L7 - 3 and 4 level lasers

Question 1

Problem with level 3

Answer 1

Pump competes iwth pop of level 1
due to stim emission from lvel 3 into level 1 (thus decreasing pop inversion)

Question 2

Close to threshold what quantity in rate eqn is negligable

Answer 2

The stimulated terms
+- Sig Phi (N2-N1)

Question 3

To have pop inv in 3 level what is required

Answer 3

P > Gamma _21

Question 4

Level 4 laser rates

Answer 4

Gamma_10 > Gamma_21
This ensures pop invesion