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# Technical annotations F-Theta-Ronar

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**Characteristics of F-Theta lenses**

F-Theta lenses have two main characteristics. When a beam is deflected by a scanning mirror in front of a lens, then the scanned distance is proportional to the scanning angle. Secondly the focus position over the entire scan field is always in the same plane.

**Basic calculations of F-Theta-Ronar lenses**

**Spot-Ø = 1.83 * λ * FL / beam-Ø**

Spot-Ø: image spot diameter [µm]

1.83: factor of apodisation

λ: wavelength [nm]

FL: focal length [mm]

Beam-Ø: entrance-beam diameter [mm]

The scan length in each direction x or y can be calculated by the formula:

**2y= FL * 2Ө _{y} * π/180 and 2x= FL * 2Ө_{x} * π/180**

2x, 2y: scan length in direction x,y [mm]

FL: focal length [mm]

2Ө_{x,y}: max. scan angle Theta for each mirror [°]

π/180: conversion factor (into radian)

The mirror distances m1 and m2 are recommended values and may vary. A smaller entrance-beam diameter allows larger scan angles and therefore larger scan fields are achievable.