Role of Petermann´s K-factor in semiconductor laser oscillators-a further note

The classical Schawlow-Townes formula for the linewidth of a laser should be multiplied by a factor K´ = (1+α_A²)K/2. In this formula, α_A, is the ratio of changes in the real and imaginary parts of the compl resonant frequency resulting from a change in carrier density, and K is Petermann´s factor. It is shown here that this factor is identical to a result reported in 1971 by other authors in connection with impact oscillators.