Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: nuthan.p.kamath on 31/03/2014 16:58:58
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IF i use two coherent (same phase and same frequency) sources of laser made it to intersect at a point in air ,will i get any dark spot on the that region.
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... (same phase and same frequency) ...
Have to be anti-phase to produce a dark spot, (destructive interference (http://en.wikipedia.org/wiki/Destructive_interference#Mechanism))
What you've described would be constructive-interference .
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If two laser beams converge on a a physical object, that object will get hotter than if it were hit by just one laser beam.
However, it's not possible to focus light to a "point" (in the mathematical sense) - focus down to anything less than a wavelength gets very difficult.
Note that the two lasers would need to have the same frequency and a fixed phase to cause cancellation, so some areas of the focus area may be cancelled, but other areas will have enhanced intensity.
The National Ignition Facility (http://en.wikipedia.org/wiki/National_Ignition_Facility#Driver_laser) has 192 lasers, focused on a single target about 2mm across. They use a common trigger laser so they can align all the beams in frequency, phase and timing.
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thanks for the replies guys, but do i get to see the visible point over that point
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If they intersect in transparent air, the two laser beams will pass through each other, with no cancellation - I'm afraid there will be no black spots in the air. (If the intensity gets so high that it heats the dust particles & air, the air will start to act as a diverging lens or even a plasma ball - but still no black spots in the air).
If you shine the two lasers on a reflective surface, there will be dark interference fringes.
Note: Be careful with bright lasers - you can end up with very real black spots on your retina!