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lasers, reflection by water surface

filippo

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I am searching for a laser pointer that, pointing the water surface from around 5-10 meter, is clearly reflected by water surface so that we can see and identify the illuminated dot on the water surface. It means that the laser doesn't have to penetrate the water body but has to be reflected by the surface. Of course for clear water that is very difficult, but for turbid water as water in rivers or lakes it is surely possible. Any suggestion in terms of wavelength, laser model and brand, power (it must be below 100 mW)? I am also searching something that is expected to work even in cold climate (around 0-4° degree).
 



filippo

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Thanks very much for your reply. I attach an image of what we would like to get. acqua.jpg. I cannot say too much about the project since it is scientific research. As I said we would like to buy a laser whose light is clearly reflected by water. Of course when water is very clear light penetrates below water surface (light penetration is what we don't want), but when water is turbid we have seen that light is only reflected by the water surface (reflection is what we want). However, even with turbid water there are problems due to scattering, daylight competition, etc... What we found out is that:
1)laser which are 405 nm 100 mW are reflected by water surface more compared to green and red. But the human eyes sensitivity is not too very high at that frequency therefore it is hard to see the dot during daylight hours
2)Green laser 532 nm 100 mW are too much temperature sensitive (don't work when air temperature is less than 5°C) and moreover there is a lot of scattering.
Do you have any suggestion or experience in that? Is there a laser you have tested and which light is clearly reflected by water, such as turbid water of rivers, lakes, etc?
 

olympus mons

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Do you just need to see the dot on the surface and some penetration is acceptable or can no light penetrate the surface? (not sure if the latter is possible)
How far of a distance will the viewer be from the dot?
How far away will the laser be from the waters surface?
Will the dot be in direct sunlight? What is the lighting like?
Does laser dot size and shape matter?
How long and often does then laser need to be on for?

I would agree that staying as close to the optimum visible spectrum is best. Since temperature is a factor that rules out 532nm dpss lasers so its looking like 520nm is a good choice. People can make suggestions of sellers but does this need to be a handheld portable unit or lab style laser?
 
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Alaskan

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Have you tried a wide swath of uncollimated laser light, such as from a laser diode without a lens on it, or an expander lens without collimation? Might produce some interesting reflections.
 

spaceman

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Not sure if you are still looking for an answer, but the reflection depends partly on the angle with which the light it hits the water. I can't remember if it is affected by wavelength. There is a critical angle where all or most of the light is reflected. Similar to the critical angle which causes total internal reflection in a clear glass tube (fiber optic). In general, the shallower the angle the more it moves towards total reflection. :)
 

olympus mons

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Not sure if you are still looking for an answer, but the reflection depends partly on the angle with which the light it hits the water. I can't remember if it is affected by wavelength. There is a critical angle where all or most of the light is reflected. Similar to the critical angle which causes total internal reflection in a clear glass tube (fiber optic). In general, the shallower the angle the more it moves towards total reflection. :)

Yeah mate don't bother. This guy asked questions but never stuck around for the answers. Gotta love people that waste your time.
 

Ewelyte

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I am doing some research to determine feasibility. Any assistance is greatly appreciated. I am looking for a laser that would reflect on the surface of water from distances up to 100 feet. The general conditions are as follows.

Water Clarity: clear
Water Surface: smooth to broken (wavy)
Water Temp: 68-88 F
Water Depth: 1-8 ft
Distance (source to termination): 10-100 ft
Angle (from source): 4-25 degrees
Air Temp: 65-95 F
Ambient Light: very bright; full sun exposure

Thank you in advance for your insight.
 
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Encap

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I am doing some research to determine feasibility. Any assistance is greatly appreciated. I am looking for a laser that would reflect on the surface of water from distances up to 100 feet. The general conditions are as follows.

Water Clarity: clear
Water Surface: smooth to broken (wavy)
Water Temp: 68-88 F
Water Depth: 1-8 ft
Distance (source to termination): 10-100 ft
Angle (from source): 4-25 degrees
Air Temp: 65-95 F
Ambient Light: very bright; full sun exposure

Thank you in advance for your insight.

