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# Throwing a Beam

J

#### jangles

##### Guest
Hi I'm a total noob, I don't have a laser yet. About how far will the nova x series 15mw throw a beam?
Also lets say someone is about 500' away from me and I shine the beam at something about 10' beside them, will they be able to tell where the beam is coming from if they can't see the beam?
Thanks for all your help!
J

#### ElektroFreak

##### New member
I'd say that it should be able to project a beam around 12,000 feet without much difficulty. That doesn't mean that you'll be able to see it reflect off of an object at that distance, instead it means that you'll be able to see it reflect off of an object about 6,000 ft. away. The return trip counts as part of the total distance traveled. This is just a rough estimate, so keep that in mind. It could go much further, it could go much less.

Yes. If you shine a green laser at someone, then from their perspective it will be fairly easy to see the beam. Laser beams are mush more easily seen from in front of the laser than behind it.

J

#### jangles

##### Guest
ElektroFreak said:
I'd say that it should be able to project a beam around 12,000 feet without much difficulty. That doesn't mean that you'll be able to see it reflect off of an object at that distance, instead it means that you'll be able to see it reflect off of an object about 6,000 ft. away. The return trip counts as part of the total distance traveled. This is just a rough estimate, so keep that in mind. It could go much further, it could go much less.

Yes. If you shine a green laser at someone, then from their perspective it will be fairly easy to see the beam. Laser beams are mush more easily seen from in front of the laser than behind it.
Thanks for the quick reply! Does that mean they will see where the beam comes from even in the daytime?

#### diachi

##### Well-known member
they won't see the beam during the day, but they will see where it comes from due to beam scatter, they will see a bright light coming from where you are even if you don't shine it on them, why would you want to be shining it at or near people anyway ?

J

#### jangles

##### Guest
Diachi said:
they won't see the beam during the day, but they will see where it comes from due to beam scatter, they will see a bright light coming from where you are even if you don't shine it on them, why would you want to be shining it at or near people anyway ?

I would not shine it at people, I just want to know the peripheral limitations of such a device so as not to invade someones space.

#### wesdaman14

##### New member
jangles said:
[quote author=Diachi link=1227137113/0#3 date=1227138008]they won't see the beam during the day, but they will see where it comes from due to beam scatter, they will see a bright light coming from where you are even if you don't shine it on them, why would you want to be shining it at or near people anyway ?

I would not shine it at people, I just want to know the peripheral limitations of such a device so as not to invade someones space.

[/quote]
Yes in the day or night, if they shine the laser around you and your looking right where the beam is coming from, you will see beam and the person.

#### RA_pierce

##### Well-known member
At night, the beam of a >15mW laser or even a 5mW green laser will be visible to the person on the end of it. Even if it is dimly lighted outside (late dusk) they may still be able to see a glare from the laser even if they cannot see the beam.

However, how far the beam will travel and how far away you will be able to project a dot are different.

The typical divergence of a green laser is around 1.2mRad (milliradians). This means that the beam will expand about 1.2mm for every meter it travels.
For example: A laser with an initial beam diameter of 1mm at the aperture and a divergence of 1.2mRad would project a dot roughly 1.2 meters wide at 1km (1 kilometer = 0.6 miles = 3168 feet).
Lower divergence is ideal, however it is rare to find a laser with less than 1.0mRad divergence without additional optics. The divergence can be decreased by the manufacturer or even yourself, but that's a different topic.
With a spot 1.2 meters wide at 15-25mW, the dot may not be visible at that distance.

However, even with a beam about 1 meter across, the light will be noticeable if the observer is in the path of the beam. 15mW of green is actually pretty bright.

Another characteristic of lasers is that the beam is noticeably brighter when looking toward the source than it is when looking from or perpendicular to the source. This is because of diffraction of the laser beam off of particles in the air. This diffraction is more noticable when looking toward the source because a larger portion of the light will be diffracted in the direction the beam is traveling. The beam is least visible when viewed at a right angle because the fewest photons will be diffracted in a perpendicular direction.
For more information on this, look here:
http://en.wikipedia.org/wiki/Raleigh_scattering

I hope this helps to answer your question. Sorry for the length, but many aspects of lasers cannot be explained in just a couple sentences or even with a simple yes or no.
Have fun reading here and welcome