What causes the angular fringes in laser light pictures?

[papernuke]

I was reading the wikipedia page on laser light, and on a linked article, I saw this image:

http://upload.wikimedia.org/wikiped...ance_Battalion_in_"Commando"_Training_(2).jpg

What is causing those red specks to appear? I'm thinking it's the dust on the out side of the camera lens, but then why would some of the specks seem to be so in-focus? While the camera is focusing quite a few meters away.

 

[Danger]

I've never seen anything like that before. Usually, there's just a lens flare. Do you know whether it was a digital or film camera? Given the shape of those spots, I actually thought initially that it was the result of a planetarium galaxy display superimposed upon the original photo.

 

[Drakkith]

I think it's just the diffraction pattern of the laser combined with a reflection and interference effect from the multiple lenses of the camera.

 

[Bobbywhy]

papernuke, I am fairly certain the pattern around the source is called “laser speckle”
http://en.wikipedia.org/wiki/Speckle_pattern

As for the bright splotches off to the right-hand side, I’ve no idea.

 

[Drakkith]

As for the bright splotches off to the right-hand side, I’ve no idea.

I'm guessing it's internal reflections or something like that. IE laser light reflecting off the sensor, then off the glass and back onto the sensor.

 

[davenn]

The speckles are naturally visible you don't need any lenses or other optical devices
you eyes will see them quite happily.
If you get close into line with the laser light ( but not directly...for eye safety reasons) you will easily see the speckle pattern surrounding the main bright core of the beam.
I work with lasers and see this on a daily basis

Dave

 

[mikeph]

The radial peaks look suspiciously like etalon fringes, maybe inside the retina or inside/between the camera lenses. Perhaps the angular fringes happen as a result of the camera set at a very high f-stop- at this setting, the aperture (being made of overlapping blades) becomes less like a circle and more like a polygon, which causes the light to diffract along many discrete angles.

^^ all that is speculation

 

[sophiecentaur]

The radial peaks look suspiciously like etalon fringes, maybe inside the retina or inside/between the camera lenses. Perhaps the angular fringes happen as a result of the camera set at a very high f-stop- at this setting, the aperture (being made of overlapping blades) becomes less like a circle and more like a polygon, which causes the light to diffract along many discrete angles.

^^ all that is speculation

I think you're right. A bit like Newton's rings but, with more coherent light (laser), the same sort of diffraction effect can occur with much bigger path differences.