© 2007-2012 Thorlabs GmbH
33Operating Instruction
saturated for small beams at the lower mW levels. Use an external attenuator in that
case.
During operation keep in view the on the error window at the bottom. Care about the
'Power too low', 'Power too high' and also 'High Ambient light level' error and find a
way to correct the power level accordingly. See Measurement Warnings and Errors
chapter for details.
Example Measurements
The following picture illustrates a very simple example measurement that should
establish understanding of what a wavefront is and how it can be influenced.
a) A collimation lens (e.g. bi-convex) positioned at the distance f (its focal length)
from a single-mode fiber end face will generate an exactly parallel beam with a
plane wavefront.
b) A movement of the lens towards the fiber end (or even removing the lens)
generates a slightly divergent beam which increases in diameter on the way to
the Wavefront Sensor. Since the speed of light is the same for all rays within a
beam, the wavefront at the outer area falls back behind the center rays. The
wavefront is displayed spherical convex, the appropriate Zernike term 'Defocus'
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