Interference, optical

The measurement of surface forces calls for a rigid apparatus that exhibits a high force sensitivity as well as distance measurement and control on a subnanometre scale [38]. Most SFAs make use of an optical interference teclmique to measure distances and hence forces between surfaces. Alternative distance measurements have been developed in recent years—predominantly capacitive techniques, which allow for faster and simpler acquisition of an averaged distance [H, 39, 40] or even allow for simultaneous dielectric loss measurements at a confined interface. 

Crystallization. Acidified aluminum sulfate solutions can be supercooled 10 °C or more below the saturation point. However, once nucleation begins, the crystallization rate is rapid and the supersaturated solution sets up. The onset of nucleation in a gentiy stirred supersaturated solution is marked by the appearance of silky, curling streamers of microscopic nuclei resulting from orientation effects of hydraulic currents on the thin, platelike crystals. Without agitation, nucleation in an acidified solution, in glass tubes, can yield extended crystalline membranes of such thinness to exhibit colors resulting from optical interference. 

Doll, W. Optical Interference Measurements and Fracture Mechanics Analysis of Crack Tip Craze Zones. Vol. 52/53, pp. 105 — 168. 

There are different techniques to evaluate the quantitative stress level in prototype and production products. They can predict potential problems. Included is the use of electrical resistance strain gauges bonded on the surface of the product. This popular method identifies external and internal stresses. Their various configurations are made to identify stresses in different directions. This technique has been extensively used for over a half century on very small to very large products such as toys to airplanes. There is the optical strain measurement system that is based on the principles of optical interference. It uses Moire, laser, or holographic interferometry (2,3,20). 

Good agreement is reported to exist between the Dugdale plastic zone model and optical interference experiments, performed at the tip of a crack. Morgan and Ward [79], Fraser and Ward [80] and more recently and extensively Doll and... 

H. Angus Macleod, 2001, Thin-Film Optical Filters, Third Edition, ISBN 0 7503 0688 2, loP, Institute of Physics Publishing, Bristol and Philadelphia Alfred Thelen, 1988, Design of Optical Interference Coatings, ISBN 0-07-063786-5, McGraw-Hill Book Compagny... 

As a major branch of nanotribology. Thin Film Lubrication (TFL) has drawn great concerns. The lubricant him of TFL, which exists in ultra precision instruments or machines, usually ranges from a few to tens of nanometres thick under the condition of point or line contacts with heavy load, high temperature, low speed, and low viscosity lubricant. One of the problems of TFL study is to measure the him thickness quickly and accurately. The optical method for measuring the lubricant him thickness has been widely used for many years. Goher and Cameron [3] successfully used the technique of interferometry to measure elastohydrody-namic lubrication him in the range from 100 nm to 1 /rm in 1967. Now the optical interference method and Frustrated Total Reflection (FTR) technique can measure the him thickness of nm order. 

The Relative Optical Interference Intensity Method presented in Section 2.2 was hrst developed by Professor Luo (one of the authors of this book) and his colleagues in 1994 [4,5], for measuring the nanoscale lubricant him thickness. 

This method was developed by Johnston et al. in 1991 and well described in Ref. [10], according to which the method is introduced as follows. The principle of optical interference is shown schematically in Fig. 1. A coating of transparent solid, typically silica, of known thickness, is deposited on top of the semi-reflecting layer. This solid thus permanently augments the thickness of any oil film present and is known as a "spacer layer. The destructive interference now obeys the equation ... 

The silica him thickness was determined as a function of the disk radius by an optical interference method using the spectrometer. A steel ball was loaded against the silica surface to obtain an interference pattern of a central, circular Hertzian area with surrounding circular fringes due to the air gap between the deformed ball and flat. The thickness of... 

Fig. 8—Resolution of film thickness versus optical interference intensity [4,5], (a) different wavelengths, (b) different refractive indexes.

Before being glued to the glass sample, one face of each mica sheet has to be coated or spread with a thin layer of silver in 50 — 60 nm thick (reflectivity 96 % —98 %) for facilitating the optical interference. As shown in Fig. 16(a), when a beam of white light goes up vertically through the lower sample and reaches the silver film, the beam is partly re-... 

In the past decade, effects of an EEF on the properties of lubrication and wear have attracted significant attention. Many experimental results indicate that the friction coefficient changes with the intensity of the EEF on tribo-pairs. These phenomena are thought to be that the EEF can enhance the electrochemical reaction between lubricants and the surfaces of tribo-pairs, change the tropism of polar lubricant molecules, or help the formation of ordered lubricant molecular layers [51,73-77]. An instrument for measuring lubricant film thickness with a technique of the relative optical interference intensity (ROII) has been developed by Luo et al. [4,48,51,78] to capture such real-time interference fringes and to study the phenomenon when an EEF is applied, which is helpful to the understanding of the mechanism of thin film lubrication under the action of the EEF. 

Luo, J. B., Wen, S. Z., and Huang, P., "Thin Film Lubrication. Part I. Study on the Transition Between EHL and Thin Film Lubrication Using Relative Optical Interference Intensity Technique," Wear, Vol. 194,1996,pp. 107-115. 

Contact ratio, a, is defined as the real contact area divided by the nominal contact zone, where the real contact area is referred to as the sum of all areas where film thickness is below a certain criterion in molecular scale. The contact area was measured by the technique of Relative Optical Interference Intensity (ROII) with a resolution of 0.5 nm in the vertical direction and 1 /xm in the horizontal direction [69]. 

Polished surface is usually observed by optical interference techniques, e.g.. Chapman MP2000+, WYKO, and Zygo. As shown in Table 1, different parameters of a polished surface, e.g., the surface waviness, roughness, flatness, dub-off, roll-... 

In addition to the chemical effects of varying salinity, there are optical interferences in colorimetric analysis which are peculiar to estuarine samples. Saline waters and river waters have, in the absence of colorimetric reagents, an apparent absorbance arising from ... 

When the reflectivity of the two end faces is low (e.g., 4% from an air-glass interface), the multiplex reflections in the cavity have negligible contribution to the optical interference. Under this circumstance, the FP cavity is commonly referred to as the low-finesse cavity and the signal can be modeled using a two-beam interference model, given by5,6 ... 

The MZI-CCMI and the MI-CCMI can be modeled using the following two-beam optical interference equation 5 6... 

An experimental method based on the theories for rainbow phenomena has been applied to the measurement of droplet size and velocity and to the detection of non-sphericity.[7] In this method, a comparison between two droplet diameters is deduced from two different optical interference patterns observed in a rainbow that is created by a droplet scattering laser light. Once a rainbow pattern is... 

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