Hi all, i have a question.
If i have a green laser pointing from the top to a glass full of water, do these reflections in the water are dangerous with a 10mw laser?
Also, if anyone can clarify me the concept of spectral reflection it will be great.
spectral reflection is a reflection from a mirror like surface that preserves the laser beam with little distortion.
Diffuse reflection, aim the beam at a rough surface such as fine sandpaper, and you get the idea.
There is not a good explanation, other then experience, of where the line is between the two. It strongly depends on what the material is that is doing the diffusing,. It is possible to have a hazardous diffuse reflection, and in that case, you need to make measurements with a laser power meter to be sure. The line between class IIIB (500 mW) and Class IV 350 mW and up, is thought by many to be where diffuse reflections some distance away from the eye become hazards. In reality, you have to measure the distance to the eye and the power received.
As to your question, your looking at Fresnel reflections, and the strength of the reflection is proportional to the index of refraction of the water.. For lead glass, a similar material, the reflection is 4-5% of the incident power, so for 10 mW , would be less then .5 mW, or class IIA. Your blink reflex, will for the most part, protect you up to 5 mW or so, so the reflections will be painful, but not that hazardous.
This assumes your pointer is actually 10 mW, and the only way to know for sure is to measure it.
You can experience secondary effects though, where a unexpected bright reflection causes you to physically react, loose some muscle control, and do something like fall off a chair, or hit your head on a nearby file cabinet etc..
Your homework assignment is to read pages 1-360 of this:
http://www.army.mil/usapa/med/DR_pubs/dr_a/pdf/tbmed524.pdf
Steve
