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A simple and inexpensive technique for stabilization of a CO2 laser used to optically pump a far infrared waveguide laser is discussed. The technique uses the fact that the output power of the CO2 laser varies as the output frequency is swept through the Doppler profile of the emission line. Stabilization is obtained by adjusting the mirror separation and forcing the output power to remain constant at the level corresponding to the desired pump frequency.

Type-B (axial) coherent bremsstrahlung spectra have been obtained with an energy resolution of 42 eV. These show a type of fine structure, due to the contributions of Umklapp events from different reciprocal-lattice vectors in the same reciprocal-lattice plane normal to the beam, not passing through the origin. A plane-wave theory fits the data well if atomic scattering factors for isolated atoms are used. The observation of crystal bonding (solid-state relaxation) effects on the coherent-bremsstrahlung intensities requires a more sophisticated theory for the treatment of the continuous background. Bloch-wave broadening effects are not seen at this resolution.