Shekhar Guha | Searcharxiv

arXiv2010

An Effective $z$-Stretching Adaptive Finite Difference Method for Paraxial Light Beam Propagation Simulations

A new $z$-stretching finite difference method is established for simulating the paraxial light beam propagation through a lens in a cylindrically symmetric domain. By introducing proper domain transformations, we solve corresponding difference approximations on a uniform grid in the computational space for great efficiency. A specialized matrix analysis method is constructed to study the numerical stability. Interesting computational results are presented.

math.NA↗

arXiv2007

Large nonlinear absorption and refraction coefficients of carbon nanotubes estimated from femtosecond Z-scan measurements

Nonlinear transmission of 80 and 140 femtosecond pulsed light with $0.79 μm$ wavelength through single walled carbon nanotubes suspended in water containing sodium dodecyl sulphate is studied. Pulse-width independent saturation absorption and negative cubic nonlinearity are observed, respectively, in open and closed aperture Z-scan experiments. The theoretical expressions derived to analyze the z-dependent transmission in the saturable limit require two photon absorption coefficient $β_0\sim$ $1.4 cm/MW$ and a nonlinear index $γ\sim -5.5 \times10^{-11} cm^2/W$ to fit the data.

cond-mat.mtrl-sci↗