1. Home
  2. University physics volume 3
  3. Unit 2. modern physics
  4. Atomic structure
  5. Lasers

8.6 Lasers  (Page 2/9)

<< Chapter < Page
  University physics volume 3     Page 2 / 9
Chapter >> Page >
An illustration of the details of a compact disc. A laser beam hits the disc from below at right angles. The disc consists of three layers. The lower layer is a polycarbonate plastic layer with alternating pits and bumps. A thin layer of Aluminum is deposited on top of the plastic layer. A layer of laquer covers the disc, filling in the bumps and pits and forming a smooth upper surface. The entire disc, including all three layers, is 1.2 m m thick.
A compact disc is a plastic disc that uses bumps near its surface to encode digital information. The surface of the disc contains multiple layers, including a layer of aluminum and one of polycarbonate plastic.

A CD player uses a laser to read this digital information. Laser light is suited to this purpose, because coherent light can be focused onto an incredibly small spot and therefore distinguish between bumps and pits in the CD. After processing by player components (including a diffraction grating, polarizer, and collimator), laser light is focused by a lens onto the CD surface. Light that strikes a bump (“land”) is merely reflected, but light that strikes a “pit” destructively interferes, so no light returns (the details of this process are not important to this discussion). Reflected light is interpreted as a “1” and unreflected light is interpreted as a “0.” The resulting digital signal is converted into an analog signal, and the analog signal is fed into an amplifier that powers a device such as a pair of headphones. The laser system of a CD player is shown in [link] .

A photograph of the inner working of a CD player
A CD player and its laser component.

Blu-ray player

Like a CD player, a Blu-Ray player reads digital information (video or audio) stored on a disc, and a laser is used to record this information. The pits on a Blu-Ray disc are much smaller and more closely packed together than for a CD, so much more information can be stored. As a result, the resolving power of the laser must be greater. This is achieved using short wavelength ( λ = 405 nm ) blue laser light—hence, the name “Blu-” Ray. (CDs and DVDs use red laser light.) The different pit sizes and player-hardware configurations of a CD, DVD, and Blu-Ray player are shown in [link] . The pit sizes of a Blu-Ray disk are more than twice as small as the pits on a DVD or CD. Unlike a CD, a Blu-Ray disc store data on a polycarbonate layer, which places the data closer to the lens and avoids readability problems. A hard coating is used to protect the data since it is so close to the surface.

The different pit sizes and player-hardware configurations of a CD, DVD, and Blu-Ray player are illustrated. In each case, the pits are smaller than the size of the spot made by the laser beam on the surface of storage medium. On the left, the CD player, with 0.7 GB storage capacity, is shown. The CD laser has a wavelength of lambda equal to 780 nanometers, corresponding to a red color. It is focused by a lens, penetrating the CD material to a depth of 1.2 m m and forming a relatively large spot on the surface of the CD. In the middle, the DVD player, with 4.7 GB storage capacity, is shown. The DVD laser has a wavelength of lambda equal to 650 nanometers, corresponding to a reddish-orange color. It is focused by a lens, penetrating the DVD material to a depth of 0.6 m m and forming a smaller spot on the surface of the DVD than we saw on the CD. On the right, the Blue-Ray player, with 25 GB storage capacity, is shown. The blue-Ray laser has a wavelength of lambda equal to 405 nanometers, corresponding to a blue color. It is focused by a lens, penetrating the blue-ray disc material to a depth of 0.1 m m and forming a small spot on the surface of the disc.
Comparison of laser resolution in a CD, DVD, and Blu-Ray Player.

Summary

  • Laser light is coherent (monochromatic and “phase linked”) light.
  • Laser light is produced by population inversion and subsequent de-excitation of electrons in a material (solid, liquid, or gas).
  • CD and Blu-Ray players uses lasers to read digital information stored on discs.

Key equations

Orbital angular momentum L = l ( l + 1 ) ℏ
z -component of orbital angular momentum L z = m ℏ
Radial probability density function P ( r ) d r = | ψ n 00 | 2 4 π r 2 d r
Spin angular momentum S = s ( s + 1 ) ℏ
z -component of spin angular momentum S z = m s ℏ
Electron spin magnetic moment μ → s = ( e m e ) S →
Electron orbital magnetic dipole moment μ → = − ( e 2 m e ) L →
Potential energy associated with the magnetic
interaction between the orbital magnetic dipole
moment and an external magnetic field B → 		U ( θ ) = − μ z B = m μ B B
Maximum number of electrons in a subshell of
a hydrogen atom		 N = 4 l + 2
Selection rule for atomic transitions in a
hydrogen-like atom		 Δ l = ± 1
Moseley’s law for X-ray production ( Z − 1 ) = constant f

Conceptual questions

Distinguish between coherent and monochromatic light.

Got questions? Get instant answers now!

Questions & Answers

what is force
Afework Reply
The different examples for collision
Afework
What is polarization and there are type
Muhammed Reply
Polarization is the process of transforming unpolarized light into polarized light. types of polarization 1. linear polarization. 2. circular polarization. 3. elliptical polarization.
Eze
Describe what you would see when looking at a body whose temperature is increased from 1000 K to 1,000,000 K
Aishwarya Reply
how is tan ninety minus an angle equals to cot an angle?
Niicommey Reply
please I don't understand all about this things going on here
Jeremiah Reply
What is torque?
Matthew Reply
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment, moment of force, rotational force or turning effect, depending on the field of study.
Teka
Torque refers to the rotational force. i.e Torque = Force × radius.
Arun
Torque is the rotational equivalent of force . Specifically, it is a force exerted at a distance from an object's axis of rotation. In the same way that a force applied to an object will cause it to move linearly, a torque applied to an object will cause it to rotate around a pivot point.
Teka
Torque is the rotational equivalence of force . So, a net torque will cause an object to rotate with an angular acceleration. Because all rotational motions have an axis of rotation, a torque must be defined about a rotational axis. A torque is a force applied to a point on an object about the axis
Teka
When a missle is shot from one spaceship towards another, it leaves the first at 0.950c and approaches the other at 0.750c. what is the relative velocity of the two shipd
Marifel Reply
how to convert:m^3/s^2 all divided by kg to cm^3/s^2
Thibaza Reply
Is there any proof of existence of luminiferious aether ?
Zero Reply
mass conversion of 58.73kg =mg
Proactive Reply
is Space time fabric real
Godawari Reply
What's the relationship between the work function and the cut off frequency in the diagram above?
frankline Reply
due to the upthrust weight of the object varise with force in which the body fall into the water pendincular with the reflection of light with it
Gift
n=I/r
Gift
can someone explain what is going on here
falanga
so some pretty easy physics questions bring em
falanga
what is meant by fluctuated
Olasukanmi Reply
If n=cv then how v=cn? and if n=c/v then how v=cn?
Natanim
convert feet to metre
Mbah Reply
what is electrolysis
Mbah
Electrolysis is the chemical decomposition of electrolyte either in molten state or solution to conduct electricity
Ayomide
class ninekasindhtextbookurdusave
Ayesha Reply
can someone help explain why v2/c2 is =1/2 Using The Lorentz Transformation For Time Spacecraft S′ is on its way to Alpha Centauri when Spacecraft S passes it at relative speed c /2. The captain of S′ sends a radio signal that lasts 1.2 s according to that ship’s clock. Use the Lorentz transformati
Jennifer
<< Chapter < Page Page > Chapter >>
Practice Key Terms 6

Read also:

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, University physics volume 3. OpenStax CNX. Nov 04, 2016 Download for free at http://cnx.org/content/col12067/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'University physics volume 3' conversation and receive update notifications?

Ask