Large phase shift of spatial solitons in lead glass

The phenomenon of the large phase shift of the strongly nonlocal spatial optical soliton was predicted by Guo et al. within the phenomenological framework [Q. Guo, et al., Phys. Rev. E 69, 016602 (2004)], but has not been experimentally confirmed so far. We theoretically and experimentally investigate the large phase shift of that propagating in the lead glass. It is verified that the change of the optical power carried by the optical beam about 10 mW around the critical power for the soliton can lead to a {\pi} phase shift, which would be of its potential in the application of all-optical switchings.