From: luweitest@address.invalid   
      
   Recently I measured the reflectance of a soldering ribbon, which is Cu   
   covered by a layer of Sn (about 20μm). The device used is integration   
   ball, calibrated using polished Si wafer's reflectance as reference. The   
   reflectance curve is as this:   
      
   https://postimg.org/image/a5jikl5rv/   
      
   To my surprise there are two valleys at 769nm and 811nm. Is that normal?   
   I think Sn should not have these two valley points. What could be the cause?   
      
   --   
   Regards,   
   Lu Wei   
   PGP key ID: 0x A12F EF75 92CC E1EA   
      
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