NONLINEAR SPECTROSCOPY OF NARROW-GAP PR-B A-CU-O SEMICONDUCTOR-FILMS WITH THE AID OF BIHARMONIC PUMP

The dependences of the efficiency eta of self-diffraction of picosecon d pulses on their frequency offset OMEGA were determined for Pr-Ba-Cu- O semiconductor films. These dependences were similar to those already reported (for Ni and Y-Ba-Cu-O in the resistive phase) and had a cent ral peak (eta approximately 10(-7) for Absolute value of OMEGA less-th an-or-equal-to 10 cm-1) and wide wings (eta approximately 10(-9) for A bsolute value of OMEGA greater-than-or-equal-to 10 cm-1) with a jagged profile because of phonon resonances. An analysis was made of the cau ses of this similarity, of the asymmetry of eta (OMEGA) relative to th e sign of OMEGA, and of temperature singularities. Although the positi on of a combination electron resonance (interband transition edge) of Pr-Ba-Cu-O was within the range of variation of OMEGA, its identificat ion was complicated by the presence of nearby (on the scale of OMEGA) phonon modes.