DAY 20 – DAW January

Lasers-Einstein A and B coefficients;Ruby and He-Ne lasers; Characteristics of laser light-spatial and temporal coherence; Focusing of laser beams; Three-level scheme for laser operation; Holography and simple applications.


Q 1. In He-Ne laser, what is the function of He gas? Explain the answer with the help of energy level diagram for He-Ne laser ? [15 marks]

Q 2. Explain the principle of (i) induced absorption, (ii) spontaneous emission and (iii) stimulated emission . Show that the ratio of Einstein’s coefficients is given by AB=8πhν3c3\frac AB=\frac {8\pi h \nu ^3}{c^3} [20 marks]

Video Solution at 11 pm