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Kerr Lens

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Definition: a lensing effect arising from the Kerr nonlinearity

German: Kerr-Linse

Categories: nonlinear optics, physical foundations

How to cite the article; suggest additional literature

When a short optical pulse propagates through a nonlinear medium, the Kerr effect leads to a phase delay which is largest on the beam axis (where the optical intensity is highest) and smaller outside the axis. This is similar to the action of a lens: the wavefronts are deformed, so that the pulse is focused (assuming a positive nonlinear index n2). This effect is called self-focusing and has important implications for passive mode locking of lasers (→ Kerr lens mode locking) and for optical damage of media (catastrophic self-focusing). For negative n2, the nonlinearity is self-defocusing.

When a Gaussian beam with optical power P and beam radius w propagates through a thin piece (thickness d) of a nonlinear medium with nonlinear index n2, the dioptric power (inverse focal length) of the Kerr lens is

strength of Kerr lens

when considering only the phase changes near the beam axis in a parabolic approximation. This equation can be derived by calculating the radially dependent nonlinear phase change and comparing it with that of a lens.

The equation shows that for a given optical power Kerr lensing becomes more important for stronger beam focusing: this increases the optical intensities and even more so the intensity gradients.

Calculator for Kerr Lens

Beam radius:
Nonlinear index:
Thickness of medium:
Optical power:
Focal length: calc

Enter input values with units, where appropriate. After you have modified some inputs, click the "calc" button to recalculate the output.

See also: Kerr effect, lenses, self-focusing, laser-induced damage, Kerr lens mode locking, self-phase modulation
and other articles in the categories nonlinear optics, physical foundations

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