> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of YES NOPE9
> Sent: 25 April 2010 23:30
> To: Microcontroller discussion list - Public.
> Subject: [TECH] : two ways to skin a cat ( or laser sensor )
> 
> 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.

Depending on laser power, beam spread etc. you might be able to use one
of the IR laser 'cards' that convert IR light to visible light.  We use
these for aligning lasers on optical benches. e.g.

http://www.cnilaser.com/infrared%20viewer.htm


Also have you checked the responsivity of the IR photodiodes at visible
wavelengths?  They might still be useable with reduced output.

Regards

Mike

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