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So at work we have some bent things that we want to quantify for flatness. I went looking for optical flats and monochromatic sources.

Even on my favorite source of good-but-cheap stuff (MSC Direct), all the sources appear to use helium emission. I expected there would be at least one budget source using laser diodes.

Using a laser diode and a diffuser seems like a slam dunk to me.

So -- why not? Is this because a laser diode isn't stable enough, or because the whole process is based on one specific wavelength and green laser diodes are too impractical, or is there some metrological traceability reason?

TimWescott
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  • A guy here says laser diodes aren't monochromatic enough: practicalmachinist.com/vb/metrology/… I don't really see the difference looking around and their spectra though (what little examples I can find anyways). – DKNguyen Feb 02 '22 at 20:32
  • What test setup are you aiming for? "Back in the day," I had no problem using white light systems when looking for flatness on the order of visible wavelengths. Check out "Newton's Rings" for examples of such systems. If you are trying to measure errors closer to several microns, then I can see the need for not only monochromatic but also a good flat wavefront; the latter being difficult to get from a diode laser. – Carl Witthoft Feb 03 '22 at 14:09

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