Mirage effect

Gas-phase methanol hydrochlorination process, 16 322-323 Gas-phase mirage-effect spectroscopy,... 

Beam deflection — A deviation of the light beam wave-front when it passes from one medium to another with a different - refractive index, or through a medium with an inhomogeneous refractive index. The wavefront velocity is (v = c/n) and the wavelength (A) is related to n by A = vfy where c is the velocity of light in a vacuum, n is the refractive index of the medium and / is the beam frequency. Thus, the wavelength of a laser beam wave-front will increase when the refractive index of the electrolyte decreases [i]. See also - refraction or - mirage effect. 

Direct mirage effect — A deflection signal usually associated with photothermal experiments in which the deflected probe light beam passes on the same side of the photoilluminated -> interface [i]. See also - photothermal deflection spectroscopy. 

Mirage effect — The deflection of a probe light beam based on the refraction property. When a light beam... 

The term mirage effect has been indistinctly assigned to studies performed by - photothermal deflection spectroscopy (PDS) and - probe beam deflection (PBD). However, PDS is based on the analysis of the first term of the last equation, whilst in PBD, essentially the second term is evaluated. 

Photothermal deflection spectroscopy — Photothermal deflection is a photothermal spectroscopic technique used to detect the changes in the refractive index of the fluid above an illuminated sample by the deflection of a laser beam. There are two sources from which the thermal deflection effect might appear. One of them is produced by a gradient in the refractive index after a thermal excitation where the density also varies with temperature, in the so-called mirage effect. And the other one is produced by the topographical deformation of the surface over which the laser beam is reflected. This effect is known as photothermo-elastic effect or surface photothermal deflection [i]. 

Among the large variety of in situ experiments that have been described one can distinguish (1) those whose purpose is investigation of the electrochemical doping process itself cyclic voltammetry, quartz balance [17], mirage effect [18], and ellipsometry [19], and (2) those developed for studies of the properties of the CP UV-near-IR spectroscopy [20], IR [21], ESR [22], conductivity [23], impedence [24], and so on. 

An alternative technique is the so-called Photothermal Beam Deflection Spectroscopy [PBDS], based on the so-called mirage effect first reported by Boccarra and coworkers [39, 40]. In this case, the periodic temperature rise caused by the absorption of the modulated IR radiation (i.e. the photothermal effect) is detected optically because it causes periodic deflections of a laser beam passing close to the surface of the solid sample. The PBDS technique has some advantages over the PAS technique, because of its lower Hmits of sample dimensions, but it has disadvantages because of the critical geometric setup. Like PAS, PBDS can have advantages with respect to traditional IR technique for the detection of surface... 

Photo acoustic microscopy Fast 1 pm Only polls the surface Mirage effect Position of coating delaminations, and surface-connected cracks... 

The concentration gradient of species moving either toward the electrode or into the solution can be measured with the probe beam deflection (PBD also called the Mirage effect) technique [100-104]. A light beam (in practically all reported cases,... 

Another important apparatus is the surface stress meter that allows measurement of the surface stresses (since the stress component normal to the surface is null). Using the mirage effect due to the tin concentration gradient at the tin side... 

Variants of these techniques are the Photothermal Deflection Spectroscopy (PDS or Mirage effect) and Photothermal Displacement Spectroscopy (102). These techniques are based on deflection of a light beam due to refractive index gradients either In a fluid (or air) in contact with a light absorbing solid or in the solid itself. If the fluid is inert the technique can be used to measure absorption spectra of solid materials and transport properties. A version of these techniques was applied to electrochemical and photoelectrochemical systems (103). The authors describe the experimental conditions needed to separate the contributions from the temperature and concentration gradients. Once this is done the results can be correlated with the kinetics and mechanism of the electrochemical reactions. 

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