WAVE-DISPERSED 3RD-ORDER NONLINEAR-OPTICAL PROPERTIES OF C-60 THIN-FILMS

Results of wave-dispersed third harmonic generation measurements in su blimed C-60 thin films are reported and discussed within a three-level model. Two strong resonant enhancements in cubic susceptibility X((3) ) (-3 omega; omega, omega, omega) are observed. The first one, occurri ng at a fundamental wavelength of 1.3 mu m with a X((3))(-3 omega; ome ga, omega, omega) maximum value of 6.1X10(-11) esu, is interpreted in terms of a two-photon resonance with the one-photon forbidden electron ic T-1g level. The second resonance at 1.064 mu m, with a maximum valu e of X((3)) (-3 omega; omega, omega, omega)=8.2X10(-11) esu is interpr eted as a three-photon resonance with the lowest one-photon allowed T- 1u electronic level.