Diffraction Grating Recall!!!
At least 7,000 gratings are affected, maybe more. The manufacturer cannot tell us when the defective gratings were first incorporated. If you have received spectrographs and diffraction gratings from us during 2011, you may be affected. The defective gratings appear normal and are properly labeled (as 1000 lines/mm Linear Diffraction Grating). However, the material of which they were produced was bidirectional grating material. They essentially send a spectrum out in multiple directions, rather than the usual horizontal ones. These will not work in the Stanford spectrographs.
How to tell if you have defective gratingsIf your students have built their spectrographs, look through a few of them. If the spectrum appears on top of the spectrograph scale, your gratings are fine. However, if the spectrum appears in multiple bars on either side of, and close to, the slit, your gratings are defective.If you have not built your spectrographs yet, hold one of your gratings horizontal about 2" above a tabletop. Then shine a red laser pointer straight down through it and look for red spots on your table. If you see 2 or 3 spots in a line, your grating is fine. However, if you see a "grid" of spots, 3x3, 4x4, 5x5, etc. then you have defective gratings. How to get your gratings replacedThe manufacturer will replace all defective gratings. If you have unused gratings, please return them to us and we will replace them:Stanford Solar Center Stanford University 452 Lomita Mall, Room 134 Stanford, CA 94305-4085If you are unable to return unused gratings, or have already built your spectroscopes, then let us know how many you need to have replaced. To report gratings, please e-mail sol-ctr at sun.stanford.edu. Make sure you include the number of gratings you need and a shipping address.
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