Q1.What Is a Laser ?
Answer:
The term "laser" stands for "light amplification by stimulated emission of radiation."
It usually denotes a device for this purpose or the light beam produced by it.
<The basic structure of a laser system is shown below.>
The laser system generally consists of
(a) an active medium that can amplify light
(b) reflectors to return light.
The light is amplified in the active medium while it reciprocates between two reflectors.
Laser beams are part of this amplified light extracted from the reflectors.
Q2.How Does Laser Light Compare with Other Light ?
Answer:
(a) Light from an incandescent lamp (incoherent radiation)
(1) No directionality
(2) A mixture of various wavelengths
(3) Incoherent phases (temporal relations)
(4) Light waves do not prevail long
<Light from electric lamp>
(b) Features of laser light
(1) High directionality
(2) Single wavelength
(3) Coherent phases
(4) Light waves prevail long
<Laser light (coherent radiation)>
Q3.Are There Various kinds of Lasers ?
Answer:
There are soild-state, gas, liquid, and semiconductor lasers.
Their typical example and applications are listed below.
Type of laser |
Typical example |
Wavelength (nm) |
Applications |
Solid-state laser |
Ruby laser |
694 |
Machining |
YAG laser |
1060 |
Laser knives |
Liquid laser |
Dye laser |
320~1200 |
Measurement |
Gas laser |
He-Ne laser |
632 |
Measurement, printers, optical disks |
Argon ion laser |
488,515 and others |
Printers, machining, medical |
CO2 gas laser |
1060 |
Machining, laser knives |
Semiconductor laser (laser diode) |
GaAlAs laser |
750~880 |
Printers, optical disks |
InGaAsP laser |
1300,1500 |
Optical communication |
InGaAIP laser |
670 |
Measurement, printers,
bar-code readers |
Q4.How Do Semiconductors Emit Light ?
Answer:
Electrons in atoms or molecules have different values of energy that are not continuous.
To raise an electron at a low energy level to a higher level, some energy must be given to it by light or an electric current.
An electron at a high energy level is unstable and tends to transit to a lower energy level.
When it does, it emits light of a wavelength proportional to the energy level difference.
This light emission occurs in two ways: spontaneous emission and stimulated emission.
In (a) above, electron at the E2 level transit to the E1 level independently of each other, thus without coherent temporal relations (phase) among them when they emit light.
In (b) on the other hand, under influence of the incident light, light is emitted with the same wavelength and the same phases as those of the incident light.
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