Names:______________________________________

1
Names______________________________________
PH103, Resolution April 7
1. On the right is a scanning tunneling
microscope (STM) image of the bit structure on a
CD. As the laser scans across the spinning disk,
the pock marks reflect laser light differently
then the flat areas. Light from the flat areas
end up being detected to give a binary 1 and
those from the pock marks dont make it into the
detector giving a binary 0. To resolve the
individual bits, the system needs to be able to
resolve two points a distance of 1 micron (1.0 x
10-6 m) apart. This is the smallest distance
between a pock mark and a flat area. The laser
commonly used is a 780 nm (780 x 10-9m)
semiconductor diode laser. If the lens diameter
is just 3 mm, what focal length is required of
the lens?
www.nanomotor.de
2. Blue-ray uses a laser with a wavelength of 405
nm. How much better resolution can you get with
Blue Ray? How much more information can you store
on a disk?
Resolution twice as good since s is twice as
small You could fit twice as many pock marks and
be able to read them, so you could have twice as
much data