# Astronomy green vs blu ray question



## iemand (Jan 3, 2009)

Hi all,

I am an amateur astronomer and I and some friends use 5 mW green pointers for aiming our telescopes. We are very happy with these, however we experience the DPSS greenies to die after a while at below freezing temperatures. It happens because the optical train gets out of collimation due cold shrinkage. Baseline : we can't target our telescopes when it freezes. It's not the batteries. Once the laser unit itself is frozen, new, warm batteries don't get it back to work.

I know a single unit diode laser would not die at cold temps. We have 2 different options : 

1° I can make us a set of 200mW reds from DVD writers that are about as visible to the human eye as a 5mW green Lpointer, but most of us are a bit nervous by the thought of using 200mW lasers at a place where several people gather, including kids sometimes. It's like waiting for an accident to happen.

2° A lower mW blu ray may be safer. I was thinking that a 10-20mW blu ray may be about as visible as a 5mW green. But I'm not sure as I've never seen a blu ray beam before... What is a minimal mW for a blu ray to give a visible beam to the human eye in the dark? 

Remember, we don't need a really bright beam. Barely visible in the dark is just fine -think the brightness of a 5mW green-. What is more important than brightness is that it doesn't die from cold.

Thanks!


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## 2xTrinity (Jan 3, 2009)

iemand said:


> 2° A lower mW blu ray may be safer. I was thinking that a 10-20mW blu ray may be about as visible as a 5mW green. But I'm not sure as I've never seen a blu ray beam before... What is a minimal mW for a blu ray to give a visible beam to the human eye in the dark?



I suspect that 20mW would probably be sufficient to match a 5mW green _in open air_ for apparent brightness. The green will still be brighter overall, but the violet (405nm) will have a greater tendency to scatter in the air.


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## Lmtfi (Jan 3, 2009)

Why not just warm the laser with an inexpensive hand warmer pack while it is being used in cold weather?


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## iemand (Jan 4, 2009)

Handwarmers are no option, due balance problems, or vibrations or whatsoever. Also, the handwarmers present continuous heating, that also affects the laser : when the diode gets to hot, it also fades.

What we need is a straighttru single unit that works when it's needed. And that is only a few secons with intervals of several minutes.


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## Antz_cro (Jan 4, 2009)

Quote

"2° A lower mW blu ray may be safer. I was thinking that a 10-20mW blu ray may be about as visible as a 5mW green. But I'm not sure as I've never seen a blu ray beam before... What is a minimal mW for a blu ray to give a visible beam to the human eye in the dark? "


Well , at this moment i am constructing a blu-ray laser from a HD DVD driver ,

And i am still waiting on the laser housing to arrive , 

i can tell you that it is a 150 Mw diode which is powerful , and it is visible to the human eye ,






([URL="http://www.keep-it-kool.com/uv_led/uvpics/UVLightSpect.jpg)"]http://www.keep-it-kool.com/uv_led/uvpics/UVLightSpect.jpg)[/URL]

i dont think visibility of the beam matters to how much output the diode emmits ( Mw) but it is more related to the Nm ( nanometers ) 

Nm ( nanometers ) is the light spectrum . Nm from 200-400 is UV ray light which we cannont see to the human eye , it is emmited from the sun 

Nm from 400 - 700 is vissible to the human eye as a different range of colours ,

And Nm onward of 700 is not vissible to the human eye and is known as IR or Infrared light which is used as signal receivers/transmitors and also is not visible to the human eye , to test IR light 

Get a remote with a little LED at th etop which is the transmitor , while the T.V is on press any button ( volume or channel ) can you see the little led light up ? 

no because it is IR and is not vissible ,

Now do the same thing but get a phone camera or any digital camera and hold it so the lens is looking directly at the LED , while the T.V is turned on HOLD any button , look at the digital screen of your camera and you should see the LED light up , this is because the phone camera does not have a IR filter .

A green laser 532Nm is more vissible than a blu-ray violet laser and a red laser as green is the most sensetive colour to the eye,

And finally , The minimum Mw for a blue-ray laser is any Mw,
The minimum you can buy is around 100 Mw ( correct me if im not correct ) as blu-ray laser diodes are only used in powerful Hd DVD drives and Blu-Ray Dvd drives.

I hope this was a help , 

thanx

Antz_cro


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## iemand (Jan 5, 2009)

I will work with the 408nm diodes from Sony PS3 with are about 20mW.

150mW bluray diodes are far to bright for our purposes. Remember we want the beam only to be barely visible.


