Disclosed are a method and a device for optically monitoring a running natural fiber strand. According to the invention, a light signal is sent onto the fiber strand and is emitted once again at a different point of the fiber strand surface, is received by a detector, and is evaluated so as to determine a foreign matter, thereby allowing light-guiding foreign matters to be distinguished from the non-light-guiding natural fibers.

 
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< Optically pumped semiconductor laser device

> Test method for yielding a known good die

> Method and device for measuring at least a geometric quantity of an optically reflecting surface

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