Subject :- Applied Physics 2.

Topic :- Laser.

Difficulty :- Low.

Critical angle: When a ray passes from a denser medium to rarer medium. It bends away from the normal. As the angle of incidence increases, refracted ray bents more and more away from the normal. At a particular angle of incidence say i = $∅_c$ refracted ray glides the surface r = 90 degree .This angle is known as critical angle.

We know from Snell`s law sini / sin⁡r = $n_2$ / $n_1$

$sin⁡∅_c$ / sin ⁡90 = $n_2$ / $n_1$

$Sin ∅_ c$ = $n_2$ / $n_1$

Acceptance angle: The maximum angle of incidence for which the ray propagates down the fiber is called as acceptance angle.

$i_m$ = $Sin^{-1}$ NA