[Laser] (no subject)

[KY1K]

I'd also comment..........

Comet is course grit, but possibly quite adequate for polishing.

Toothpaste that contains calcium carbonate (also known as marble) is 
even finer grit and makes a surface that is fine enough so that the 
imperfections can't be seen without magnification.

I did the rough polishing by shorting the diode leads together and 
mounting the package loosely in a drill and letting the drill do most 
of the work. Polishing by hand is the final step.

I don't think the bubble lens on the LED type packages is extremely 
accurate, so I'd expect the field of view to be less than uniform 
with lots of fuzz around the edges. Most of probably want a well 
defines field of view to keep out QRM from nearby light sources-a 
detail many might overlook.

Regards,

Art

  At 10:55 AM 3/28/2006, you wrote:
>Art - I did get a chance last evening to sand off the lens on an 
>SFH-203 detector and polish it.   There was a definite improvement 
>in sensitivity as well as narrowed field of view as you had 
>stated.  I didn't get a chance to make  quantitative measurements 
>last night  but I will do that just for the record.  The focus had 
>been mushy as one might expect from a miss match and is now more 
>definitive.  The aiming is of course more critical but that will be 
>helpful in eliminating interference from other nearby sources.   I 
>had been meaning to run that experiment for some time & appreciate 
>your comments which spurred me on to finally doing it.
>  - Kerry N6IZW -
>
>
>
>>Kerry,
>>
>>The units that come in plastic LED type packages are NOT good. If 
>>you want to use the bare diode without an external lens, they are fine.
>>
>>When using them with an external lens to collect more light, they 
>>are not good. The problem is that the package does not focus the 
>>light on the photodiode unless the light striking the package is 
>>parallel. SO, the losses are quite large when used with an external 
>>collector lens because the focal point will then fall quite short 
>>of the photodiode surface itself.
>>
>>Years ago, I worked out a procedure to correct the problem though. 
>>I ground the bubble lens away till it was flat, then polished the 
>>front surface (with Comet and water on a small piece of glass). 
>>Having a front face that is flat and relatively smooth made a lot 
>>of difference when used with an external lens.
>>
>>Regards,
>>
>>Art
>>
>>
>>
>>
>>
>>
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