A nitrogen laser is a gas laser that produces an ultraviolet laser output with a wavelength of 337.1 nm. The gain medium or active medium in a nitrogen laser are nitrogen molecules in gaseous form. This pulsed laser produces multi-mode output i.e., it carries multiple rays and has high gain. It is used as a pumping source for dye lasers. A pumping source is an external source of energy that provides adequate energy to the gain medium to produce a population inversion state that is essential for lasing action.

Nitrogen laser operating mechanism 

Population inversion in nitrogen laser is achieved by an electrical pumping source. Normally, pumping is provided by direct electron impact where voltage is applied across the electrodes of the gas discharge tube which is filled with low-pressure nitrogen gas.

Consider the energy level diagram of a nitrogen laser. Here E₁ is the ground level and E₂ and E₃ are the excited energy levels. The molecules in the ground level get excited to the E₃ level when the voltage applied across the electrode causes a direct collision between electrons in the discharge tube. The upper laser lifetime in E₃ is 40 ns only, which requires quick pumping, which is possible via direct pumping from the N₂ ground state. On the other hand, the lifetime of the lower laser level i.e., E₂ of nitrogen laser is 10 µs which is quite a long duration. So, the laser self terminates after the electrons fall back to the ground state. That is why a nitrogen laser is known as a self-terminating laser. 

Typical nitrogen laser parameters

Applications of Nitrogen Laser
As mentioned earlier, nitrogen lasers are used for pumping tunable dye lasers, scientific research, spectroscopy and fluorescence studies, and fast-speed photography.