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.
The collisional-radiative equilibrium model has been developed in order to investigate the population inversion on aluminum plasma. The population inversion has been established between lower 3s (^{3}P^{0}_{1},^{1}P^{0}_{1}) and upper 3p (^{3}P_{0},^{1}S_{0}) levels. The vacuum ultra-violet lasing on neon-like aluminum ions provides wavelengths of 111.9 nm, 143.2 nm, 157.3 nm. The rate of relative density population, between lower 3s ^{1}P^{0}_{1} and upper 3p ^{3}P_{0} levels, reaches its highest value of 7.16 at the electron density of 10^{19} cm^{-3}. The modified expression of optical escape factor, in the case of Doppler profile, was introduced in the calculation of opacity effect on the gain magnitudes. The resonance radiation trapping by 3d configuration alters drastically the gain values. A gain greater than 1 cm^{-1} was found between lasing levels 3s ^{3}P^{0}_{1} and 3p ^{3}P_{0}. The enhancement of gain was due to the pumping of the upper level by dielectronic recombination process from the ground state of fluorine-like and by the inner-shell ionization process from excited levels of sodium-like ions.
Laser rate equations are written and solved in the frequency domain for homogeneous as well as for inhomogeneous gain. The resulting laser model is capable of describing the fine structure as well as the dynamics of the laser frequency spectrum. The calculation shows that laser lines have a Lorentzian-like lineshape. The linewidth is found to be close to the spectral width of the cavity in case of inhomogeneous gain, whereas it is proved to approach the quantum limit for homogeneous gain.
A novel method based on two-pulse excitation of a hollow cathode discharge to determine metal atoms diffusion coefficients in noble gases was tested in Cu-He and Cu-Ne systems. The excitation conditions such as time duration of the discharge current pulses and configurations of the hollow cathode discharge were checked. Measurements carried out over the wide range gas pressures allowed obtaining the Cu atoms time-decay curves from which the diffusion coefficients were calculated. The values for Cu atom diffusion coefficients of 570 and 310 cm^2 s^{-1} mbar in He and Ne, respectively were in a good agreement with earlier reported data achieved by using the absorption spectroscopy method. The diffusion coefficient of Cu in ^3He, the lighter isotope of helium, was also found to be 670 cm^2 s^{-1} mbar that agreed well with the kinetic theory of gases. To authors believe this value was not reported previously.
The results of experimental investigations of diffuse (volume) nanosecond elevated-pressure discharges in a non-uniform electric field at a time resolution of a recording system being equal to ≈100 ps are presented in this paper. The application of the runaway electrons preionized diffuse discharge is promising for obtaining high-power radiation pulses in the VUV and UV spectral region.
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