Short range laser pointer

[cowbell]

What power of laser pointer would be safest and least noticable from the air and a distance.

I was thinking of red because it will be less noticable than green or blue and red comes in lower powers generally.

I dont want to get in trouble due to airplanes (we get lots of private helicopters around here) so looking for  one that can project a few meters but enough for me to see along it.

[crashtestdummy]

Tbh you would be better off with a rdf or telrad as you are tempting fate if you have lots of local air traffic.

[cowbell]

Tbh you would be better off with a rdf or telrad as you are tempting fate if you have lots of local air traffic.

I have a RDF, the laser would be to assist with polar alignment.

[Astrobits]

Your eyes are very insensitive to red ( and blue ) at night. Only the green have a clearly visible beam.

There are regulations on using green lasers within certain areas around airports. A call to the nearest air traffic control should clarify your options.

Nigel

[cowbell]

Your eyes are very insensitive to red ( and blue ) at night. Only the green have a clearly visible beam.

There are regulations on using green lasers within certain areas around airports. A call to the nearest air traffic control should clarify your options.

Nigel

That is the reason I was looking at red, so other people far away wont see it but I would.

[crashtestdummy]

that's the reason we use red torches,your eyes don't get blinded by them at night due to how your eyes see red.as astrobits says,you would need a really powerful red laser to see it at night

[cowbell]

that's the reason we use red torches,your eyes don't get blinded by them at night due to how your eyes see red.as astrobits says,you would need a really powerful red laser to see it at night

My red torches must be invisible then.

[PeterW]

Red don't work. Green are only visible within a few meter radius of you... Those further away won't see anything. As with all lasers, be cautious, be safe. Low power green 5mW will be fine, the cold will probably dull the batteries anyway and make it dimmer.

PEterW

[Ant]

Why would you want to use a laser pointer for Polar Alignment?

[cowbell]

Red don't work. Green are only visible within a few meter radius of you... Those further away won't see anything. As with all lasers, be cautious, be safe. Low power green 5mW will be fine, the cold will probably dull the batteries anyway and make it dimmer.

PEterW

Which is exactly what I want, a few meters. Not 200 meters into the sky then a CAA report. We have low flying helicopters from neighbours here.

[cowbell]

Why would you want to use a laser pointer for Polar Alignment?

Free will.

[crashtestdummy]

My red torches must be invisible then.

Did anyone say red was invisible??????

Anyway,enjoy your free will

[cowbell]

Did anyone say red was invisible??????

Anyway,enjoy your free will

No but being treated like I know nothing is just arrogant and also when I come on asking a simple quesiton I get "why do you want that" "why do this"...

[Astrobits]

Red is not invisible to the dark adapted eye, provided there is enough of it. Your red torch scatters a lot of it's light from the torch components and whatever it is shining on, ( book, telescope, ground etc ) so those are visible but you don't see the actual beam between the torch and subject because the atmosphere scatters very poorly and there is insufficient to stimulate your retina. The retina is much more sensitive to Green light and can see the light scattered by the atmosphere. However, if you are in the line of sight of the beam, i,e, in an aircraft you will see any colour laser up to several miles away. The danger with many Green lasers is that they also emit a lot ( several times the listed power of the laser ) of Infra-Red light which can damage the retina, not good if you happen to be flying an aircraft at the time.

Nigel

[cowbell]

Red is not invisible to the dark adapted eye, provided there is enough of it. Your red torch scatters a lot of it's light from the torch components and whatever it is shining on, ( book, telescope, ground etc ) so those are visible but you don't see the actual beam between the torch and subject because the atmosphere scatters very poorly and there is insufficient to stimulate your retina. The retina is much more sensitive to Green light and can see the light scattered by the atmosphere. However, if you are in the line of sight of the beam, i,e, in an aircraft you will see any colour laser up to several miles away. The danger with many Green lasers is that they also emit a lot ( several times the listed power of the laser ) of Infra-Red light which can damage the retina, not good if you happen to be flying an aircraft at the time.

Nigel

Exactly.  Red laser is coherent light and quite visible but not as glaringly visible as other wavelengths.

That is exactly the reason I am looking a low powered red laser but not one to burn the ass of an astronaut or annoy my neighbours flying by.

[Digz]

No but being treated like I know nothing is just arrogant and also when I come on asking a simple quesiton I get "why do you want that" "why do this"...

Cowbell, please see this from other users perspective as well.

People have been offering advice on your query only to be met with one line, arrogant replies treating them like they know nothing. They have offered reasonable responses to help answer your query.

You have asked a question and been furnished with, very reasonably, responses, all of which you have dismissed.

[cowbell]

Cowbell, please see this from other users perspective as well.

People have been offering advice on your query only to be met with one line, arrogant replies treating them like they know nothing. They have offered reasonable responses to help answer your query.

You have asked a question and been furnished with, very reasonably, responses, all of which you have dismissed.

