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GIBSON 225

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Hi , i'm a newbie in this laser world , and i would like to get some advice of any expert that can help us to find a good combination of a laser and a beamexpander. For a scientific experiment we are looking for a laser and expander to create a strong beam with very little divergence .The beam spot has to be visible for about 6 miles or more with lowest divergence possible , hopefully about 0,1 mrad or a bit more. Any advice will be welcome !:thanks:
 

diachi

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What's the experiment? Any particular wavelength in mind? What's your budget like?
 

GIBSON 225

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Well we want to measure a long dike to see how level it is , but the dike is more than 8 miles so it probably has to be a green laser because of the visibility . It might be another wavelength but the main thing is that the beamspot will be visible after that long distance and we would like the spot te be as small as possible , not much more than 2 mtrs in diameter... budget must stay under 1500 dollars..
 

diachi

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Well we want to measure a long dike to see how level it is , but the dike is more than 8 miles so it probably has to be a green laser because of the visibility . It might be another wavelength but the main thing is that the beamspot will be visible after that long distance and we would like the spot te be as small as possible , not much more than 2 mtrs in diameter... budget must stay under 1500 dollars..
Going to need to go with a DPSS laser module, they have the best beam characteristics (Nice round spot, good divergence before the beam expander [<1.5mRad is typical] etc). I'm not sure on what power would be ideal - I personally wouldn't go for less than 500mW @ 532nm. CNI are probably your best option there. >>Link<<

As for beam expanders - you can DIY them, but the results likely won't be as good as something professionally built. I'd go with a 10x expander and be done with it - that'll be fine with an initial beam diameter of <=2mRad and divergence of <1.5mRad. Unfortunately something like that, professionally built (With AR coatings and such too) from the likes of Edmunds or Thorlabs is going to run you $700-800. >>Thorlabs<< >>Edmunds<<

You'll also need some nice mounting hardware to keep it all steady and lined up - an adapter for the beam expander and the laser module would be good if you can source one - if not, separate adjustable mounts would work. Keep in mind that the slightest wobble over at the laser end is going to result in a HUGE wobble after 6 miles (8 miles? You said both numbers...).
 
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GIBSON 225

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Thanks! I just went to Thorlabs and saw that they even have a 20x beam expander ... would that be even a better solution to keep the spot as tiny as possible? Or will the 10 x be a better solution because of some reasons ...
 

diachi

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Thanks! I just went to Thorlabs and saw that they even have a 20x beam expander ... would that be even a better solution to keep the spot as tiny as possible? Or will the 10 x be a better solution because of some reasons ...

20x will reduce the divergence even further over the 10x.

If you have a 1mm diameter beam with 1mRad divergence and you add a 10x expander you end up with a 10mm beam with 0.1mRad divergence. So the beam is expanded by a factor of 10 and the divergence is reduced by a factor of 10.

Same thing applies with 20x, except the expansion/reduction factor is 20x instead of 10x. :p
 

CurtisOliver

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Just remember to check your input and output diameter before you buy the expander. For example if you have a 20x expander, with a input allowance of 3mm and a exit of 50mm. Then the maximum input beam you can put in is 2.5mm. If you put in a 3mm beam, then you will only be able to get 16.7x. Simple, but an easy mistake to make. I don't know what beam expander you are looking at, but just keep this in mind, as most DPSS's are around 3mm in diameter. Again, don't know what laser you are getting. Just check the spec sheets. :)
 

CurtisOliver

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If you want, you can send me the spec sheets of both the expander and the laser, and i'll work out the limits for you. (Minimum spot size, max magnification etc)
You say that you want the laser to be within 2m at 8 miles (12.87 km)
If I imply that you are able to take a 3mm beam at 2mRad and expand it 20x. Then your spot size will be 1.347m wide. Mission achieved. But real life is a pain. And you will have to allow for standard stock specs, tolerance of your focusing capabilities, accuracy of specifications given by manufacturer etc. But I am willing to help :)
 
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GIBSON 225

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Thank you Diachi and Curtis , a lot of help here at this forum! We cannot afford to make mistakes in buying the wrong equipment so i am glad with all the tips and advice we are getting . I probably will buy a CNI laser (thanks diachi , looks like a trustworthy site ) but am still a bit in doubt whether to take the PGL 800MW or a DPSS because with the latter i don't know if we get enough power with it (they don't go further than 300 mw in the wavelength we need (532). And i am also in doubt to buy their own laser expander (10x) or if i will buy the laser expander with another company ( the 20x expander from Thorlabs).When we go for the first option the components will probably go well together and are 'made for eachother' , but on the other hand we would miss the extra 10 times expansion from the Thorlabs. I agree , real life is a pain sometimes :)
 

CurtisOliver

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Hi Gibson, Here is a spec sheet for a PGL-III-C-532. This range goes up to 500mW, which IMO is enough power for this experiment.
Plus the beam spec are good. http://www.cnilaser.com/PDF/PGL-III(-C)-532.pdf
At 1.5mm with 1.5mRad divergence, we should be good for a 20x expander. But if you can post the link to the thorlabs expander, please do. I can then check that it to see if it will be worth it.
 

diachi

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Hi Gibson, Here is a spec sheet for a PGL-III-C-532. This range goes up to 500mW, which IMO is enough power for this experiment.
Plus the beam spec are good. http://www.cnilaser.com/PDF/PGL-III(-C)-532.pdf
At 1.5mm with 1.5mRad divergence, we should be good for a 20x expander. But if you can post the link to the thorlabs expander, please do. I can then check that it to see if it will be worth it.

If you need longer than a couple of minutes run time I'd go with this instead of the PGL: High Stability 532nm Laser | CNIlaser

Unlimited duty cycle and it'll keep a nice clean beam the entire time too. Not to mention it's easier to mount...

Also, CNI have beam expanders - I'm sure if you talk to them they'll have something that can screw directly onto whichever laser you go for.

optics assemblies | CNI laser
 

GIBSON 225

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Thanks Diachi but i got mail from CNI in which they say our experiment will fail with the distance we need ( at least 6 miles) and that we would need a 20 Watts (!) laser to get the job done . Whats your idea about that , is it really that hard for a laser spot to reach at least a couple of miles ?
 

CurtisOliver

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steve001

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Thanks Diachi but i got mail from CNI in which they say our experiment will fail with the distance we need ( at least 6 miles) and that we would need a 20 Watts (!) laser to get the job done . Whats your idea about that , is it really that hard for a laser spot to reach at least a couple of miles ?
That's not true. What they might have been saying is you won't be able to see the spot with the naked eye. Visibility also depends upon the reflectivity of the surface.
 
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GIBSON 225

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Glad to hear we dont need THAT much , it would be very expensive too probably. But Diachi , if we would go for the high stability laser( MGL) then what power do you think we would need ? 500 mW enough like Curtis said? Or do we need extra power ( the MGL -F-532 goes up to 2500 watts ) .
 
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Don't forget that you want to see a beam spot not back scattering.
After 8 miles the beam will be a mess. (it's not a vacuum but a real hot-cold moving air. A dike - higher humidity.)

20 W - might be not very safe to operate too.
 




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