Phonon screening in high-temperature superconductors.

In good conductors optical phonons are usually screened, and therefore not observed. However, sharp features due to infrared-active modes in the copper-oxygen planes are observed in the optical conductivity of Pr1.85Ce0.

Reflectivity measurements on hot reactive liquids using a FIR laser.

The experimental procedures and precautions required to measure liquid-alloy reflectivities with a cw far infrared (FIR) laser are described. The output of a carefully stabilized optically pumped FIR laser was channeled to a melted sample contained in a silica holder under a He atmosphere. By maintaining specular reflection and alloy homogeneity, reflectivities reproducible to +/-7% were routinely obtained.