of NDE techniques for hydrogels
Published in Nondestructive Testing and Evaluation, 2023
Sasidhar Potukuchi, Viswanath Chinthapenta, Gangadharan Raju
Figure 8 shows the schematic and working principle of the conventional Time Domain OCT setup, which has a moveable reference mirror. As shown in the figure, this technique uses a light source that emits low coherence light, which divides into two beams: a reference beam that travels towards the reference mirror and a sample beam that moves towards the sample. The reference beam is reflected by the reference mirror along the same path as before. The sample beam is passed through a lens to obtain a beam of specific parameters like intensity, beam shape, etc., after which the beam is backscattered by the sample. The reflected light of the reference beam and the backscattered light of the sample beam recombine at the beam splitter to generate an interference pattern that is captured by the photodetector. The photodetector is connected to a computer that can regenerate the images using software tools.
Characterization of thermal sprayed Si on sintered SiC for space optical applications
Published in Surface Engineering, 2021
Tayaramma D. P. V. Jalluri, S. Somashekar, Arjun Dey, R. Venkateswaran, S. Elumalai, B. Rudraswamy, K. V. Sriram
The functional performance is evaluated using interferometric measurements of ‘surface figure’ and ‘surface finish’ (micro-roughness). Interferometric testing is a proven and comprehensive evaluation method to carry out surface figure evaluation of polished optical substrates [38]. In this method, the optical beam from the testpiece is interfered with a reference beam generated internally and the result being interference fringes that are depictive of the deviations of the surface from the ideal one. The interferometric testing is done with a interferometer (M/s. ADE phaseshift Technology, model: Minifiz). A high-quality Zygo transmission flat (transmission wavefront error of λ/10 PV @ 633 nm) is used to test the polished samples with the live interferogram being displayed in the monitor. Typical test set-up of interferometer is shown in Figure 5.
Photoelastic digital holographic polariscope
Published in Journal of Modern Optics, 2019
Binu P. Thomas, S. Annamala Pillai, C. S. Narayanamurthy
Experiments using both birefringent and non-birefringent specimens (same as that used for simulations as well as for conventional polariscope) as objects are conducted using Digital holographic polariscope. Figure 1 shows the proposed digital holographic polariscope arrangement with the monochromatic laser source (Laser quantum Torus, λ = 532 nm, CW power = 0.5 W, 120–240, frequency = 50–60 Hz) for recording isochromatic and isopachic fringes of stressed birefringent and non-birefringent specimens. The unexpanded laser is then split into two by a non-polarizing beam splitter. One of the beams coming from beam splitter passes through a circular polarizer as shown in Figure 1. This beam is expanded and collimated using spatial filter assembly and a collimator and then passes through the transparent birefringent specimen under test and then reaches CCD camera. This beam is called object beam and one can introduce a diffuser behind the object for removing isochromatic fringes but it is not shown in Figure 1. The other beam split from beam splitter passes through a circular polarizer and spatial filter assembly and interferes with the object beam at CCD camera plane. This beam acts as a reference beam for recording hologram. Now both the object beam and reference beams are circularly polarized and they interfere at CCD camera and this interference pattern is recorded by CCD and is numerically reconstructed with the help of HDigitalRT software (23) to reconstruct the hologram of object specimen.