This chapter is more difficult to organize than others because of the great variety of requirements that a beamdivider (BD) must meet. For example, if a beamdivider design is developed with a division of 50% reflectance R and 50% transmittance T, what probability is there that the reader will find this of little interest because a beamdivider with a 30%â70% division is needed? Â§188.8.131.52 cites parameters that specify the performance of a beamdivider as:
(1) Whether the coating is nonimmersed or immersed. In Â§184.108.40.206.1 it is noted that immersed coatings usually manifest no small amount of polarization splitting.
(2) The range of angle of incidence and spectral region over which it must function.
(3) The amount of polarization, by which is meant that the p transmittance is much higher than the s. The amount of polarization of the output beam is often irrelevant, as when the input light is randomly polarized and the receiver (such as the human eye) of the reflected light from the beamdivider is insensitive to polarization. As compared to the coatings in the category (4) below, these are easier to produce.
(4) In another class of beamdividers, both the degree of polarization [see Eq. (1-5c)] and the differential phase shift (see Â§2.3.4) are to be controlled.
It is natural that the subject of polarizers appears in this chapter, because both beamdividers and polarizers function at nonnormal incidence.
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