Intensity clamping of a femtosecond laser pulse in condensed matter

We measured the supercontinuum spectrum of an intense femtosecond Ti:sapphire laser pulse propagating in condensed optical media (water, chloroform and glass), at various input laser energies, below and above the threshold for filamentation of the laser pulse. It is found that the maximum positive frequency shift of the supercontinuum spectrum remains constant at pulse energies that generate single and mutiple filamentation. The constant shift is due to clamping of the peak intensity inside the filaments. (C) 2002 Elsevier Science B.V. All rights reserved.