PRIMES
BeamMonitor BM+ with LDS 2.98
80
Revision 01/2018 EN
The derived beam parameter product, is a constant size as long as image defect free and aperture free
components are used.
Equation 3:
BPP
An important beam parameter is the Rayleigh length:
The Rayleigh length is the distance towards the propagation in which the laser beam has increased by
. It can be calculated by means of the following formula:
Equation 4:
23.1.2
Non rotationally symmetric beams:
In order to describe non rotationally symmetric beams, the following parameters are required:
•
the z-position of the beam waist (focus) z
x
and z
y
•
the diameter of the beam waist d
σ
0x
and d
σ
0y
•
the far field divergence angle
Θ
σ
x
and
Θ
σ
y
•
the angle
ϕ
between the x´-axis of the measuring system and the x-axis of the beam (the x-axis of the
beam is the one closest to the x-axis of the measuring system.)
Coordinate system of the beam (x, y)
Coordinate system of the device (x, y)
x-axis
y-axis
x-axis
y-axis
Fig. 23.2: Beam parameter of the not rotationally symmetric beam
All beams which can be characterized by two axes which are perpendicular to each other can be described
by means of the above mentioned parameters.
Further beam parameter such as the K-figure or the beam propagation factor are calculated directionally by
means of as the same equations as the rotationally symmetric beams. This always results in two parameters
such as Kx and Ky.
