This can be expressed in terms of the experimental parameters, Edcmax
and K where
Edcmax = (Ro2 + So max2) (6.7)
and K = Ro2/So max2.
Edc max is the maximum average exposure and K, frequently called the
beam balance ratio, is the ratio of the reference to signal beam
intensities. In terms of Es and Ebs these become
Edcmax = 1/2 (Es + Ebf) (6.8)
and
K = [(Es1/2 + Ebf1/2)/(Es1/2 Ebfl/2)]2
Under these conditions, the maximum amplitude of the diffracted signal
is given by 1/4(Ts Tbf). For all values of s(p) less than smax the
diffracted signal will be proportional to s(p), as desired.
The Hurter-Driffield model, although the most common in
photographic work, is not directly applicable to holography.
Transmittance, the ratio of transmitted amplitude to incident
amplitude, is the fundamental parameter in holographic filters.
Plotting the transmittance vs. exposure is more convenient than
inferring the information from the D-log(E) curve. The model as
expressed in equation 6.4 assumes the response is piece-wise linear
with two breakpoints. This neglects the smooth non-linearity which
exists throughout the film response. Although easier to analyze, the
piece-wise linear model does not predict the non-linear effects in the
regions near the breakpoints. To predict more accurately this non-