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Light
Published in John Watkinson, Convergence in Broadcast and Communications Media, 2001
When such a wavefront arrives at an interface with a denser medium, such as the surface of a lens, the velocity of propagation is reduced; therefore the wavelength in the medium becomes shorter, causing the wavefront to leave the interface at a different angle (Figure 6.7). This is known as refraction. The ratio of velocity in vacuo to velocity in the medium is known as the refractive index of that medium; it determines the relationship between the angles of the incident and refracted wavefronts. Reflected light, however, leaves at the same angle to the normal as the incident light. If the speed of light in the medium varies with wavelength, dispersion takes place, where incident white light will be split into a rainbow-like spectrum leaving the interface at different angles. Glass used for chandeliers and cut glass is chosen to be highly dispersive, whereas glass for lenses in cameras and projectors will be chosen to have a refractive index which is as constant as possible with changing wavelength. The use of monochromatic light allows low-cost optics to be used as they only need to be corrected for a single wavelength. This is done in optical disk pickups and in colour projectors which use one optical system for each colour.
Optical and Video Principles
Published in John Watkinson, The Art of Digital Video, 2013
The wave theory of light suggests that a wavefront advances because an infinite number of point sources can be considered to emit spherical waves, which will add only when they are all in the same phase. This can occur only in the plane of the wavefront. Figure 2.6 shows that at all other angles, interference between spherical waves is destructive. Note the similarity with sound propagation described in Chapter 5. When such a wavefront arrives at an interface with a denser medium, such as the surface of a lens, the velocity of propagation is reduced; therefore the wavelength in the medium becomes shorter, causing the wavefront to leave the interface at a different angle (Figure 2.7). This is known as refraction. The ratio of velocity in vacuo to velocity in the medium is known as the refractive index of that medium; it determines the relationship between the angles of the incident and the refracted wavefronts. Reflected light, however, leaves at the same angle to the normal as the incident light. If the speed of light in the medium varies with wavelength, dispersion takes place, in which incident white light will be split into a rainbow-like spectrum, leaving the interface at different angles. Glass used for chandeliers and cut glass is chosen to be highly dispersive, whereas glass for lenses in cameras and projectors will be chosen to have a refractive index that is as constant as possible with changing wavelength. The use of monochromatic light allows low-cost optics to be used as they need to be corrected for only a single wavelength. This is done in optical disk pickups and in colour projectors that use one optical system for each colour.
Physical Modelling of Blast Effects in Rock Breakage
Published in V.A. Borovikov, I.F. Vanyagin, Modelling the Effects of Blasting on Rock Breakage, 2020
It is known that for each monochromatic light, there exists a specific wavelength λ=vT=v/pK;λ=c*/pK, where v and c* are velocity of light propagation through material and vacuum; T and pK the time period and frequency of vibration of wave. Thus, after obtaining different colours on the screen and knowing in advance the relationship between colour and wavelength, the relative difference G = nλ (where n is the sequence fringe number) and τmax from (3.23) are readily determined, i.e., τmax=nλ/(2Cσδ)=τ01.0n/δ, where τ01.0 is the optical constant of the material (rating of the band), which is the magnitude of stress required for varying the sequence of band n by one unit and is determined in advance on the specimen of model material by the method of comparison of colours of bands and method of compensation.
Advancing Radiative Heat Transfer Modeling in High-Temperature Liquid Salts
Published in Nuclear Science and Engineering, 2020
Carolyn Coyle, Emilio Baglietto, Charles Forsberg
The salt containment apparatus is then coupled to a BRUKER Vertex 70 FTIR spectrometer. As illustrated in Fig. 2a, light leaves the FTIR and is directed through the salt sample by a series of mirrors and finally to the detector. Unlike dispersive spectroscopy that uses monochromatic light, FTIR spectroscopy uses a broad-spectrum light source to obtain absorption data. The advantage of using this method is that high-spectral-resolution data for large wavelength regions can be obtained simultaneously. Additionally, the Vertex 70 uses a Michelson interferometer to modulate the signal from the IR source. This modulated light produces an alternating current signal that the detector electronics differentiate from the direct current signal originating from constant background emissions, as the salt itself will emit heavily at high temperatures.
Entanglement-enabled interferometry using telescopic arrays
Published in Journal of Modern Optics, 2020
Siddhartha Santra, Brian T. Kirby, Vladimir S. Malinovsky, Michael Brodsky
Interferometric measurements allow us to extract the phase information of radiation collected from spatially separated points (1, 19). This phase information can be used to distinguish the angular positions of different points at the source from which the radiation emerges, resulting in the resolution of different source points. The essential idea of interferometry can be understood through Young's double slit experiment (Figure 1). Plane waves of monochromatic light from a distant point source interfere on a second screen upon passing through two slits (the distance between screens is negligible compared to the distance to the source) resulting in an intensity pattern of alternating bright and dark fringes. In the case of two point sources, the interference patterns overlap. Two point sources are resolved if the central maximum of the interference pattern from one source coincides with the first minimum of the interference pattern from the other. When this happens, the angular separation of the two point sources (resolution) is defined as where λ is the wavelength of the monochromatic light, and B the separation between the slits.
Designing of TiO2/MWCNT Nanocomposites for Photocatalytic Degradation of Organic Dye
Published in Particulate Science and Technology, 2015
Silvana Da Dalt, Annelise K. Alves, Felipe A. Berutti, Carlos P. Bergmann
The crystallinity of the composites obtained was evaluated by the x-ray diffraction (XRD) technique using a Philips diffractometer (Model X'Pert MPD) equipped with a graphite monochromator and a copper anode, operating at 40 kV and 40 mA. Analyses were performed in a 2θ range of 20°–70°, with steps of 0.05° for 2 s, with Cu Kα radiation. The equipment JEM 1200EXII-120 kV was used to perform transmission electronic microscopy (TEM). The graphitization grade of the MWCNTs was investigated by Raman spectroscopy. The Raman spectra were obtained at room temperature using a Renishaw InVia spectrometer equipped with a He–Ne laser (λ = 532 nm). Diffuse reflectance spectroscopy (DRS) measures were used in order to determine the optical energy gap. The equipment used was a Cary 5000 UV–Vis–NIR spectrophotometer. The photoluminescence (PL) measures were obtained from the monochromatic light of a UV laser with 266 nm of wavelength. The signal emitted by the sample was dispersed by a monochromator (Princeton Instruments SP-2300i) and detected by a CCD camera. Measures of photocatalytic activity were carried in a system of twelve 8 W UV lamps emitting 365 nm of wavelength. The dye concentration was set to 1.0 × 10−5 mol/L. Spectrophotometry (Bioespectro SP 200) was used to determine the dye concentration of each collected sample. The photocatalityc activity efficiency related to the UV exposition time was measured from transmittance and calculated by comparing the dye concentration (C) in the system with the initial dye concentration (C0).