Quartz wedge

Quarz-keil, m. (Optica) quartz wedge, -kiesel, m. quartz gravel, -kristall, m. quartz crystal, rock crystal. -lager, n. quartz deposit, -linse, /. quartz lens, -mehl, -pulver, n. quartz powder- -rohr, n., -rohre, /. quartz tube, -sand, m. quartz sand, -scheibe, /. 

A detailed analysis of the experimentally obtained polarization patterns allows to determine all susceptibility components of the LB films.16,49 The values of the susceptibility were calibrated using a quartz wedge ([Pg.558]

Fig. 54. a. Two urea crystals of the same thickness, crossed at right angles. At the centre overlapping portion the combination appears isotropic, b. Effect of quartz wedge on crystal of NH4H2P04. As the wedge advances, the colour contours move towards the thicker part of the crystal. 

The distinction between the vibration directions of higher and lower refractive indices can always be made in this way for crystals having inclined extinction no less than for those with parallel extinction. When refractive indices are measured by the methods already given, the use of the quartz wedge is hardly necessary (unless for confirmation of conclusions already reached) but in other circumstances (for instance, when crystals are being examined in their mother liquor), quartz wedge observations are useful clues to optical character. 

Fig. 55. Effect of quartz wedge on convergent light figures, a. Uniaxial positive. b. Uniaxial negative, c. Biaxial positive, d. Biaxial negative.

If a uniaxial convergent light figure is seen, the optical sign of the crystal may Tbe checked by the use of the quartz wedge in the manner described in the previous chapter. This is not necessary (except as confirmation) unless for any reason it is not possible to obtain actual measurements of both a> and e. 

Figure 2-1 of Chapter 2 shows an experimental configuration for depolarization measurements in 90° scattering geometry. In this case, the polarizer is not used because the incident laser beam is almost completely polarized in the z direction. If a premonochromator is placed in front of the laser, a polarizer must be inserted to ensure complete polarization. The scrambler (crystal quartz wedge) must always be placed after the analyzer since the monochromator gratings show different efficiencies for L and polarized light. For information on precise measurements of depolarization ratios, see Refs. 21-24. 

Newton s series n. The sequence of interference colors observed when a quartz wedge is turned to the 45° position and observed between crossed polars. It is divided into orders by the red bands, which occur periodically as the thickness increases. It is identical with the interference colors from a thin isotropic film of gradually increasing thickness. 

The Babinet compensator is two quartz wedges of opposite sign mounted one above the other. One is fixed, the other movable with a micrometer. Range is 2000 nm. 

The quartz wedge is very useful for rapid qualitative observations of the sign of birefringence. Some wedges are calibrated in retardation. 

Figure 9.8 Babinet compensator which consists of two quartz wedges with crossed optical axes.

Amore useful version of the quartz wedge, shown in Fig. 6.28, comprises a graduated wedge and a flat mineral plate having the opposite sign of the optical birefringence. The path difference created by one is exactly compensated by that created by the other at the zero mark. 

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