Question

Explain construction and working of Nd: YAG laser. 

Answer 1

1. It is solid state laser
2. Nd represents Neodymium
3. YAG represents yittrium Aluminium Garnet 

1. As shown in figure, 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 focus after reflection from reflecting surface. Hence after light generated by flash tube is focussed on the
Nd: YAG rod.
2. Optical resonator is formed by highly silvered reflecting surface.

Working: 

1. We have energy level E₁, E₂ and E₃ of Nd along with many other levels of YAG. E₁ is ground state and E₃ offers metastable state. 
2. Pumping takes place with light of wavelength 5000A⁰ to 8000A⁰ which excites ND ions to higher state. The  metastable state E3 rapidly gets populated due to downward transitions from higher energy level as none of them is stable.
3. Population inversion takes place between E₃ and E₂. A  continuous laser of 10600A⁰ in infrared region is given out due to simulate emission taking place between E₃ and E₂.