28

July 12, 1949

Saturation formulas for absorption & dispersion in the stationary state

We start with the absorption for I=1/2. The situation
to be described is that of a competition between the applied
signal & the local field spectrum, the former tending to
make the surplus number zero, the latter to
keep it at the value of temperature equilm.

The surplus number n can formally be thought of as
being distributed over a frequency range according to
a fn φ(ν)

The frequency of the applied signal {tex: $H_1 = \int H(\nu)d\nu :tex}}
is so well defined, that φ(ν) can be considered as constant
over the region where H₁ is different from zero. In the
radio frequency range such a pure sine wave for H₁ is
practically realizable. According to This signal causes
a surplus number of transitions per second