Difference between revisions of "Spatial filter"
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The spatial filter is a device such as a pinhole used to eliminate transverse modes. | 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. | ||
[[Image:Spatial coherence pinhole.png|thumb|300px| ]] | [[Image:Laguerre-gaussian.png|thumb|right|Cylindrical transverse mode patterns TEM(pl)]] | ||
A pinhole selects for the central TEM<sub>0</sub> mode and blocks all the others. | |||
[[Image:Spatial coherence pinhole.png|thumb|300px|Coherent wavefront also have transverse waves which are elimnated by a pinhole. ]] | |||
The result is a clean gaussian distribution of beam power across the cross section. | |||
[[Image:Laser gaussian profile.svg|thumb|300px|A gaussian power distribution ]] | |||
Revision as of 12:37, 26 May 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.
The result is a clean gaussian distribution of beam power across the cross section.
