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Old 12-29-2014, 09:50 AM #1
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Default lasers, reflection by water surface

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).


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Old 12-29-2014, 01:37 PM #2
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Default Re: lasers, reflection by water surface

It would help if you could further elaborate on what you are using it for, but I don't think you will be able to find a laser that is 100% reflected by a clear medium.
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Old 12-29-2014, 04:45 PM #3
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Default Re: lasers, reflection by water surface

Thanks very much for your reply. I attach an image of what we would like to get. lasers, reflection by water surface-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 5C) 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?
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Old 12-29-2014, 05:48 PM #4
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Default Re: lasers, reflection by water surface

Well, it depends on your budget, but there are a few suggestions I would make. Either a green diode (extremely expensive, but less temperature sensitive than a DPSS), an Osram blue diode at ~200mW 450nm, an Osram diode at 1W 445nm. I'm not quite sure though, so it'd be worth getting a second opinion.
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Old 12-29-2014, 06:27 PM #5
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Default Re: lasers, reflection by water surface

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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Last edited by olympus mons; 12-29-2014 at 06:35 PM.
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Old 12-30-2014, 05:31 AM #6
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Default Re: lasers, reflection by water surface

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.
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Old 01-21-2015, 10:51 PM #7
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Default Re: lasers, reflection by water surface

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.
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Old 01-22-2015, 08:54 AM #8
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Default Re: lasers, reflection by water surface

Quote:
Originally Posted by spaceman View Post
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.
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