betterbionics
newbie
Reged: Jun 15 2008
Posts: 6
Loc: Georgia
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Want to display a cross line "target" with a laser at 8 feet. When I move forward I want the cross line to shrink. When I backup I want it to enlarge. In shopping for a laser module, what laser characteristics should produce this diminishing and growing effect?
I suspect we want a laser with high beam divergence, which in other cases is usually undesirable.
How can one increase or disperse the beam? You hardly ever hear that question.
Edited by betterbionics (Tue Feb 24 2009 08:41 PM)
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Dave Johnson
hall-of-fame
Reged: Jun 03 2005
Posts: 2302
Loc: Thornton, CO
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I think any line or cross hair pattern laser will diverge. I'd suggest a green laser over a red one, for easy sighting. Here is one commercial source for such a laser. There must be many more.
Green Laser with Cross Pattern
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David Johnson, PE
www.discovercircuits.com
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betterbionics
newbie
Reged: Jun 15 2008
Posts: 6
Loc: Georgia
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Forgot to say ultimately we need an ir one. Sorry about the "red" part. Several that i saw has line lengths of ~.4 x D (working distance). At 8 feet = D, line length would be crazy big. We would need a fraction of that.
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Dave Johnson
hall-of-fame
Reged: Jun 03 2005
Posts: 2302
Loc: Thornton, CO
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You will need to look around for this. You can't make such optics easily.
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David Johnson, PE
www.discovercircuits.com
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betterbionics
newbie
Reged: Jun 15 2008
Posts: 6
Loc: Georgia
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Couldn't I just pass the laser mentioned above with a .4xd size through a 1000 um aperture and clip it without significant decibel loss?
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Dave Johnson
hall-of-fame
Reged: Jun 03 2005
Posts: 2302
Loc: Thornton, CO
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I don't think you can do this yourself. The actual laser emits light from a tiny spot on a semiconductor chip. It diverges rapidly in a asymmetrical pattern. Two clear lines, crossing in the middle, held in front of the laser will produce a pattern, but will be quite weak in intensity since very little of the light launched by the laser will spill into the two lines. A properly designed optical lens for a cross pattern is very small, so less light is lost.
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David Johnson, PE
www.discovercircuits.com
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betterbionics
newbie
Reged: Jun 15 2008
Posts: 6
Loc: Georgia
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If I have 2 laser dots on a wall. Both 3mw class 3a. I am 5 feet away. Is the safety risk cumulative or as high as the highest laser rating of the two in use?
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Dave Johnson
hall-of-fame
Reged: Jun 03 2005
Posts: 2302
Loc: Thornton, CO
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You may have to get a official FDA ruling on this. But, since the two dots don't overlap, I think you will be OK with it as a single 3mw laser. I've had to get some FDA rulings on much higher lasers (20mw), pulsed in such a way that the average power is very low.
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David Johnson, PE
www.discovercircuits.com
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