THORLABS WFS150, Руководство по эксплуатации

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38 WFS150 / WFS150C Manual
© <2007> ... Thorlabs GmbH
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' is indicating the spherical wavefront.
c) A movement of the lens towards the light source will generate a converging
beam decreasing its diameter on the way to the Wavefront Sensor. When the
Wavefront Sensor would be replaced by a canvas, a focal point would be
seen somewhere behind the sensor position. This makes clear that the
wavefront before was also spherical but is now displayed spherical concave.
Such an example setup can be used to check the quality of optical fiber
collimators. During manufacturing the correct position of the collimation lens is
adjusted until the measured wavefront becomes flat and the calculated Zernike
coefficient Z
5
describing 'Defocus' becomes zero (Z
5
= 0). This procedure is faster
and much more precise than the conventional method using a Beam Profiler
which is moved back and forth in order to ensure a constant beam diameter.