C.G.S. system

All symbols have their usual meaning in the c.g.s. system of units, as given in Ref. 3. The common interpretation that the central ion sees its ionic cloud at a distance k 1 away is valid for the point-charge model only. For the DH second approximation the ionic cloud can be reduced to a charge located on a spherical surface at k 1 so as to maintain a constant potential at the surface of the central ion. Therefore, it cannot be replaced by a point charge. 

Although the bulk SHG and electrooptic coefficients, d33 and r33, are frequently quoted in pm V-1, many NLO quantities (and most of those discussed in this chapter) are typically expressed in c.g.s. units. These are not usually stated explicitly, but esu is used to denote that the units are the appropriate electrostatic units for that quantity in the c.g.s. system. We have followed this practice in this chapter. Some important conversions from esu to SI units are given in Table 11.3. In addition, we have followed the practice of quoting 2PA cross-sections in Goeppert-Mayer (GM) units, which are named after the scientist who first predicted 2PA processes [204, 205], and defined as 1 GM = lO-50 cm4 s (photon)-1. In addition, readers should note that cross-sections are sometimes quoted in cm4 GW-1 cross-sections in these units can be converted to cm4 s (photon)-1 by multiplying by the photon energy. 

Physical quantities relevant to analytical measurements and the units and symbols used to express them are given in table 1.3. Both S.I. and C.G.S. units have been included because of current widespread use of the latter and for ease of comparison with older literature. However, only the S.I, nomenclature is now officially recognized and the use of the C.G.S. system should be progressively discouraged. 

In the c.g.s. system, the capacitance is expressed in centimeters. For comparison with practical units, we note that 1 farad = 9xI0" cm. Note, however, that in Eq. 3G, C is the capacitance per unit surface area. 

In the C.G.S. system, in which the unit of length is the centimetre and the unit of force the d3me, the unit of work is the dyne-centimetre or erg. 

In conclusion, the following numerical values of natural constants may be tabulated, expressed in every case on the C.G.S. system —... 

The dimensions are referring to the three major properties of the universe the matter, the time, and the energy. Earlier, a c.g.s. system of units (centimeter, gram, and second) was in general use, but now, another system ofunits has been adopted in many parts of the world, known as SI (System International d Unites) (Table 1). 

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