  In the Color Glass Condensate approach to the description of high energy
heavy ion collisions, one needs to superimpose small random Gaussian
distributed fluctuations to the classical background field, in order to resum
the leading secular terms that result from the Weibel instability, that would
otherwise lead to pathological results beyond leading order. In practical
numerical simulations, one needs to know this spectrum of fluctuations at a
proper time $\tau \ll Q_s^{-1}$ shortly after the collision, in the
Fock-Schwinger gauge $A^\tau=0$.
  In this paper, we derive these fluctuations from first principles, by solving
the Yang-Mills equations linearized around the classical background, with plane
wave initial conditions in the remote past. We perform the intermediate steps
in light-cone gauge, and we convert the results to the Fock-Schwinger gauge at
the end. We obtain simple and explicit formulas for the fluctuation modes.
