A 250-μm-long InGaAsP laser has an internal loss of 40 cm-1. It operates at 1.55 μm in a single mode, with the modal index 3.3 and the group index 3.4. Calculate the photon lifetime. What is the threshold value of the electron popu- lation? Assume that the gain varies as G = G₁ (N – No) with G₁ = 6 × 10³ s−¹ and No = 1 × 108.