by Joe Farina » Sun Oct 16, 2022 1:32 pm
Today I noticed something, and was wondering if anyone can explain it.
I put a spatially filtered laser beam (spread with 40X objective) on a white screen. Speckle is very strong. A diffusion screen was placed before the white screen, and while my hand was holding the diffusion screen (and it was in motion) the speckle was basically eliminated. When the screen was resting on the table (no motion for the screen) the speckle returned, almost completely, with little or no reduction. Ok so far.
But, with the above in place on the table, I took a piece of ordinary clear glass (or clear acrylic) and placed it in front of the stationary diffusion screen, and moved it rapidly back and forth (or up and down) with my hand, and it eliminated the speckle. So, the presence of a rapidly moving piece of clear glass or acrylic in front of the (stationary) diffusion screen will eliminate speckle. (To clarify, the spread beam goes through the moving clear glass, through the stationary diffusion screen, then to the white screen.)
This can be easily verified by anyone who has a spread laser beam showing speckle on a surface, with a stationary diffusion screen, and a rapidly moving (by hand in the air) piece of glass or acrylic. Do inhomogeneities in the glass or acrylic cause this?
Today I noticed something, and was wondering if anyone can explain it.
I put a spatially filtered laser beam (spread with 40X objective) on a white screen. Speckle is very strong. A diffusion screen was placed before the white screen, and while my hand was holding the diffusion screen (and it was in motion) the speckle was basically eliminated. When the screen was resting on the table (no motion for the screen) the speckle returned, almost completely, with little or no reduction. Ok so far.
But, with the above in place on the table, I took a piece of ordinary clear glass (or clear acrylic) and placed it in front of the stationary diffusion screen, and moved it rapidly back and forth (or up and down) with my hand, and it eliminated the speckle. So, the presence of a rapidly moving piece of clear glass or acrylic in front of the (stationary) diffusion screen will eliminate speckle. (To clarify, the spread beam goes through the moving clear glass, through the stationary diffusion screen, then to the white screen.)
This can be easily verified by anyone who has a spread laser beam showing speckle on a surface, with a stationary diffusion screen, and a rapidly moving (by hand in the air) piece of glass or acrylic. Do inhomogeneities in the glass or acrylic cause this?