by Joe Farina » Thu May 01, 2014 3:35 pm
Dinesh wrote:Joe Farina wrote:yes, I was also wondering what Dinesh had in mind by "smoothness"
I mean that there must be no local density variations. It must be as homogenous as possible. If the local density varied by a few percent over even as small a distance as lambda/10 then it would form a scattering centre. A good demonstration of this is to fill a pint glass with water. Then shine a bright white light into it. Then add milk into it, drop by drop. Soon, a blue haze develops coming off the sides and the directly transmitted light begins to go reddish. This is due to the local density difference between milk and water. Sometimes micro-bubbles appear in the gelatin, for example, that aren't easily visible, but they form scattering centres which scatter blue to a much larger extent than any other wavelength. Sometimes you get crystal growth inside the gelatin once you add the dichromate and this too is a scattering centre.
Thank you Dinesh, I printed a hard copy of your comments in this thread for my records
At the moment, I'm using 532 and 633nm, but previously with 457nm, I did see some odd effects. In much of my reading, and in many of your posts, a rather abrupt transition is indicated, with regards to the importance of scattering effects, when blue is involved. A laser beam entering a cube of gelatin, with the scattering observed from the sides of the cube, seems like an excellent test for scattering, as you suggested. Those are interesting points about the micro-bubbles and crystal growth, thanks.
[quote="Dinesh"][quote="Joe Farina"]yes, I was also wondering what Dinesh had in mind by "smoothness"[/quote]
I mean that there must be no local density variations. It must be as homogenous as possible. If the local density varied by a few percent over even as small a distance as lambda/10 then it would form a scattering centre. A good demonstration of this is to fill a pint glass with water. Then shine a bright white light into it. Then add milk into it, drop by drop. Soon, a blue haze develops coming off the sides and the directly transmitted light begins to go reddish. This is due to the local density difference between milk and water. Sometimes micro-bubbles appear in the gelatin, for example, that aren't easily visible, but they form scattering centres which scatter blue to a much larger extent than any other wavelength. Sometimes you get crystal growth inside the gelatin once you add the dichromate and this too is a scattering centre.[/quote]
Thank you Dinesh, I printed a hard copy of your comments in this thread for my records ;)
At the moment, I'm using 532 and 633nm, but previously with 457nm, I did see some odd effects. In much of my reading, and in many of your posts, a rather abrupt transition is indicated, with regards to the importance of scattering effects, when blue is involved. A laser beam entering a cube of gelatin, with the scattering observed from the sides of the cube, seems like an excellent test for scattering, as you suggested. Those are interesting points about the micro-bubbles and crystal growth, thanks.