Submillimeter-band solid state distributed feedback laser

The threshold characteristics of a solid state laser with anisotropic gain is analyzed. Allowance for anisotropy of the gain results in an asymmetric mode spectrum and a complex coupling coefficient that depends upon the thickness of the specimen, the permittivity of the active and passive media and the frequency of the acoustic wave. Resonant Bragg diffraction scattering is examined, assuming that the active medium, which is created by a magnetic field and an ultrasonic wave, is contained in a homogeneous dielectric medium with permittivity Epsilon sub 1. An acoustic wave with wave number Beta sub zero = 2 PI/Lambda propagating along the x axis caused the permittivity to change, thus facilitating distributed feedback. It is found, in contrast to the simple isotropic case, that the coefficient of absorption and the coupling coefficient change significantly: an effective index of refraction of the wave and an effective complex coupling coefficient occur which depend upon the thickness of the active region and the permittivities of the active and passive media. The threshold electron concentration is analyzed as a function of the feedback coefficient, of temperature for the first four modes and of the specimen length.