On Sun, 25 Apr 2010, YES NOPE9 wrote:

> I want to point a laser at a surface that may vibrating at a high  
> frequency.
> Possibly up to 20MHz.  I want to measure the deflected signal with a  
> photodiode.
> 
> I have found fast photodiodes ( rise time = 6 nsec ) in the 800 nm  
> range for $10 USD.
> I want to be able to see the beam so that I can tell if the  
> arrangement is aimed correctly.
> 
> EITHER
> I can somehow  marry a visible beam with the 800 nm beam  ( I don't  
> know how )
> OR
> I can find a fast photodiode ( < 10 nsec , under $20 ) that senses  
> light in the visible range.
> 
> 
> Any suggestions ?

If you dont need to see the beam all the time, look for something that 
will flourece in the visible spectrum when illuminated with 800nm light 
(e.g. dye, glass, plastic).

Regards
sergio Masci
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