Difference between revisions of "Spatial filter"
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A pinhole selects for the central TEM<sub>0</sub> mode and blocks all the others. | A pinhole selects for the central TEM<sub>0</sub> mode and blocks all the others. | ||
[[Image: | [[Image:Spatial_Filter_-_process.jpg|thumb|300px|Processing of a beam to remove higher spatial frequencies ]] | ||
<swf width="500" height="400">images/7/71/Z-scanclean.swf</swf> | <swf width="500" height="400">images/7/71/Z-scanclean.swf</swf> | ||
Revision as of 08:57, 7 June 2011
A laser beam is by definition coherent with respect to longitudinal wavelengths which is determined by the length of the cavity. But coherent light can also exhibit transverse modes. A cross section of laser beam might exhibit a combination of various modes creating an uneven intensity. The spatial filter is a device such as a pinhole used to eliminate transverse modes.
A pinhole selects for the central TEM0 mode and blocks all the others.
<swf width="500" height="400">images/7/71/Z-scanclean.swf</swf>
The result is a clean gaussian distribution of beam power across the cross section. This is desirable for many optical setups such as the Femtosecond Z-Scan Spectrometer
