Theory of Z -scan measurements using Gaussian-Bessel beams

We report a theoretical study of the Z-scan technique using Gaussian-Bessel beams. First we find that even the slightest deviation from a perfect Gaussian beam can change the sensitivity of the measurements significantly. Second we demonstrate that the propagation of Gaussian beams modulated by a small Bessel profile can increase the Z-scan sensitivity---obtained using conventional Gaussian beams---by a factor of 40 and more.