The probabilitiy distribution density of random values of squared   functional on Wiener process trajectories
  On the basis of the Kac formula of the characteristic function of the random variable defined by values of the quadratic functional $J_T [w]$ on trajectories of the standard Wiener process $\{w\}$, the method of its distribution density is proposed. 
Yu.P. Virchenko, N.N. Vitokhina