Effective target thickness

Because of the non-uniformity of the target observed in
Section 3.3, the average layer thickness depends on the
width and profile of the beam which stops in the target. Also recall that
we have measured only the profile in the ** Y** (vertical) dimension, hence
the horizontal profile has to be assumed. The effective thickness can be
defined via

(78) |

where

(79) |

This is a quantitative measure of the non-uniformity and is useful when optimizing the vertical position of the diffuser for deposition.

Figure 6.1 illustrates the dependence of
the effective thickness on the beam parameters. The average was calculated
assuming rotational symmetry of the thickness profile, and weighted with two
different beam parameterizations (i) Gaussian beam, and (ii)
a flat top Gaussian, for which the radial intensity at the
distance ** r**,

The figure also shows the dep