Use of SiC in a High Power Spatial Filter for Stray Light Reduction

Thomson scattering measurement of the electron temperature and density profiles in high temperature plasmas is a well established experimental technique. The existence of high levels of laser-line radiation (“stray laser light”) in the detected scattered light signal can lead to difficulty in system calibration.

Spatial filtering is a standard technique for improving the spatial profile of low-power laser beams. Focusing a beam through a pinhole aperture allows removal of spatial irregularities caused by nonlinear effects of amplification, dust or imperfect optics.

Silicon carbide is often used as an aperture material due to its high damage threshold.
Lenox Laser, Inc. of Glen Arm, Maryland, has laser drilled 210 micron apertures in SiC disks for such applications as stated above.  Experiments have shown that SiC apertures perform better than copper apertures.  It was found that the steady state stray light level for SiC was significantly less than for Cu.  Thus a silicon carbide aperture performed better than copper for irradiance at the spatial filter focus.

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