Principle of Nd :

YAG laser It is a solid state laser. Nd represents Neodymium (Nd+3 ions are used). YAG represents Yittrium Aluminium Garnet (Y3 A15 O12). Some of the Y+3 ions are replaced by Nd+3. The crystal atoms of YAG do not take part into lasing action, but serve as a host lattice in which Nd+3 resides.

Construction

As shown in Fig, an elliptically cylinder reflector with both of its axis occupied by a flash lamp and Nd : YAG rod respectively. The light leaving one focus of the ellipse will certainly pass through the other focus after reflection from reflecting surface. Hence entire light generated by flash tube is focussed on the Nd : YAG rod. Optical resonator is formed by highly silvered reflecting surfaces as shown in Fig.

Working

In Fig, we have energy levels E1, E2 and E3 of Nd along with many other levels of YAG. E1 is ground state and E3 offers metastable state. Pumping takes place with light of wavelength 5000 A° to 8000 A° which excites Nd+3 ions to higher states. The metastable state E3 rapidly gets populated due to downward transitions from higher energy levels as none of them is metastable. Population inversion takes place between E3 and E2. A continuous laser of 10600 A° in infrared region is given out due to stimulate emission taking place between E3 and E2.

. Nd:YAG is one of the most popular type of solid state laser.Nd represents Neodymium ($Nd_{+3}$ ions are used).YAG represents Yittrium Aluminium Garnet ($Y_3$$A1_5$$O_{12}$). Some of the $Y_{+3}$ ions are replaced by $Nd_{+3}$. The crystal atoms of YAG do not take part into lasing action, but serve as a host lattice in which $Nd_{+3}$ resides. Construction: As shown in Fig.above, an elliptically cylinder reflector with both of its axis occupied by a flash lamp and Nd : YAG rod respectively. The light leaving one focus of the ellipse will certainly pass through the other focus after reflection from reflecting surface. Hence entire light generated by flash tube is focussed on the Nd : YAG rod.Optical resonator is formed by highly silvered reflecting surface as shown in the figure above. Energy level diagram: ![enter image description here][2] The energy levels $E_1$, $E_2$ and $E_3$ of Nd along with many other levels of YAG. $E_1$ is ground state and $E_3$ offers metastable state is shown in the figure above. Pumping takes place with light of wavelength 5000 A° to 8000 A° which excites $Nd_{+3}$ ions to higher states. The metastable state $E_3$ rapidly gets populated due to downward transitions from higher energy levels as none of them is metastable. Population inversion takes place between $E_3$ and $E_2$. A continuous laser of 10600 A° in infrared region is given out due to stimulate emission taking place between $E_3$ and $E_2$. As the laser is four level lasers, the population inversion cam be maintained throughout the laser action. Efficiency is also good. Function of ellipsoidal reflector: In between the consecutive flashes of the krypton lamp the Nd-YAG rod keeps on receiving light through multiple reflections on the ellipsoidal reflector.

Nd-YAG laser has applications is welding and drilling in hardware industry, surgery etc.