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22 September 2011 Improving spatial coherence in high power lasers
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Two ways to improve spatial coherence in high power beams are considered and compared, spatial filter and adaptive optics. High power in lasers is usually produced by using a succession of optical amplifiers. As intensity increases in optical amplifiers or lasers, spatial coherence decreases because of uneven heating and other nonlinearities. Often a spatial filter in the form of a pinhole is used after each stage that will block the parts of the beam that are spatially incoherent and would scatter sideways out of the beam. The loss of light blocked by the pinhole lowers amplification so that more amplifiers are required. An alternative approach to improving spatial coherence is adaptive optics. In this case the wavefront is measured using a wavefront sensor such as a Hartman wavefront sensor or with a photonic crystal. The measurements are used to compute settings for a deformable mirror. This involves a complicated feedback loop. The deformable mirror reduces the undesirable deviations in the wavefront to improve spatial coherence.
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Alastair D. McAulay "Improving spatial coherence in high power lasers", Proc. SPIE 8134, Optics and Photonics for Information Processing V, 81340I (22 September 2011);


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