Lasers and reflection in mirrors

1. 67

   singleapleposted 11 years ago

   Lasers and reflection in mirrors
   
   If you directed a laser light into a mirror that reflected that light back into an opposing mirror that reflected the light back into itself on the original mirror (and so on, to continue indefinitely), would that light continue to reflect even after you have switched off the laser. If not, why not.

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2. 78

   nijinekoposted 11 years ago

   The short answer is no, it would not.
   
   The reasons why are multiple. I will keep the answers fairly non-technical - please forgive the loss of precision and technical accuracy in my answers as a result. I used to work in a research and development center where a large number of the scientists used lasers as part of their every day research, so I have gained a certain amount of familiarity with the physics involved.
   
   First off, most reflective surfaces are not 100% reflective. As a result there is a slight energy loss as some of the light will pass through the surface, or be absorbed by it. This is due to the fact that a laser beam transmits some of the beam's energy in the form of heat to the surfaces it strikes. This causes the laser beam to lose a little bit of energy each time it bounces.
   
   As a laser passes through an atmosphere, it excites the air particles it passes by and through, transferring energy from the laser to those particles in the form of additional heat loss. Finally, even though a laser beam is focused into a tight beam, it still radiates light - otherwise you would not be able to see it from the side. This represents another loss to the energy of the laser beam.
   
   Eventually, through these multiple methods of energy loss, the laser beam would lose cohesion and dissipate. Even if you had some theoretically perfect reflectors in perfect alignment, enclosed in a container which was holding a theoretically perfect vacuum, the radiant energy given off by the laser would be absorbed by the container and reflectors as heat and still eventually cause the laser beam to lose cohesion and dissipate.

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   1. 67

      singleapleposted 11 years agoin reply to this

      Thanks for info. I am still confused as to why the loss of light or dissipation of light, coincides with the exact timing of the laser being switched off, if the mirrors were in perfect opposition and the light was in a state of constant reflection.

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   2. 78

      nijinekoposted 11 years agoin reply to this

      The timing is not exact, actually. There is a lag due to the chemical switching nature of neurons in the brain that are much slower than the speed of light. It just looks instantaneous to us because we cannot process such small units of time.

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