1. The problem statement, all variables and given/known data 2. Relevant equations γ=α+(1/2L)ln(1/Γ1Γ2) where gamma is gain, alpha is absorption constant, and Γ are reflection coefficients. 3. The attempt at a solution I'm a little stuck on how to start. If there was no semiconductor gain medium in the cavity then I could just use the equation to calculate it. But since there is one some of the photons are absorbed when they hit the medium. So I don't think I can use the gain equation I have, can I? I'm really not sure how to get started, tips would be appreciated.