Analysis of multi-photon absorption: z-scan using ultra-short Gaussian vortex beam

We present a detailed theoretical investigation of the Gaussian vortex beam z-scan to look over multi-photon absorption. For a fixed optical pump power, the material shows less optical limiting nature in the presence of a Gaussian vortex beam as compared with a conventional Gaussian beam. In the presence of ultra-short laser pulses, the central dark core of a Gaussian vortex beam can provide a stable and accurate z-scan profile preventing thermal degradation of the sample and the contribution of other nonlinear optical phenomena. The large cross-sectional area at the beam waist with the large divergence of the Gaussian vortex beam can be used for the z-scan in the short range of propagation. Though discussed for multi-photon absorption, it may extend to single-photon absorption in the presence of multiple energy levels participating in the absorption process. (paper)