On Wednesday, January 15, 2014 6:57:24 PM UTC-5, gghe...@gmail.com wrote:   
   > On Wednesday, January 15, 2014 10:49:26 AM UTC-5, haitic...@gmail.com wrote:   
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   > > On Tuesday, January 14, 2014 7:43:40 PM UTC-5, gghe...@gmail.com wrote:   
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   > > > On Monday, January 13, 2014 12:02:06 PM UTC-5, haitic...@gmail.com wrote:   
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   > > > > As a thought experiment, consider that an average Si PD detector is   
   somewhere around 2mmx2mm, as I remember. So the question arises in my mind,   
   has anyone cut the rather expensive filters into sizes needed for the   
   detectors? I looked around, and    
   Tungsten carbide scribe goes for $8 (seems to work better than the diamond   
   variety.)    
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   > > > > This could be done by hand, but a "scribing engine" worth   
   consideration. I'm still thinking about it, but ideal is to have tensioner   
   spring, guide for sliding, and way to immobilize the filter.    
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   > > > > What is needed for immobilization is a glue to temporarily fix the   
   filter. The dopping wax used by diamond polishers, the old standby Duco   
   cement, or Sodium Silicate, a water soluble glue. You probably dont want to   
   melt wax, or expose filter to    
   water, so that leaves Duco released with acetone. I'm even nervous with   
   acetone, since it has a hydrophilic double nature capable of penetrating   
   inorganic films. I'd feel better with a strictly hydrophobic solvent like   
   toluene, methylene chloride, or    
   hexane.    
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   > > > > Possibly someone will post that the filter manufacturers like OCLI are   
   doing this already, but given that detectors are generally small area, it's a   
   bit surprising to me that the filters are so large.    
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   > > > > JB   
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   > > > I think this is a bad idea,  Interference filters (IF) typically have   
   internal layers that don't like water, and hence a coating around the   
   perimeter.     
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   > > > So it depends on the IF, only my supplier knows for sure.       
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   > > > George H.   
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   > > I used to make these professionally, if that matters. There are several   
   designs - many layer dielectrics and metal layers with a gap between. These   
   were made by magnetron sputtering, which produces a fairly hard coating,   
   depending on the material.    
   They are generally up to being cut. You understand, this is for prototype   
   work, and production would be different. Materials vary, but high index is   
   often TiO2 and low can be MgF2. These are robust materials, as evidenced by   
   some camera filters directly    
   exposed to the ambient. In production, you might set the computer program   
   boundary conditions to index of refraction 1.33 to embed in Silicone. These   
   multilayer dielectrics are designed in computer programs, and the thicknesses   
   monitored by quartz    
   crystal oscillators inside the vacuum chamber.   
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   > Well then you most certainly know a lot more than me.     
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   > You don't want to make them less than X times the thickness.     
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   > How much smaller than 12 mm do you want?     
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   > George H.   
      
   Hi George,   
   My mispent youth - doing TF work. Thanks for your understanding. I am just   
   doing quantitative work, covering a Si Photodiode with a filter that may not   
   preserve an image, just most of the light. So the BP34 (which Phil Hobbs   
   kindly told me about), is    
   about 2.5 mm square, as I recall.    
   The bandpass filters in Edmunds optics cost over $100 for the 12-25 mm dia   
   sizes. But these filters are for the "satin underwear" crowd who don't mind   
   paying high prices for filters that maintain coherence over every square mm of   
   their aperture, a luxury    
   unnecessary in quantitative measurements.   
      
   The thickness of the bandpass designs I don't know - I'm going to make a wild   
   guess - It's 10 layers X 400 angstroms (40 nm). So that's a thickness of .4   
   micron, if my math OK. Probably low by 2-3X.   
      
   The whole thing is a thought experiment, at least to me, to just see what is   
   the minimum required for quantitative measurements in narrow bandwidth   
   filters. Depositing directly onto a Si surface another way to go.   
   JB   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)