Old 09-27-2007, 12:57 AM #33
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Default Re: Core's divergence?

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Originally Posted by Orr3
When I measured my Core I also got .3 mRad.
ya that's weird, i deffinatley don't think it would be that low!?


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Old 09-27-2007, 09:16 PM #34
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Default Re: Core's divergence?

The wider the initial source, the lower the divergence can be. The CORE's beam is fairly wide at aperture, if I remember correctly.
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Old 09-28-2007, 12:12 AM #35
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Default Re: Core's divergence?

I don't know if anyone's said this yet, but it can be useful: 1 mrad is equal to about .06 degrees. So you can use this to visualize things better since most people can't visualize radians.
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Old 09-28-2007, 12:56 AM #36
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Default Re: Core's divergence?

Radians are very easy to visualize really... 1 radian is as wide as you are distant from the wall you project someting on*. This easily converts to greater distances and smaller spots too. 1 mrad at 10 meters will yield a (added) spot size of 1/1000 * 10m = 1 cm. Gotta love metric

* on a circular wall, but this is close enough for practical purposes.
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Old 09-28-2007, 02:47 AM #37
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Default Re: Core's divergence?

i never thought about it that way. i'm more of a physics/calculus guy so i always think of radians in terms of pi and didn't even think about what a radian actually is :-[ Yeah, i love metric, its amazing how all the units relate to eachother. I'm disappointed the US decided not to switch over to metric.
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Old 09-28-2007, 05:10 AM #38
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Default Re: Core's divergence?

you guys need to measure over hundreds of feet with to get an accurate reading. No dpss laser with a dot size smaller than 2mm is going to get .3mrad of divergance. It's not possible. I'd believe it on a red diode laser, and that's possible because they are point emitters, so their initial size is only a slightly larger than their wavelength across and the beam is upcolliminated to hundreds of times it's original size so you get super low divergances.
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Old 09-28-2007, 04:26 PM #39
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Default Re: Core's divergence?

divergence = 2*wavelength/Pi/minimum spot size

for a gaussian beam.

For a 532 nm beam with a 2 mm minimum spot size that gives you 0.17 mRad.
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Old 09-28-2007, 04:47 PM #40
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Default Re: Core's divergence?

Quote:
Originally Posted by likewhat
divergence = 2*wavelength/Pi/minimum spot size

for a gaussian beam.

For a 532 nm beam with a 2 mm minimum spot size that gives you 0.17 mRad.
Sorry, I'm a little confused there. What units are the variables in that equation and how did you end up at 0.17mRad?

Also, by spot size you are referring to spot radius if I'm not mistaken? I think we usually talk about full angle divergence and 1/e^2 spot diameter for laser specs on the forums, so those figures end up being a bit different (by a factor of 2).
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Old 09-28-2007, 07:15 PM #41
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Default Re: Core's divergence?

I have always heard beam divergence used when referring to half angle. The minimum spot size is usually the radius of the waist at 1/e^2, I assumed most people would be measuring the diameter so I put in the factor of 2 to fix that. If you want the full angle divergence then it should be a factor of 4 on top.
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