How Do Optical Drives Like CDs, DVDs, and Blu-ray Store and Retrieve Data?

[guppster]

Homework Statement

1. I have been recently wondering how is data stored on and retrieved from optical devices like CDs, DVDs, and Bluray. What makes these different storage types different from each other?

2. Why will a silver mirror not show a reflection when you sand the surface with very coarse sandpaper?

Homework Equations

The Attempt at a Solution

2. Is it because the coarse sandpaper will make small dents in the material, so the light will reflect off the surface in multiple directions, making it hard to see a clear image or is it because of another reason?

 

[cepheid]

For all of these optical drives, a laser is used to write data to the disks and then read it back from it. I think some well-placed Googling can get you pretty far on this question.

As for the other question, your answer is basically correct. Look up diffuse reflection vs. specular reflection. If the surface is perfectly smooth (compared to the wavelength of the light), then incoming rays that are all parallel will be reflected all parallel as well. So an image of the scene in front of the surface is faithfully reproduced. This is specular reflection. If the surface has all kinds of "canyons and valleys" in it, then the angle of incidence for different parallel rays is different, because they all strike different parts of the surface that are oriented differently. So, even if these rays are parallel initially, they won't be reflected parallel to each other, but instead in all different randomized directions. This is diffuse reflection, and it is the way that light is reflected from the vast majority of objects that you see on a day to day basis.

 

[Simon Bridge]

Duplicate of:
https://www.physicsforums.com/showthread.php?t=621886
... see other thread for replies.

 

[guppster]

Thank you cepheid and Simon Bridge!

 

[Nickie]

1. The storage capacity and retrieval process of optical devices such as CDs, DVDs, and Bluray are based on the principles of optical physics. These devices use a laser beam to read and write data on the surface of the disc, which is coated with a reflective material. The laser beam creates pits and lands on the surface, representing the data in binary code. The differences in storage capacity among these discs are due to the size and spacing of these pits and lands, which vary according to the technology used. CDs have a lower storage capacity compared to DVDs and Bluray due to their larger pit size and spacing. Additionally, Bluray uses a blue laser instead of a red laser, allowing for more precise and compact data storage.

2. The reason why a silver mirror will not show a reflection when sanded with coarse sandpaper is due to the scattering of light. When the surface of the mirror is sanded, it creates microscopic grooves and scratches, which cause the light to reflect in different directions instead of reflecting back in a single direction to form a clear image. This scattering of light is known as diffuse reflection, and it is the reason why the mirror appears dull and does not reflect a clear image.