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I Blu ray discs

  1. Jul 21, 2016 #1
    blu ray disc has a shorter wavelength than a red laser (650nm), but how does having shorter wavelength effect storage space? answer in laypersons terms.
  2. jcsd
  3. Jul 21, 2016 #2


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    If you imagine the laser beam as a thin cylinder that has a small radius r , then this radius r depends on the wavelength of the laser. The smaller the wavelength the smaller the radius r. And the smaller the radius r is, the smaller is the spot that the beam leaves on the disc when we do recording of data (the laser beam switches between on to record a 1 bit and off to record a 0 bit, actually it is high power/intensity for the 1bit and low power for the 0 bit). The smaller that spot is, this means that the smaller one bit of data is, so we can put more bits on the same disc, so more data.
  4. Jul 21, 2016 #3
    So you mean that inside the CD player, there is a miniature laser beam? but if there is a laser beam inside the cd player then is this laser red or blue and how does blu ray have blue laser? So is the laser inside the disc? or is it in the cd player?
    Last edited: Jul 21, 2016
  5. Jul 21, 2016 #4
    So can we use this analogy?

    If you've ever had to squeeze a certain amount of text on a single sheet of paper (maybe to make a poster) and found it difficult to get everything on, you'll know there's a simple solution: you just make your words a bit smaller (lower the font size). The same idea works when you're writing computer data on discs with laser beams. You can store more on a DVD than a CD by using a laser beam that "writes smaller". And to read or write a Blu-ray disc, you use a laser to write even smaller still.
  6. Jul 21, 2016 #5
    I think i know somewhat what happens but correct me if i m wrong. the cd drive shins a laser that is red in color and the blu ray disc reflects a blue laser beam. So originally the cd player shines a red beam of laser but blue beam is reflected from the blu ray disc
  7. Jul 21, 2016 #6


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    The cd player/recorder has electronics and focus lens that produce and focus a red laser beam . The Blue-Ray player/recorder has electronics and lens that produce and focus a blue laser beam. The beam is produced by the player/recorder and when we choose to play the disc, the beam is produced with low power and is reflected by the surface of the disc. When we choose to record the disc, the beam is produced with high power and can "burn" the surface of the disc at tiny spots whose radius depend on the wavelength of the beam, the radius of the spot is smaller for blue beams and larger for red beams.

    yes that is exactly the analogy.
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