Astronomy
In astronomy, most earth based
telescopes run into a problem when
trying to look at very fine points in the sky. The earth's atmosphere
is very turbulent, and higher power telescopes have problems with
clarity and are very blurry. A method called "adaptive optics" allows
observers to correct turbulence from the atmosphere as the image is
being seen by using a series of moveable mirrors to deform the image in
the exact opposite way the atmospheric turbulence
did.
A diagram of adaptive optics (Left), and a laser demonstrating a laser guide star (right).
Image Credit (left): http://www.brighthub.com/science/space/articles/22545.aspx?image=48391
Image Credt (right): http://www.gemini.edu/gallery/v/gn/lgs/lgs_from_cfht_green_sm.jpg.html
Adaptive optics work well to solve the problem of turbulence, but it requires the use of a guide star, which for a time was just a bright star in the sky. Later, a laser was used to create and artificial guide star. Here's how the Keck Observatory in Kamuela, Hawaii uses a laser in a very special way:
"In
the upper part of the Earth's mesosphere, [between 80 and 100
kilometers], there is
a ... thick layer rich in [sodium] atoms, deposited by the ablation of
micrometeorites. These atoms can be excited and caused to radiate by
sponateous emission by projecting a 10-14 Watt pulsed laser tuned [such
that the sodium atom will resonate] in the direction of the science
target. The magnitude of this artificial guide star ... varies with
laser power, beam collimation, and [sodium]
column density." A diagram of adaptive optics (Left), and a laser demonstrating a laser guide star (right).
Image Credit (left): http://www.brighthub.com/science/space/articles/22545.aspx?image=48391
Image Credt (right): http://www.gemini.edu/gallery/v/gn/lgs/lgs_from_cfht_green_sm.jpg.html
Adaptive optics work well to solve the problem of turbulence, but it requires the use of a guide star, which for a time was just a bright star in the sky. Later, a laser was used to create and artificial guide star. Here's how the Keck Observatory in Kamuela, Hawaii uses a laser in a very special way:
(credit: http://www2.keck.hawaii.edu/optics/lgsao/lgsbasics.html)
(paraphrasing for clarity and to bring the quote to a level of understanding equal to the rest of the project)
Using the laser to excite the sodium atoms in the earth's atmosphere gives the telescope a "star" that it can follow. This artificial star moves around just like the regular turbulence of the atmosphere, allowing for more accurate corrections with adaptive optics.
CD's
and
DvD's
For
the last decade or so, discs have been the majority of physical
information storage,
where CDs, DVDs, and Blu-rays are some of the most mobile. The physical
properties of disks begins at the microscopic level. Digital
information is
stored and read in combinations of 1s and 0s, which appears in the form
of
hills and valleys of a very thin aluminum
layer on the disk itself. A
laser is directed at the disk, where the
light from the laser passes through a protective but non-reflective
polycarbonate layer, hits the aluminum layer, and then bounces back.
The "hills" and "valleys" of a CD and a DVD
Image credit: http://materion.com/Businesses/Microelectronics%20and%20Services.aspx
Each hill or
valley is distinguished as a 1 or a 0, and to do this the laser is
pointed as
a very small angle. An optical pickup is placed next to the laser, so
that when
the laser hits a "hill", it reflects into the pickup. When the laser
hits valley, however, the laser reflects at a different angle, and does
not hit
the pickup. These
combinations of hitting and missing translate into 1s and 0s. Each time
the optical pickup receives a signal from the laser, it's translated
into a 1, and each miss is translated as a 0. An entire disk acts as a
single track starting
from the center, like a vinyl record. The laser and optical pickup are
placed on a track that moves
back and forth along one side of the disk, while the disk itself spins,
allowing the laser to read the massive spiral of information.
This poses a problem as the track gets further along the disk; the length of a single revolution on the outer part of the disk is much larger than the center. In order to account for this, the disk itself will speed up or slow down depending on where the laser is reading. (Fun note: now you know that if the disk is spinning faster in your computer, the laser is reading the inner part of the disk!)
Using aluminum layers provides a small problem; the amount of information that can be placed on the disk is very limited. In order to help solve this problem, the dual-layer disk was developed. In essence, a dual-layer disk is a disk with a second readable layer between the aluminum plate and the clear polycarbonate layer. This layer is actually made of ink, and when it is hit by a high power and very focused laser, it will replicate the optical properties of an aluminum layer. This solves the single layer problem, but is fairly hard to perfect.
For
the last decade or so, discs have been the majority of physical
information storage,
where CDs, DVDs, and Blu-rays are some of the most mobile. The physical
properties of disks begins at the microscopic level. Digital
information is
stored and read in combinations of 1s and 0s, which appears in the form
of
hills and valleys of a very thin aluminum
layer on the disk itself. A
laser is directed at the disk, where the
light from the laser passes through a protective but non-reflective
polycarbonate layer, hits the aluminum layer, and then bounces back. Image credit: http://materion.com/Businesses/Microelectronics%20and%20Services.aspx
Each hill or
valley is distinguished as a 1 or a 0, and to do this the laser is
pointed as
a very small angle. An optical pickup is placed next to the laser, so
that when
the laser hits a "hill", it reflects into the pickup. When the laser
hits valley, however, the laser reflects at a different angle, and does
not hit
the pickup. These
combinations of hitting and missing translate into 1s and 0s. Each time
the optical pickup receives a signal from the laser, it's translated
into a 1, and each miss is translated as a 0. An entire disk acts as a
single track starting
from the center, like a vinyl record. The laser and optical pickup are
placed on a track that moves
back and forth along one side of the disk, while the disk itself spins,
allowing the laser to read the massive spiral of information. A breakdown of a CD
Image Credit: http://www.howstuffworks.com/cd.htm/printable
Image Credit: http://www.howstuffworks.com/cd.htm/printable
This poses a problem as the track gets further along the disk; the length of a single revolution on the outer part of the disk is much larger than the center. In order to account for this, the disk itself will speed up or slow down depending on where the laser is reading. (Fun note: now you know that if the disk is spinning faster in your computer, the laser is reading the inner part of the disk!)
Using aluminum layers provides a small problem; the amount of information that can be placed on the disk is very limited. In order to help solve this problem, the dual-layer disk was developed. In essence, a dual-layer disk is a disk with a second readable layer between the aluminum plate and the clear polycarbonate layer. This layer is actually made of ink, and when it is hit by a high power and very focused laser, it will replicate the optical properties of an aluminum layer. This solves the single layer problem, but is fairly hard to perfect.