  The large phase shift of strongly nonlocal spatial optical soliton(SNSOS) in
the (1+1)-dimensional [(1+1)D] lead glass is investigated using the
perturbation method. The fundamental soliton solution of the nonlocal nonlinear
Schodinger equation(NNLSE) under the second approximation in strongly nonlocal
case is obtained. It is found that the phase shift rate along the propagation
direction of such soliton is proportional to the degree of nonlocality, which
indicates that one can realize Pi-phase-shift within one Rayleigh distance in
(1+1)D lead glass. A full comprehension of the nonlocality-enhancement to the
phase shift rate of SNSOS is reached via quantitative comparisons of phase
shift rates in different nonlocal systems.
