A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.
Laser = Acronym for Light Amplification By Stimulated Emission of Radiation
Characteristics of laser
1. It is monochromatic ie. having single color.
2. It is collimated i:e Unidirectional.
3. It is coherent i:e same phase.
4. It has high intensity.
The different terms associated to laser are as follows :
1. Stimulated Absorption
When suitable wavelength of light falls on atoms at ground state, then it absorbs energy form the
light. after absorbing energy the atoms get excited to higher or excited state. This process is called
2. Spontaneous Emission
The process of emission of radiation when atom falls from excited to lower or ground state without the influence of any external means is called spontaneous emission.
3. Stimulated Emission
The process of emission of radiation when atom falls from excited to lower or ground state with the influence of any external means is called stimulate emission.
4. Meta Stable State
Generally atoms cannot stay for a longer time at excited state. it can fall to the ground state after 10^-8 seconds. Somehow if atoms stay at excited state for longer time i:e 10^-3 second , then it is called meta stable state.
Hence, the state at which atoms can stay at excited state for 10^-3 second is called meta stable state. It is very important for lasing action.
5. Population Inversion
Generally, no. of atoms at lower state is more than that of excite state. Increasing the no. of atoms at excited state in such away that no. of atoms at this state is more than that of ground state. Hence, achieving more atoms at excited state than at ground state is called population inversion. This is obtained using optical pumping.
6. Optical Pumping
The process due to which population inversion takes place is called optical pumping. It is very important for lasing action.