Question

The condition for achieving laser action are
(i) The system must be in a state of population inversion
(ii) The excited state of the system should be in metastable state
(iii) The atom should be in lower energy state
(iv) No conditions required

Answer 1

Hint: Light from the laser beam is electromagnetic in nature as a light from an ordinary source but a laser beam has characteristic high directionality, high intensity, extraordinary monochromaticity, and high intensity.

Complete Step-by-Step solution:
Laser is an abbreviation of light amplification by stimulated emission of radiation as symbol equally suggested that the process of stimulated emission of radiation is used to amplify light.
The population inversion occurs only in between the metastable state and lower state.
Under normal conditions of thermal equilibrium the number of atoms in higher energy state is considered a smaller than the number of atoms in lower energy state. Hence non equilibrium condition is created artificially in which higher energy States should be more populated than the lower energy state this is known as population inversion. A system in which population inversion is achieved is called an active stimulus.
Let N1 be the number of atoms in the lower energy state E1 and N2 be the number of atoms in the higher energy state E2.
Under normal condition of thermal equilibrium lower energy state contain more active than in the higher energy state that is normally i.e. N1>N2

For laser action the higher energy state should be more populated and the lower energy state N2>N1. So to convert the normal condition of the population, energy is supplied to lower energy states. This applied energy excites the atom from lower energy state to higher energy state. That higher energy state is thus more populated and a lower energy state is the depopulated. The condition of population in the version can be achieved by pumping.
The lifetime of an atom in an excited state is a very short duration of order, however some of the excited states have a lifetime greater than that of the. Such a relatively long lived excited state is called a metastable state. Metastable can be defined as a state where excited atoms can remain for a longer time than normal states. The medium that has a metastable state is called the active medium.
Correct options are (i) (ii) (iii)

Note: There are three main parts of any laser first active medium second pumping system third resonator cavity or optical cavity the active medium supports the metastable state of longer duration of the order of 10 power minus 3 second which helps in maintaining condition of population inversion it provides Energy in correct in amount to exercise the atom from ground state to excited state is known as pumping.