1. For instance: data reported by F. Julien and J. M. Lourtioz during the discussion of their talk ?Power performances on efficient cw FIR laser lines with uniform transmisson couplers?, V. Int. Conf. on Infrared and Millimeter Waves, Oct. 6?10, 1980, Wuerzburg.
2. M. Tacke, IEEE J. Quantum Electron.,QE-18, 2022 (1982).
3. E. A. J. Marcatili, R. A. Schmeltzer, B. S. T. J.43, 1783 (1964).
4. J. Heppner, C. O. Weiss, U. Huebner, G. Schinn, IEEE J. Quantum Electron.,QE-16, 392 (1980).
5. R. L. Abrams, IEEE J. Quantum Electron.,QE-8, 838 (1972).