# Parabolic lens

Collimation and focusing using parabolic lenses

In the `examples/parabolic_lens_collimation.py`

example, we create a collimated phonon flux by reflecting phonons from a parabolic surface. The figure below illustrates the concept:

We place the parabolic boundary at the bottom and move the hot spot that emits the phonon to *y* = 300 nm, as shown in the input file:

Note that `angle_distribution="uniform"`

because we need to emit phonons in all directions evenly. This model produces the following structure, which collimates phonons after reflection from the parabolic boundary:

The parabolic lens can also be inverted and placed at the top as follows

Here, the source is place in the bottom, while parabola at the top.

### Reference

Singh et al. Applied Physics Letters, (2023)

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