Compensator plate

Asbestos, quartz or other minerals can be analyzed by consideration of mineralogical principles and crystal systems. Polarized light, compensation plates, measurement of angles of extinction and dispersion staining are useful techniques. Optical behavior of a mineral is related to the internal crystal structure of the mineral. Tables of optical constants are useful for mineral identification. The microscope is a powerful tool for analysis that should not be overlooked by the industrial hygiene chemist. 

On the cylindrical part of the core barrel in the zone of flow separator the compensating plates are placed with the help of which the design value of mounting clearance is achieved. In heating-up the reactor vessel and internals this clearance is decreased and the core barrel is clamped to the flow separator over the whole perimeter that reduces the vibration loads on the core barrel. Design of the core baffle channels is changed to smooth temperature fields in the baffle and to decrease the resulted deformations of the baffle. 

After being reflected at the plane mirrors Mi and M2, the two waves are superimposed in the plane of observation B. In order to compensate for the dispersion that beam 1 suffers by passing twice through the glass plate of beam splitter S, often an appropriate compensation plate P is placed in one side arm of the interferometer. The amplitudes of the two waves in the plane B are VtEAq, because each wave has been transmitted and reflected once at the beam splitter surface S. The phase difference 0 between the two waves is... 

Electronic cameras can operate in streak or framing mode. When the framing mode operates, after the completion of every frmning sequence, the electron beam is deflected by shift plates horizontally on the screen idiere a new image is formed. By compensating plates, the beam is deflected vertically, thus yielding two vertical pictures at every framing sequence. 

Fig. 1. Schematic of a Michelson interferometer. S in the FTPAS is a 100 watt tungsten iodide lamp. M is a movable front surface mirror, L is a collimating lens, M2 is a "stationary" front surface mirror that flutters to provide the analog of beam chopping in ordinary PAS, B is a half silvered beam splitter, C is a compensating plate, and D is the detector (a piezoelectric transducer, microphone, photomultiplier tube, or the eye of an observer).

Fig. 2. Schematic of light paths in a Michelson interferometer. Compensating plate has been omitted for clarity. See text for complete description.

The v sible wavelength beam splitter and compensating plate are both Yo (parallel to one second of arc) with 5 cm full aperture (Pyramid Optical Corp.). The beam splitter is located in a 45 optical mount (Burleigh) which is supported by a Star-Gimbal mount for adjustment. The fixed mirror is also the phase modulating mirror. In order to accomplish the phase modulation the mirror is mounted in a PZAT-90 (Burleigh) piezoelectric mount. There is sufficient linear motion available ( 10 micrometers/ 1000 V) from this mount to drive several orders of visible fringes. 

The disadvantages of double bottom designs (including, settlement, product entrapment and modification to nozzle compensating plates) are detailed in EEMUA 183. 

Figure 5.34. Variation of RT (= n) with wavenumber, v or a, normalized to the center wavenumber, vo or ao, for a sihcon film n = 3.6) on a calcium fluoride substrate (w2 = 1.4) with a Cap2 compensator plate of the same thickness, with 0 = 45°, calculated for the first hoop of the beamsplitter efficiency curve. (Originally reproduced from [46], by permission of the author.)...

A. Turner and H. M. Mould, Interferometer having combined beam splitter compensator plate, U.S. patent 5,808,739 (assigned to Perkin-Elmer Ltd., BeaconsUeld, Buckinghamsbire, England, September 15, 1998). 

A good description of all the factors contributing to the efficiency of an FT-IR spectrometer has been reported by Mattson [10]. He measured the effect of several different parameters that include beamsplitter efficiency, Fresnel losses at the substrate and compensator plate, reflection losses at the mirrors, radiation obscured by the mounting hardware for the HeNe laser, the emissivity of the source, and losses caused by imperfect optical alignment. He calculated the overall efficiency ( in Eq. 7.8) as being 0.096. This value is in accord with the value of 0.10 used in Section 7.1 to estimate the SNR of a commercial FT-IR spectrometer. 

The beamsplitter of the coating type is a combination of a substrate plate (e.g., a KBr plate) with a thin coating of a material (e.g., Ge) usually vapor-deposited onto one side of the plate and a compensation plate of the same shape. The wavenumber region covered by such a beamsplitter depends on the spectral characteristics of the substrate plate, the coating material, and the thickness of the coating. 

Imperfections or nonidealities of the optical components in an ellipsometer can cause errors in A and il/. Quantitative analyses of errors have been made by Jerrard for inexactness of the quarter-wave plate, by Azzam and Bashara" for nonideal optical activity of the quarter-wave plate and surface roughness, and by Smith" for finite bandwidths of the monochromatic light source as well as the source polarization. Archer and Shank" and Yolken, Waxier, and Kruger considered the effect of multiple reflection within the compensator plate. It is reported that antireflection coatings on the surfaces of the compensator plate are beneficial. Aspnes" treated in a formal way the first-order effects from... 

Figure 2 Optical arrangement of the Michelson interferometer. Mi is a fixed and M2 a moving mirror. BS is a beamsplitter and C a compensating plate. M is the image of M2 formed by BS.

In the near-IR region a beam-splitting film should be very thin. In this case it is necessary to use a low-absorption dielectric coating, which is deposited on a suitable substrate plate. A thin Ge layer deposited on a KBr substrate, with a KBr compensating plate, is a good beamsplitter in the wavenumber region 1000-4000 cm"b... 

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