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Radiation—ionising and non-ionising
Published in Sue Reed, Dino Pisaniello, Geza Benke, Kerrie Burton, Principles of Occupational Health & Hygiene, 2020
LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Lasers currently produce light in the ultraviolet, visible or infrared region of the electromagnetic spectrum. Laser light differs from ordinary electromagnetic radiation in that the light beam is coherent in space (all the waves are in phase) and time (all the waves are of the same frequency). This means that the beam has very little divergence and is able to be transmitted large distances while retaining a relatively high level of energy per unit area. In other words, a laser beam remains very intense over long distances. This is in contrast to ordinary electromagnetic radiation, whose intensity falls off with the square of distance. Lasers produce a single or narrow-wavelength band.
Radiation—ionising and non-ionising
Published in Sue Reed, Dino Pisaniello, Geza Benke, Principles of Occupational Health & Hygiene, 2020
LASER is an acronym for light amplification by stimulated emission of radiation. Lasers currently produce light in the ultraviolet, visible or infrared region of the electromagnetic spectrum. Laser light differs from ordinary electromagnetic radiation in that the light beam is coherent in space (all the waves are in phase) and time (all the waves are of the same frequency). As a result, the beam has very little divergence and is able to be transmitted over large distances while retaining a relatively high level of energy per unit area. In other words, a laser beam remains very intense over long distances. This is in contrast to ordinary light, the intensity of which falls off with the square of distance. Lasers produce a single or narrow wavelength band of light.
Dosimetry
Published in Jitendra Behari, Radio Frequency and Microwave Effects on Biological Tissues, 2019
From Equation (3.8), it is apparent that the rate of change of temperature with time is the unknown that needs to be determined. Several optical temperature sensors take advantage of the fact that optical fibers, being low loss dielectrics, are neither directly heated by an electromagnetic field nor do they perturb it. In the liquid crystal, optical fiber probe with a strong temperature dependence of the reflectance of red light by the liquid crystal is used. The liquid crystal medium is sealed between a glass lance and a fiber optic catheter. Light (670 nm) emitted by the sensor is carried to a photo detector, which in turn converts light into electrical signal (voltage). An increase in the temperature of the sensor results in an increased reflectance from the crystal and subsequently an increase in the detected voltage. The shape and position of the liquid meniscus vary with temperature. The light beam is carried by optical fibers.
A review of NDE techniques for hydrogels
Published in Nondestructive Testing and Evaluation, 2023
Sasidhar Potukuchi, Viswanath Chinthapenta, Gangadharan Raju
Shearography, also called speckle pattern shearing interferometry, is a full-field detection method that can estimate the mechanical deformation of a sample. It has the capability to inspect relatively large areas at a given time. As shown in Figure 11, this technique uses highly coherent laser light to illuminate a sample that scatters and reflects the light beam. This creates an interference pattern called a speckle which passes through a shearing device (example, Michelson interferometer) and splits the beam into two images. The polariser nullifies one of these images, and the camera captures the other one as a fringe pattern. This process is repeated twice to detect defects or flaws, once without loading the sample and once on loading the sample. The difference in the two fringe patterns highlights the defect.
Optical design of a null test for off-axis three-mirror system based on refractive-diffractive zoom hybrid compensator
Published in Journal of Modern Optics, 2022
Lai Xiaoxiao, Chang Jun, Li Yiting, Ji Zhongye, Cao Jiajing, Li Dongmei
The principle of the null test is depicted in Figure 2. The collimator collimates the light source from a laser into a parallel beam, then the light beam incidents on the reference mirror of the interferometer. A part of the beam is reflected by the reference mirror and the splitter, finally images on the detector by an imaging lens. Other rays continue to transmit, and also image on the detector after being modulated by the compensator, and reflected by the tested aspheric mirror. The compensator is used to generate an aspherical wavefront to nullify the surface normal wavefront of the tested aspheric mirror. This test light will interfere with the reference light, so interferograms will be seen on the detector. If there is no surface error in the aspheric surface to be tested, a null fringe will be observed on the detector. Otherwise, a non-null fringe will be observed, which carries the surface information of the tested aspheric mirror, and the specific surface error of the tested aspheric mirror can be obtained by analyzing the non-null fringe.
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
Three-dimensional reconstruction of temperature fields and the convective flow phenomenon in the cylindrical heated cavity were determined using the path-averaged temperature fields obtained from multiple view angles. Laser interferometry results in the path-averaged data along the direction of propagation of the light beam. Hence, the principles of the optical tomography have been employed for obtaining the complete local distribution of the temperature field from the recorded projection data of the view angles. The multi-view projections (i.e., nearly 18 view angles from 0° to 360° revolution) have been employed for the reconstruction of select horizontal planes using the iterative MART algorithm. The tomographic reconstructions have been performed for the basefluid (EGD) and the varying dilute volume concentrations of Al2O3/EGD nanofluid (0.005% and 0.01%) to the cavity temperature differences of 1.0, 1.4, and 2.0°C. One of the primary interests of tomographic reconstructions is to deduce the possible fluid motion in the cavity and its dependence on the varying levels of volumetric concentrations of dilute nanofluids.