Working out divergence?

[450nm]

I'd be grateful for any help with this. Maths' is not my strong point.
Could anyone let me know if I am working out the divergence properly?

I am placing the laser at first 2 metres and measuring the beam on the wall as 21 cm then moving the laser to 1 metre from the wall and measuring beam as 11 cm.

I'm arriving at a figure of 99.66865249116202 mRad which seems ridiculous. What am I doing wrong?

This is the calculator that I am using:-

http://www.pseudonomen.com/lasers/ca...alculator.html

Thanks -Dave

[wes]

11cm at 1 meter?

do you mean 11mm?

that's not as bad as 11cm but still it seems hella wide.

sorry that is all i can offer.

[450nm]

Just sat down with it all and had absolutely everything set wrong and measured wrong! Now got the beam right and no doubt figure will be very different. Thanks.

[Laser Ben]

It would be hard to get that as it is a higher divergence then the output of the diode it's self!

[The_Doctor]

What I do is measure the distance to a projected spot, at around 6 to 10 metres, and also the width of the beam at that spot, and at aperture. Once you subtract the aperture width from the spot width, you can get the divergence with trigonometry from that result and the distance to the spot.

There are gadgets you can shine a beam into from arbitrary distances and get a divergence reading from, but I don't know how those work.