Please indicate general catagory/type of water --water source/environment-i.e. sea water, ocean--fresh water, lake--fresh water , swimming pool .....
 

Ewelyte

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Thank you for the follow up. To keep it simple, let's confine it to Salt water/Ocean.

If anyone has input on other types of water environments, please feel free to elaborate.
 

steve001

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Thank you for the follow up. To keep it simple, let's confine it to Salt water/Ocean.

If anyone has input on other types of water environments, please feel free to elaborate.

Any visible wavelength laser will work. The experimental condition is based entirely upon the "angle of incidence". The water surface acts like a mirror.
A green 532nm dpss laser offers best visibility in bright sunlight, but do not operate well unless specially made to operate at temperatures below 70F. A green 520nm diode laser would be a second choice I think. 100 mW output should be sufficient.
 

Encap

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The wavelength most reflected by waters surface is "red", green and blue are the most absorbed wavelengths, however, what output power you would need to see a dot reflected from a distance of 100 feet, in full day light is more the question.

See, Altitude measurement using laser beam reflected from
water surface, here: http://ijeee.iust.ac.ir/article-1-42-en.pdf
 
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steve001

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The wavelength most reflected by waters surface is "red", green and blue are the most absorbed wavelengths, however, what output power you would need to see a dot reflected from a distance of 100 feet, in full day light is more the question.

See, Altitude measurement using laser beam reflected from
water surface, here: http://ijeee.iust.ac.ir/article-1-42-en.pdf

At a 10-100 foot working laid out as a specification previously at this distance an observer could stand next to the terminstion point and easily see a spot.
 

Vetttech

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The bottom line is, you would need to do some testing in real life conditions! I am guessing, you will not get the results you are looking for! Perhaps the best results would be achieved at night in the dark.
 

Encap

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I am doing some research to determine feasibility. Any assistance is greatly appreciated. I am looking for a laser that would reflect on the surface of water from distances up to 100 feet. The general conditions are as follows.

Water Clarity: clear
Water Surface: smooth to broken (wavy)
Water Temp: 68-88 F
Water Depth: 1-8 ft
Distance (source to termination): 10-100 ft
Angle (from source): 4-25 degrees
Air Temp: 65-95 F
Ambient Light: very bright; full sun exposure

Thank you in advance for your insight.

Not expensive to find out.

Get a Sanwu 304 or a couple of different wavelenght maybe a 532nm green and a 650nm red 304s for $18 to $25 depending on wavelength, test them out, and go from there.
See: https://www.sanwulasers.org/product/304green

If playing with lasers and reflected light from them-- be sure to use laser goggles to protect your eyes from damage by reflections and use safe laser handling procedures in general.

At a 10-100 foot working laid out as a specification previously at this distance an observer could stand next to the terminstion point and easily see a spot.

The bottom line is, you would need to do some testing in real life conditions! I am guessing, you will not get the results you are looking for! Perhaps the best results would be achieved at night in the dark.

Yes better chance in low or night conditions but he wants to see a reflected dot in bright full daylight.
Won't cost much to find for Ewelyte to find out if a low output power pointer reflected by seawater can be seen at 100 feet, in full 12 noon daylight.
 
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dden4012

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Headline: research submarine attacked by laser pointer. Captain said it hurt.
 

Ewelyte

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Encap ans steve001, thank you both for the suggestions and input. Laser safety and eye protection duly noted.

If cost was nearly a non-factor, which few products would you seek out for testing? I appreciate the low cost suggestions but I want to ensure that I'm not limiting your suggestions by cost.

The "spot" would need to be seen at a distance of up to 100' and in full sunlight. Also, the size of the spot reflected on the water surface can be as large as practically necessary. 3" to 3' would be perfectly acceptable.

As far as the angle of incidence is concerned, the source of the laser would be in close proximity to the viewer, within 1-10'. I have limited understanding/knowledge of angle of incidence as it pertains to optics but will educate myself on the concept today.

I was unable to get the altitude measurement using laser article to open; I'll give it a try from my computer later today.
 
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