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Is there currently a way to keep light reflecting indefinitely?

  1. Mar 24, 2014 #1

    Is there currently a way to keep light reflecting indefinitely such as by shooting a laser onto a perpendicular mirror then moving a second mirror into place before the light gets back to the laser?

    What is the longest? Seconds, minutes, hours?

    For the purpose of delayed choice experiments.

  2. jcsd
  3. Mar 24, 2014 #2


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    No, even the best mirrors do not reflect 100% of the incident light.
  4. Mar 24, 2014 #3
    If you'll allow me to replace "light" with "photon", then quantum electrodynamics comes to mind.
    I don't know what the record is for trapping a photon in such a cavity, but here's a link, which on page 7, claims they can demonstrate 100 milliseconds:
    But wait! I found a much better link. This one has kept photons up to half a second AND measured them hundreds of times in the process:
  5. Mar 24, 2014 #4


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    Isn't that what waveguides or optical lenses do?
  6. Mar 26, 2014 #5
    Could a combination of fiber optic cable, mirrors and lenses be used?

    Could photons be reflected back and forth multiple times to the retroreflector on the moon?

    I am trying to find the best way to keep entangled photons traveling for the longest period of time for a delqyed choice experiment.
    Last edited: Mar 26, 2014
  7. Mar 26, 2014 #6


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    Why does it have to be a long time? Can't you do a delayed choice experiment with a delay of a few nanoseconds?
  8. Mar 26, 2014 #7
    I am not sure if that is a question or an arguement. If it is question, why do you ask? How does it help answer my question?
  9. Mar 27, 2014 #8


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    The answer is no, the best cavities we can make have qualify factors of the order of 10^9; which for typicial frequencies used in cavity-QED (microwaves) means lifetimes of say a few ms.
    The lifetime for optical cavities is much shorter than that.
  10. Mar 27, 2014 #9
    Another way out if you want to keep light delayed is to work with slow light (or even stopped light). By tailoring absorption lines of a medium correctly it is possible to achieve very large local refractive indicies that can slow down the speed of light to almost stopping, which could also give you enough time to switch things in an experiment.
  11. Mar 27, 2014 #10


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    Time in experiments tend to be relative in the sense that what matters is not the absolute time, but the time relative to the time is takes to perform an "operation".

    This is one reason you can investigate the same type of physics using so wildly different systems: some quantum systems have e.g. short coherence times but can be manipulalted very quickly (e.g. electronic systems) whereas other have very long coherence times but are difficult to manipulate at all. To some extent this is an intrinsic property: systems which behave quantum mechanically for long time (ins,atomes etc) do so because they are well insulated from the environment. which also makes them very difficult to manipulate quickly.

    Hence, your question really only makes sense if you specify HOW you you would like to perform the experiment.
  12. Mar 27, 2014 #11


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    It's a question, and I might have asked it myself if Khashishi had not beaten me to it. The more you can tell us about what problem you're trying to solve, and especially why the already known solutions are inapplicable for your problem, the more likely that we'll be able to give you a helpful answer.
  13. Mar 30, 2014 #12
    It would need to be infinitely smooth on a molecular level and have the perfect color. The problem with even having an almost infinitely small amount of light lost on each reflection is that the light is moving so fast and bouncing off every mirror millions of times every second which causes it to be absorbed quickly.
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