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Cold Underwater Laser

GreenBean

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Hello all, I am looking for a laser to help me measure underwater. There are a few downsides... it will be in 35°F (about 1-2°C) and at 100 ft deept, and this lake is quite silty (fairly bad visability). Would anyone have suggestions as to where I should look? My limited laser knowledge tells me -- higher powered green laser
Maybe 5mw or over? Also, is there a way to calculate the length of beam through various visabilities? My online searches haven't been the most successful yet. Thanks in advance! I really appreciate it!
 

diachi

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I don't have an answer for your questions per se, however, one word of advice - don't go for DPSS green (532nm). DPSS doesn't work so well when the laser is too cold (or too warm!). Look for something that is using a green diode, either 520nm or 515nm if you want green.
 

Hap

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diachi gave really great advice, 520nm/515nm would be much better then a 532nm.

On the other hand, I don't think a laser would be best for your application. Aren't there tools which measure distance? i.e you aim it at a wall and it tells you how far it is? There must be some underwater ones, no?

-Alex
 

10fenny

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Yes 520 would probably be the most visible. Yet depending on how silty it is could be your answer to how much power you will need. This could be where it could get dangerous. So do you have a sealed housing? How will you measure your distance? Divergance? What angle? any potential reflections? Sounds like a cool project. I Just want to know more.
 

Laser Chick

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Great advice given by diachi, Hap and 10fenny.

Where are you from as that will determine what can be shipped to your country.
That is the very low limit of the temperature operating range of 532nm. Be sure you get a very good quality sealed laser for that depth. Most waterproof lasers are only good to about 10 to 20 meters.
What is the approximate distance you will need to measure? I do not know of any type of data base for distance of visibility of the beam verses siltation of the water. Plus there are other variables that would be thrown into that mix. To get a measurement of just distance you will need some kind of feedback/receiver which hand held lasers do not have. How about a range finder like the ones used by bow hunters? I think they are water repellent but not waterproof though.

Welcome to the forum GreenBean :wave:
 
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GreenBean

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Thanks for the responses eveyone! I live in the states and this project will be on Lake Champlain in VT. There are a few different options for using lasers to measure distance underwater, but I am only needing them to establish 90° angles for a grid system. It may sound silly, but this is the most efficient way to create the initial boundary. (Because of the depth, we only have around 15 minutes on the bottom)

In an ideal world, I would want the beam to be able to reach a target 200ft away. But I think the particulates are going to dampen that dream... so really, if it can reach close to 50 feet I will be happy.

The two lasers I've found so far were actually reviewed in the forums a while ago... here's the link.

http://laserpointerforums.com/f52/r...-1w-445-modes-laserbtb-90467.html#post1318325

(The links to the lasers are in the OP)

I think I would be looking at the green version (the 520 as opposed to the 445) even though the 445 has a higher power... how would something like the green 120mW stack up against the blue 1W?

Also these are rated for 50m underwater. But do you think there would be a problem of the cold water not letting the laser futon properly? Or worse, the cold on the lens from the water versus the heat on the lens from the light causing the lens to malfunction - possibly shatter or crack? Should I possibly have an additional housing?

Thanks again for the help! It is greatly appreciated!
 

diachi

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Thanks for the responses eveyone! I live in the states and this project will be on Lake Champlain in VT. There are a few different options for using lasers to measure distance underwater, but I am only needing them to establish 90° angles for a grid system. It may sound silly, but this is the most efficient way to create the initial boundary. (Because of the depth, we only have around 15 minutes on the bottom)

In an ideal world, I would want the beam to be able to reach a target 200ft away. But I think the particulates are going to dampen that dream... so really, if it can reach close to 50 feet I will be happy.

The two lasers I've found so far were actually reviewed in the forums a while ago... here's the link.

http://laserpointerforums.com/f52/r...-1w-445-modes-laserbtb-90467.html#post1318325

(The links to the lasers are in the OP)

I think I would be looking at the green version (the 520 as opposed to the 445) even though the 445 has a higher power... how would something like the green 120mW stack up against the blue 1W?

Also these are rated for 50m underwater. But do you think there would be a problem of the cold water not letting the laser futon properly? Or worse, the cold on the lens from the water versus the heat on the lens from the light causing the lens to malfunction - possibly shatter or crack? Should I possibly have an additional housing?

Thanks again for the help! It is greatly appreciated!
120mW 520nm should be a little brighter than 1W 445nm - Our eyes are far more sensitive to 520nm.

The cold isn't going to be a problem with the optics - your lens won't be getting hot enough - they really don't absorb much light at all, most of the power loss is from reflections not absorption.
 
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for your question a Green laser is your option... but prepare to for out $300+..... the NDG7475 with driver at 2.4amps and g2 lens is your answer. i took my greenie out in the ocean and straight down..... the divers at deep down can clearly see the beam and dot reflection when it hit the bottom... don't forget that water bends the beam slightly. due to the refraction index....
 

diachi

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don't forget that water bends the beam slightly. due to the refraction index....

That's only if it's going from air to water at an angle though ... ;) Only a change in refractive index causes light to "bend", and then only if the angle of incidence is not >0* from normal.
 
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.......*face-palm myself*....... yh he said he going to point it at an angle..... and i thought glass is a different medium to water even if glass is in water..... stuff they never taught you at school....
 

diachi

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.......*face-palm myself*....... yh he said he going to point it at an angle..... and i thought glass is a different medium to water even if glass is in water..... stuff they never taught you at school....

Glass is a different medium with a somewhat different refractive index, but the angle from normal would be 0 degrees when the beam hits the water, or at least very close to 0 degrees so you wouldn't see much "bending". :D
 




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