Effect of small perturbations on the polarization of single-mode laser radiation with a homogeneous lasing transition line

T. V. Radina

We show that the dip in the intensity line shape of a single-mode laser can appear at definite experimental conditions in cases both of nonhomogeneously broadened line as well as homogeneously broadened line of the atomic transition. In both cases the dip is explained by the nonlinear character of the phenomenon. The saturation of the population difference of the involved atomic energy levels has its maximum in the vicinity of the line center. Therefore the saturation of the amplification is at maximum near the atomic line center, and, as a consequence, the lasing power is reduced.

Chun Wang, Jinsong Liu

I. S. Pashkevich, Iliya V. Doronin, E. S. Andrianov +1 more

The emission linewidth in active medium emerges due to homogeneous and inhomogeneous broadening. We demonstrate that in lasers with inhomogeneous broadening there is a critical pump rate, above which the special mode forms. This mode consists of locked-in oscillations of cavity mode and of the active atoms with different transition frequencies. Below the critical value of the pump rate, the radiation spectrum of the laser has a Gaussian profile, provided that inhomogeneous broadening is dominant. Above the critical value of pump rate, the special mode mostly determines the laser radiation spectrum. As a result, the spectrum attains Lorentz shape characteristic for homogeneous broadening. The formation of the special mode precedes lasing and that the critical pump rate plays the role of lasing prethreshold. We suggest a system where such a transition could be experimentally observed separately from lasing. We obtain expressions for the threshold and generation frequency of a single-mode laser where both homogeneous and inhomogeneous broadening are present.

Robert P. Lucht

Binoy Krishna Goswami, Dhruba J. Biswas

We have compared the impact of loss, pump, and frequency modulations on a single-mode homogeneously broadened laser under varying detunings and modulation frequencies. In the case of loss and gain modulations the impact on intensity shows a minimal behavior at the line center for gain values more than twice the lasing threshold. The system relaxation time with respect to any transient perturbation depends on the magnitude of detuning and is minimal at the line center. In the case of frequency modulation, the impact on intensity vanishes at the line center irrespective of the gain values. These results are based on linear analysis.

L. M. Khayutin