Suitable Lasers Research Articles

Nonlinear Landau absorption in III-V semiconductors near the fundamental absorption edge.

Analytical investigations have been made of nonlinear Landau absorption in important III-V semiconductors such as GaAs, GaSb, InSb, and InAs which have been irradiated by suitable lasers of photon energies (\ensuremath{\Elzxh}\ensuremath{\omega}) nearly equal to the band-gap energies (\ensuremath{\Elzxh}${\ensuremath{\omega}}_{g}$) in the presence of a large magnetostatic field. A coherent radiation-exciton interaction model has been used for the direct allowed transitions between the n=0 Landau subbands. The result obtainable for linear magnetoabsorption using the present model agrees very well with that obtained in the 1960's using a completely different approach. The effective nonlinear Landau absorption ${\ensuremath{\alpha}}^{\mathrm{nonlin}({B}_{0})}$ has been studied by examination of the imaginary part of the third-order optical susceptibility. The contributions from the higher-order susceptibilities have been neglected. The Wannier-Mott exciton wave function \ensuremath{\psi}(0) is found to play a very important role in the nonlinear Landau absorption processes as it occurs in the fourth power in the expression for ${\ensuremath{\alpha}}^{\mathrm{nonlin}({B}_{0})}$. For near-band-gap resonant excitation in the true continuum with \ensuremath{\Elzxh}(\ensuremath{\omega}-${\ensuremath{\omega}}_{g}$) less than the crystal exciton rydberg, \ensuremath{\Vert}\ensuremath{\psi}${(0)}^{2}$\ensuremath{\Vert}\ensuremath{\gg}1 and its contribution must be recognized under this regime. The renormalization of the crystal band gap due to the exciton rydberg and the light shift has also been discussed.

Nonlinear Absorption in III—V Semiconductors

AbstractA coherent radiation‐exciton interaction model is employed to study analytically the phenomenon of nonlinear absorption in important III—V semiconductors (viz., GaAs, GaSb, InSb, InAs), the crystals being irradiated by suitable lasers with energies (hω) nearly equal to the band gap energies (hωg). The nonoptical processesare accounted for phenomenologically by introducing a damping parameter into the equation of motion of the probability amplitude of the excited electron—hole pair state. The Wannier‐Mott type of exciton wave function is found to be responsible for the giant nonlinearity of the crystal absorption coefficient in the near resonant optical interband transition regime with h | ω ‐ ωg | of the order of the crystal exciton binding energy. The effect of renormalization of the crystal band gap in the presence of Coulomb interaction and Starkbroadening is also discussed.

Thermonuclear fusion by high-power lasers

It may be possible to ignite small deuterium-tritium pellets by the focused radiation of powerful lasers. Crucial for the success of this alternate approach to fusion energy is the understanding of the interaction of intense laser radiation with plasma and the construction of suitable lasers with powers in the 100 TW regime. The author describes the present status of this field with particular emphasis on the interaction problem and its implication on the wavelength of the laser, existing high-power laser installations and trends in future laser development.

Long-path monitoring of atmospheric pollutant gases

Limitations of present laser techniques (1) Availability of suitable lasers. Most important factors are (a) tunability over the atmospheric window regions, (b) stability and (c) long-term operating characteristics. (2) Atmospheric turbulence, which limits detection sensitivity. (3) Interferences, which limit selectivity. (4) Portability and costs, which severely limit utilization.