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## NervousEnergy (Jan 10, 2009)

The LaserGlow Galileo is pretty much exactly what you're looking for.

http://www.laserglow.com/index.php?galileo

It's fairly pricey for a 5mw green laser, but it's designed to work well in cold weather and to put out a continuous beam for up to several hours using CR123 batteries with a 100% duty cycle, and uses a fixed click-on switch instead of momentary. In other words, it's designed specifically for scope mounting. 

I had nearly the exact same requirements several months ago. Unfortunately it doesn't work so hot as a hand-held pointer if you're teaching an astronomy group and need to point out specific bodies or constellations, as you can't see the beam once you get very far off-center. 30mw works well for that without being brilliant enough to affect night vision. But for a scope mounted guide pointer it can't be beat.


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## Cydonia (Jan 11, 2009)

Yes, the LaserGlow Galileo is the best bet.
For telescope aiming you should also have a reflex sight like a Telrad. It seems 7X50 sighter scopes are out of fashion these days :shrug:


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## luvlasers (Jan 12, 2009)

Why do you think single unit diode lasers will not have problems with the optical train due to shrinkage?


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## iemand (Jan 12, 2009)

Thanks for the Galileo advice!

Nevertheless, I wiil also try a bluray.



> Why do you think single unit diode lasers will not have problems with the optical train due to shrinkage?


 
Easy. A single unit diode laser (direct pumped diode laser) has no optical train (pumping crystals)


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## iemand (Jan 13, 2009)

I took a look at the galileo specs :

*Operating Temperature*15-35 C

Seemslike it won't do it that good ad -10°C either...


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## Kenom (Jan 13, 2009)

umm suprisingly your 150mw bluray is going to be pretty dim. Your problem is that your temperatures are too low for a laser to really work well. I live in Montana where the temps get very cold and I've found a few lasers that just plain won't work in the cold. However as you indicated, the direct diode will not suffer from this problem. However a 30mw bluray will not be visible to the human eye as it's almost in the range your eye cannot see. I've built literally hundreds of 100-350mw red lasers and 5-180mw blurays and the 300mw red is about as visible as a 150mw bluray and in comparision to a green is about as bright as a 5mw green (maybe a bit dimmer) Your in an area that I'm not sure can be resolved. I understand your reluctant to use a higher powered laser pointer but I honestly don't see a way of getting you the visibility that you want without increasing the power to that such as your wary of pointing at the ground with all the kids and such.

Let me think on this for a bit and I might have some suggestions that I literally can test (as the tempertures at night right now are average of -4F)


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## SemiMan (Jan 16, 2009)

Are you seriously power limited or do you have access to a reasonably size lead acid battery? I would just go with some sort of heater with a thermostat that runs it around 60-70F. Should not be too hard to rig up.

Semiman


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## Illum (Jan 27, 2009)

iemand said:


> Handwarmers are no option, due balance problems, or vibrations or whatsoever. Also, the handwarmers present continuous heating, that also affects the laser : when the diode gets to hot, it also fades.



a hardwarmer might be overkill...say, do you have a dew heater installed? you could create a new path of resistance and size the resistors to match your heating requirements.

Also, you could secure the laser in such a way that it becomes immobilized to the scope. A portable laser might post a risk but a mounted one from what I've seen doesn't seem to be a bother


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## Tachikoma (Jan 28, 2009)

As for the beam visibility, I've received my 115mw blu-ray today and tried comparing it with a 5mw green and a 200mw red: the more visible is, as expected, the green, then comes the blu-ray and finally the red.


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## alaskawolf (Jan 29, 2009)

iemand said:


> Hi all,
> 
> I am an amateur astronomer and I and some friends use 5 mW green pointers for aiming our telescopes. We are very happy with these, however we experience the DPSS greenies to die after a while at below freezing temperatures. It happens because the optical train gets out of collimation due cold shrinkage. Baseline : we can't target our telescopes when it freezes. It's not the batteries. Once the laser unit itself is frozen, new, warm batteries don't get it back to work.
> 
> ...


about -30F is when i have issues with my greenies , i use energizer E2 which are pretty good to -40F


http://www.youtube.com/watch?v=d34MtFE_2rY


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## ktafil (Feb 13, 2009)

Just a thought:
can't you put the laser in room temperature enviroment and lead the laserbeam outside through mirrors or optical fibers?


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## stefanj (Feb 22, 2009)

I had the same problems with my telescope mounted laser. I switched to LiIon powered lasers (Romisens) and the problems went away. If you can get a LiIon powered laser you might have better luck.


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