STUDY OF THE FAR-INFRARED AND MM-WAVE CONDUCTIVITY OF YBCO IN THE NORMAL-STATE

An accurate determination of the optical conductivity sigma(nu) of hig h-T-c materials at low frequencies (nu < 100 cm(-1)) is still an open problem. In the present paper we report new far-infrared data showing that the LaAlO3 crystal, on which high-quality YBCO films can be depos ited, is well transparent at low frequencies. Test measurements have a lso been performed by employing the ENEA compact FEL facility; prelimi nary results indicate the possibility to obtain high-accuracy spectros copic data in the mm-wave region. On the basis of these results, we ha ve in program mm-wave and far-infrared transmittance measurements on t hin YBCO films on LaAlO3, in order to get new information on the low-f requency behaviour of sigma(nu).