From: luweitest@address.invalid   
      
   On 2015-10-20 9:40, Joe Gwinn wrote:   
   > In article , Lu Wei   
   >  wrote:   
   > ...   
   >> Thanks for the advises.   
   >>   
   >> Blocking unwanted beam was the first method I tried, and the result was   
   >> sort of weird. First it's not easy to determine the edge of the laser   
   >> spot, and the two beams distance is only wide enough in a small range of   
   >> incident angle; Second even if I think I have correctly blocked the   
   >> back-reflected beam, the result ellipse graph is not like normal. Maybe   
   >> there is some diffraction effect at the edge of blocker that changed   
   >> polarity state?   
   >>   
   >> Index matching with another layer of rough backside or absorbing black   
   >> material is an excellent idea. My substrate is high transmission glass,   
   >> soda lime based I think. I will seek for a provider if I have large   
   >> quantity of samples to measure. For the time being I could live with   
   >> rubbing it by hand. Chemical etching with HF solution cannot give enough   
   >> roughness I guess, and I'd rather keep from HF if there's other options.   
   >   
   > One can buy etched soda-lime glass commercially.  Why not just use that?   
   >   
   Because I also need to measure transmission spectrum of the sample,   
   which need the glass to be flat on both sides.   
      
   > Alternately, put a drop of index-matching fluid between your soda-lime   
   > glass sheet and the polished side of a piece of commercial frosted   
   > glass - the interface  will vanish optically.   
      
   That's a good idea, I will do it if there will be too much samples to   
   measure. Thank you.   
      
   --   
   Regards,   
   Lu Wei   
   PGP key ID: 0x92CCE1EA   
      
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