My question was what power goes how far, I got every answer but that.

You can keep your elitist board.

[Ant]

Free will.

Charming. Remind me to never reply to you again.

My question was perfectly reasonable, and for the record I still cannot work out why a laser pointer would be any use for Polar alignment. But Hey Ho - it must be a secret.

[callump]

My question was what power goes how far, I got every answer but that.

Laser light from a 1mw red laser will go just as far as a 1mw green laser (to an adequate approximation) - and a red laser is just as likely to dazzle a pilot at night as a green laser, when shone into the cockpit (dazzle is the main danger to pilots - not eye injury).

The beam you see is just from scatter in the particles in the air - the eye is more sensitive to green light than red light, so the apparent beam will appear to go further, But the beam does not stop where you can't see it any longer - it will keep going until it hits something... A few of those photons will heading to infinity.

It is true that dim red lights help preserve dark adaptation - but a bright red light will wipe out your dark adaptation just like a white light, if it is bright enough...

/callump

[Astrobits]

Sorry Callump, you're wrong on one point. Because green lasers use an infra-red source laser the escaping I-R CAN damage the retina. There is a standing order for US Airforce pilots that if they are flashed by a laser they must immediately land and get their eye's checked out. Dazzle will pass in a few minutes, eye damage will not.

http://www.nytimes.com/2011/03/01/health/01laser.html?_r=0

There is also a mis-understanding that all lasers are coherent. The laser diodes used in laser pointers do not produce a coherent beam, unlike the lasers generated with gasses ( Helium/Neon ) as used in checkout scanners and scientific equipment.

Nigel

[crashtestdummy]

No offence but you stated you were in an area where there's lots of air traffic so tbh it's plane(fnar fnar) stupid to use any laser.end of imho.good luck with whatever you do but if you don't like people giving oppinions then don't bother asking for them!!!

[Zakalwe]

 for the record I still cannot work out why a laser pointer would be any use for Polar alignment.

When I had my EQ6 I used to use a green laser pointer to help to line up to Polaris. Peering through the polarscope invariably kneeling on damp cold ground and trying to identify which star was which was a pain in the bum. I started off by hand-holding the pointer against the mount body and pointing it at Polaris. It made the initial alignment a lot easier when squinting through the polarscope. I ended up making a little bracket to hold the laser against the mount body. Dead quick and easy, and it saved getting the wrong star in the polarscope (done that a few time!)

I've heard of people shining the laser through the polarscope to get a rough alignment. That never worked for me TBH.

I still use a laser pointer to do star alignment. I'm super-conscious of using it if I see planes in the sky though. I'd certainly think twice if I lived under an airport flight path.

[Ant]

Fair enough, never heard of it being used that way hence the question. 

I do agree that getting on your hands and knees is a pain in the butt. Especially when the grass is wet...

Ant 

[callump]

Sorry Callump, you're wrong on one point. Because green lasers use an infra-red source laser the escaping I-R CAN damage the retina. There is a standing order for US Airforce pilots that if they are flashed by a laser they must immediately land and get their eye's checked out. Dazzle will pass in a few minutes, eye damage will not.

http://www.nytimes.com/2011/03/01/health/01laser.html?_r=0

There is also a mis-understanding that all lasers are coherent. The laser diodes used in laser pointers do not produce a coherent beam, unlike the lasers generated with gasses ( Helium/Neon ) as used in checkout scanners and scientific equipment.

Nigel

Well yes - there can be IR leak, but a UK sold Class 1 CE marked laser pointer should have no IR leak. There should be an IR filter to remove the IR.

All bets are off with anything that is bought on Ebay and imported from Hong Kong...

I have read a paper that metasured he coherence length of a green laser pointer to be more than 25m  (that was a lower limit of the measurement - they did not have enough space to measure it), A multi-mode HeNe laser typically is 20cm coherence length - single mode is 100m or more...

I had always assumed they used laser diodes in checkout scanners these days, but I don't really know - I find it hard to imagine that they do use he-ne lasers these days.

/callump

[Astrobits]

Thanks, Callump. It looks like I was wrong on the coherence of green laser pointers.

I have just googled and found a paper on using a green laser pointer in an unequal beam Michelson interferometer which shows that you are correct that there is coherence to at least 25 meters with the laser pointer that they used. Further investigation shows that red laser pointers can have very variable coherence lengths from nanometers to meters . I don't know if this will apply to green lasers but as I am planning to make an unequal path interferometer I will try my green laser pointer as the light source.

You are also correct in that the green laser pointers SHOULD have an IR filter. Unfortunately many ( particularly the cheap ones ) either have very ineffectual ones or none at all. Even the best IR filters still allow some IR light through and tests on a single supply of those typically sold for astronomy showed great variation in their power output despite the label on the unit.

As for the lasers used in checkouts, there are many options using solid state lasers for these and I doubt that HeNe is used for this application, I only used HeNe as an example of a long coherence length laser.

Nigel