Unit 4

Quantum Physics

Einstein two-level energy diagram
Absorption transition
Spontaneous emission transition
Stimulated emission transition
Basic laser cavity
Ruby laser construction
Ruby three-level energy diagram
He-Ne laser construction
He-Ne energy-level scheme
Semiconductor laser p-n junction
Optical fibre construction
TIR inside optical fibre
Acceptance-angle geometry
Step-index refractive-index profile
Graded-index refractive-index profile
Single-mode propagation
Multimode propagation
Three-level laser
Four-level laser

$E = h ν = \frac{h c}{λ}$
$ν = \frac{c}{λ}$
$N = E_{t o t a l} \frac{λ}{h c}$
$\frac{N 2}{N 1} = e x p [- (E 2 - E 1) / (k T)]$
$E 2 - E 1 = - k T l n (\frac{N 2}{N 1})$
$sin C = \frac{n 2}{n 1}$
$N A = n 0 sin α 0$
$N A = n 1^{2} - n 2^{2} f or ai r$
$α 0 = sin^{- 1} (N A)$
$n 2 = n 1^{2} - sin^{2} α 0$
$I = \frac{P}{A} = \frac{4 P}{π d ^{2}}$