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Why does laser light look like little particles moving about?

T

tommmtom

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Just curious, not sure if it's just me, why does laser light appear to be little particles on the surface you point it at?
Almost like a bacteria colony wiggling about?
 





I think that you see the dust in the air :)

EDIT: or on the lens
 
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Hmm could be! Try focusing to a wide beam....It's like loads of grains :thinking: It looks like that with all my lasers. Maybe it's just my eyes :rolleyes:
 
images


Speckle pattern - Wikipedia, the free encyclopedia
 
You could be seeing dirt on the lens, the diode window, or other imperfections.

Try cleaning the lens of your laser, see if that helps.
 
I think he is reffering to the individual brighter particles in the dot right? I was wondering that too.
 
It is the result of interference. It is very well documented. Cyparagon's link tells all.

Not the bubbles or mystery artifacts on the lens. Those don't "wiggle about".
 
Indeed, though a video would do it more justice then the images displayed.

The speckle pattern changes with movements of the observer or the source only as small as the wavelength, which causes it to look like its constantly changing even if you look at it sitting still.

Speckle is probably the easiest way to tell coherent light from incoherent light and requires no instruments, only your eyes to observe.
 
Benm said:
Indeed, though a video would do it more justice then the images displayed.

The speckle pattern changes with movements of the observer or the source only as small as the wavelength, which causes it to look like its constantly changing even if you look at it sitting still.

Speckle is probably the easiest way to tell coherent light from incoherent light and requires no instruments, only your eyes to observe.
Click to expand...

Thanks :)
 
Maybe we should all post words that we think of when we observe this phenomenon so that people who search will find this thread. And don't say "Just add them to the tags," because then people wouldn't make nonsensically funny posts with random words in it.


wiggly grainy jittery sandy flecks specks speckles sparkles puking glitter glimmer glint
 
Puking? :thinking:

Not sure how that would relate to lasers, or any aspect of them. Oh well.

:barf:
 
Hmm I have always referred to it as a speckle pattern on object the laser hits, and as a sparkle pattern from the beam in the air. :P
 
The phenomenon is known as "laser speckle" and the term can be searched on Wiki for those interested in knowing more about it.

In a nutshell, what you are seeing is a 2D "slice" of a complex 3D interference pattern caused by coherent laser light scattering off of a surface that is uneven relative to the laser wavelength. As you move your head (or the laser) your eyes intercept different parts of the pattern, producing the illusion of movement.

I find it rather fascinating.

T.
 
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When TS says "light" he perhaps means "beam"

Exhibit A:

DSC_8470.jpg


Dust in the air

1/400 of a second at f/1.8 at ISO 500
 
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