03-01-2013, 03:15 PM
LASER
1LASER.pdf (Size: 108.75 KB / Downloads: 64)
Properties of Laser:
Monochromatic: means it consists of one wavelength. Ordinary white light is a combination of
different wavelengths.
Directional:
Laser is emitted as a narrow beam in a specific direction. Laser beams can be
focussed to very tiny spots.
Coherent.
Spontaneous and Stimulated emission: According to Bohr's atomic model when an atom makes a
transition from upper energy state E2 to lower energy state E1 a radiation of frequency υ is emitted
where
E2 – E1 = hυ ; h is the Planck's constant.
Similarly an atom in the lower energy state E1 can absorb radiation of frequency υ and makes transition
to the higher energy state E2.
There are two possible types of emission:
Spontaneous emission is the process by which an atom in excited state undergoes a transition
to a lower energy at random. It has many applications as fluorescent tubes, cathode ray tubes,
light emitting diodes.
Stimulated emission is caused by an incident photon having energy equal to the difference of
energy between the two energy levels. The incident photon interacts with the atom of the upper
state and causes it to drop down to the lower state with the creation of a second photon. The
second photon has the same phase, frequency, polarization and direction of travel as the incident
photon.