ThinLens¶

An ideal thin lens: a zero-length paraxial kick with independent horizontal and vertical focal lengths. Used for quick optics sketches, idealised matching sections, and as a stand-in for any focusing device you don't want to model in detail.

TL;DR¶

from linac_gen.elements.thin_lens import ThinLens

lens = ThinLens(name="L1", fx=2.0, fy=-2.0)   # focal lengths in metres

The kick is the textbook paraxial thin-lens map:

Δx'[mrad] = -x[mm] / fx[m]
Δy'[mrad] = -y[mm] / fy[m]

Positive f converges, negative f diverges, and the default float('inf') means "no focusing in that plane".

Tutorial¶

A ThinLens is a ThinKickElement: zero length, one kick at a single s-position. Common uses:

Back-of-envelope optics — build a doublet or telescope from two thin lenses and drifts before committing to real quadrupole gradients.
Idealised matching — insert a thin lens where a future magnet will sit and let the matcher solve for fx / fy.
Einzel-lens / solenoid stand-in — set fx = fy for an axisymmetric electrostatic or solenoidal lens whose detailed field you don't have yet.

Transfer matrix¶

The linearised 6×6 matrix is identity except for the two focusing entries:

\[ M_{\text{lens}} = \begin{pmatrix} 1 & 0 & 0 & 0 & 0 & 0 \\ -1/f_x & 1 & 0 & 0 & 0 & 0 \\ 0 & 0 & 1 & 0 & 0 & 0 \\ 0 & 0 & -1/f_y & 1 & 0 & 0 \\ 0 & 0 & 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & 0 & 0 & 1 \end{pmatrix} \]

An infinite focal length zeroes the corresponding entry.

API reference¶

linac_gen.elements.thin_lens.ThinLens(
    name: str,
    fx: float = float('inf'),
    fy: float = float('inf'),
    aperture: float = 0.0,
)

Parameter	Default	Units	Notes
`name`	(required)	—	identifier
`fx`	`float('inf')`	m	horizontal focal length; `inf` = no horizontal focusing
`fy`	`float('inf')`	m	vertical focal length; `inf` = no vertical focusing
`aperture`	0.0	mm	round-aperture radius; 0 = no check

Source¶

linac_gen/elements/thin_lens.py:31

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