Numerical Study of the Dynamics of Laser Lineshape and Linewidth

Abstract

A rate equations model for lasers with homogeneously broadened gain is written and solved in both time and frequency domains. The model is applied to study the dynamics of laser lineshape and linewidth using the example of He-Ne laser oscillating at λ = 632.8 nm. Saturation of the frequency spectrum is found to take much longer time compared to the saturation time of the overall power. The saturated lineshape proves to be Lorentzian, whereas the unsaturated line profile is found to have a Gaussian peak and a Lorentzian tail. Above threshold, our numerical results for the linewidth are in good agreement with the Schawlow-Townes formula. Below threshold, however, the linewidth is found to have an upper limit defined by the spectral width of the pure cavity. Our model provides a unique and powerful tool for studying the dynamics of the frequency spectrum for different kinds of laser systems, and is also applicable for investigating lineshape and linewidth of pulsed lasers.