Reflectivity hemispherical total

A clear, roughly cubic crystal of edge 0.10-0.15 mm was chosen for data collection. A Picker automatic four-circle diffractometer, equipped with a fine-focus Mo anode tube, was used. High-angle reflections were accurately centered at a takeoff angle of and were used for a least-squares refinement of the ceil parameters. Data were collected and treated as described in a recent article. A complete hemisphere of data was collected for 26 < 55°. Intensities of three standards were collected at intervals of every 200 reflections. A total of 2418 independent intensity data were recorded. 

If the bodies participating in radiative exchange cannot be assumed to be black bodies, then the reflected radiation flows also have to be considered. In hollow enclosures, multiple reflection combined with partial absorption of the incident radiation takes place. A general solution for radiative exchange problems without simplifying assumptions is only possible in exceptional cases. If the boundary walls of the hollow enclosure are divided into isothermal zones, like in 5.5.2, then a relatively simple solution is obtained, if these zones behave like grey Lambert radiators. Each zone is characterised purely by its hemispherical total emissivity si — whilst at = is valid for its absorptivity, and for the reflectivity... 

An opaque body, with the hemispherical total reflectivity r = 0.15, reflects diffusely. Determine the intensity LIef of the reflected radiation and the absorbed radiative power... 

It can be seen from Equations 1.2 and 1.3 that the spatial resolution of infrared microspectroscopy can be improved by immersing the sample in a medium of high refractive index. This exactly what is done in attenuated total reflection (ATR) spectroscopy using a single-reflection hemispherical internal reflection element (IRE). Eor example, if a germanium n = 4.0) hemispherical IRE is used, not only... 

Dielectrics (insulating materials, with n = n2ln, and kx = k2 = 0) —Normal-hemispherical total or spectral reflectivity... 

Attenuated total internal reflection (ATR) probes offer several advantages over other probe types. ATR is a phenomenon that relies on a difference in the index of refraction of a crystal and that of the solution with which it is in contact to prevent light from escaping the crystal. Only the evanescent wave of the light interacts with the solution layer at the crystal face. The result is an optical pathlength of only a few microns. Typical designs make use of faceted crystals or hemispheres (see Figure 6.1). The most common ATR material in the UV-vis is sapphire. In rare cases, fused silica may be used. ATR allows spectra to be taken of neat samples with optical density (OD) of 500-1000... 

From Eqs. (31) and (32) it can be calculated that 75% of the total resistance between a hemispherical microelectrode and a counter-electrode comes from a hemisphere with a radius of only 2dme and a semi-ellipsoid of a similar size can be defined for a circular microelectrode [49]. For that reason, the measured resistance reflects the electrical properties of a very small sample region. Microelectrodes can therefore serve as local conductivity probes on inhomogeneous solids as long as conductivity gradients occur on a much larger length scale than dme (Va/a dm J)> the conductivity in the 75% hemisphere is almost constant and the local conductivity obtained with circular microelectrodes reads... 

Fig. 5.11 Schematic diagrams illustrating (A) an attenuated total reflection experiment at the interface between a hemispherical window and a test solution and (B) the evanescent wave, which decays rapidly with distance into the test medium.

In low-power LEDs, the encapsulant has the shape of a hemisphere, so that the angle of incidence at the encapsulant/air interface is always normal. As a result, total internal reflection does not occur at the encapsulant/air interface. 

Radiation from the sun can reach a surface three ways thus the total irradiance (denoted G for global) of a surface may consist of three components Gb, which is the direct beam irradiance arriving along an unobstructed straight path from sun to surface Ga, which is the diffuse irradiance (i.e., radiation scattered by the atmosphere) apparently arriving from all directions within the sky hemisphere and Gr, which is reflected irradiance from the ground surface or from other objects in the environment. Thus,G = Gb-l-Gd-l-Gr. 

When taking the total intensity of a light source where the intensity over a wavelength interval dX is given by l(X)dX, the total directional hemispherical reflectivity is given by... 

Figure 7 shows two designs of coverslip-form solid-immersion micropshere superlens we have proposed, a flat-top design (Fig. 7a), and a hemisphere-top design (Fig. 7b), both having a thickness similar to standard coverslip which is small enough for the superlens to be directly inserted into the gap between conventional microscope s objective lens and sample. The hemisphere-top curved surface in the design Fig. 7(b) is used to reduce the effect of total internal reflection from a flat surface. 

A final geometry exists for directional illumination, diffuse collection integrating sphere measurements. The 30/T geometry (30° incidence, total hemispherical collection) is specified by the American Society for Testing and Materials (ASTM) for the measurement of acoustical ceiling tile reflectance, The author knows of no other applications that specify this integrating sphere geometry. 

Spectralon exhibits almost perfectly Lambertian reflectance over most of its usable range of 200-2500 nm. The total hemispherical reflectance is generally greater than 95% from 250 to 2500 nm and in the vicinity of 99% from 350 to 1500 nm. The material also shows no strong absorbance bands anywhere in its range of use. Spectralon is also stable to > 300°C and may be heated and cooled with no changes in reflectance properties. 

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