The active medium

the material used as the active medium determines

LASER wavelength

preferred pumping methode

order of magnitude of the laser output

the efficiency of the laser system

We saw that the tow basic requirements for laser action are

population Inversion between the upper and lower laser energy levels

Tte active medium must be transparent to the output wavelenght

The active medium determines most of the laser properties, and that is why the laser name is derived from the name of the active medium

Lasers can be divided into groups according to diffirent criteria

the state of matter of the active medium : solid, liquid, gas, or plasma

the spectral range of the laser wavelength : visible spectrum , Infra-Red (IR) spectrum , etc

the excitation (pumping) method of the active medium : optical pumping , electric pumping , etc

the characteristics of the radiation emitted from the laser

the number of energy levels which participate in the lasing process

Monochromaticity

Monochromaticity means "One color" . To understand this term , examine "white light" which is the color interpreted in the mind when we see all colors together . When "white light" is transmitted through a prism , it is divided into the different colors which are in it , as seen in figures

Examples for electromagnetic waves

Radio- waves which have wavelength of the order of meters , so they need big antennas (the dimension of an antenna are of the same order of magnitude as the wave)

Microwaves which have wavelength of the order of centimeters . As an example : in a microwave oven , thes wavelengths can not be transmitted through the protecting metal grid in the door , while the visible spectrum which hav much shorter wavelength allow us to see what is cooking inside the microwave oven through the protecting grid

X- Rays which are used in medicine for taking pictures of the bone structure inside the body

Gamma Rays which are so energetic , that they cause ionization , and are classified as ionizing radiation

Electromagnetice Radiation

the electromagnetic radiation out of the laser can be in any part of the spectrum ,including the ,visible spectrum,the Ultra-violet(UV) spectrum,the Infra-Red(IR) spetrum and beyond.

Laser Radiation and its properties

laser technology is of the most rapidly developing areas in modern technology.When the laser was invented ,in 1960,it was classified as a solution in search of a problem ,and today laser technology is applied in many different areas such as :medicine,communication,daily use,military,and industry .To explain how the laser can be applied in such diverse areas, we need to understand the basic physical principles of the operathion of a laser

In principle, the laser is a device which transforms energy from other forms into electromagnetic radiation this is a very general definition , but it helps to understand the basic physics of the laser . the energy put into the laser can be in any form such as electromagnetic radiation, electrical energy, chemical energy , etc . Energy is always emitted from the laser as electromagnetic radiation (which includes light beams).

From this light output , the laser got part of its name :LASER= Light Amplification by Stimulated Emission of Radiation . As we see, the word laser started as acronym but it is now accepted as a word , with other words derived from it : "to lase " ,"lasing" etc . We will try to obtain a qualitative picture of quantum nature of laser , based on some basic principles which came from the advanced mathematical tools . Before studying about lasers , you must be familiar with basic terms use to describe electromagnetic waves :

Wavelength ,Frequency , Period , Velocity of light and Index of refraction