# Nonlinear Self-focusing

This BeamLab demo shows a high-power Gaussian beam incident on a block of fused silica where it then converges to a small spot due to the self-focusing effect by taking into account the nonlinear change of the intensity-dependent refractive index.

**BeamLab demo: **selffocusing.m

The following video shows how the intensity distribution changes along the propagation distance *z*. The left figure shows the two-dimensional intensity distribution *I*(*x*,*y*) normalized to the input intensity and displayed on linear scale. The right figure shows a three-dimensional view of the intensity dependent nonlinear refractive index.

Video of intensity profile (left) and refractive index (right)

After the calculation has finished, the intensity distribution as a function of propagation distance *z* is plotted. The figure below depicts the intensity distribution *I*(*x*,*z*) at *y* = 0 µm. The white line indicates the start of the block of fused silica.

Intensity distribution of the self-focusing Gaussian beam (*x*–*z* slice)

The following figure shows a compact three-dimensional view of stacked plots, each portraying the intensity distribution *I*(*x*,*y*) at different distances *z*.

Intensity distribution of the self-focusing Gaussian beam (stacked *x*–*y* slices)

## About BeamLab

BeamLab is an award-winning set of simulation tools for beam propagation through optical devices and waveguides in your familiar MATLAB^{®} environment. It offers a high flexibility in waveguide design and post-processing of any output data.