Time resolved Raman induced phase conjugation in polymers and semiconductors

Abstract

Time resolved Raman induced phase conjugation (TRIPC) and degenerate four wave mixing were used to investigate the magnitude and time response of the third order nonlinearity as well as vibrational and photon relaxation times in different liquids and solids. A phase conjugation geometry was used in these experiments with two counter propagating picosecond pump beams and a picosecond probe beam interacting in a nonlinear medium and generating a phase conjugate signal beam. For the vibrational and phonon relaxation time measurements one of the picosecond counter propagating beams was a broadband super continuum extending throughout the visible spectrum. By delaying one of the interacting pump beams relative to the other pump and probe beams we were able to determine, with picosecond resolution, the intensities of both the degenerate and Stokes shifted phase conjugate signals as a function of time. We have applied these techniques to determine the magnitude of the third order nonlinearity of several polymer and semiconductor samples and to measure the temporal behavior of the nonlinear interactions with picosecond resolution. TRIPC has been used for obtaining fundamental information about resonant vibrational interactions. In particular TRIPC spectra in CS2, nitrobenzene, and calcite, spanning 3000 cm−1 have been obtained. By delaying one of the pump beams and monitoring the intensity of a desired Stokes frequency component, information about the vibrational dephasing time was obtained. Performing the time resolved experiment in CS2 and calcite, a vibrational dephasing time of 24 ps for the 656 cm−1 vibration in CS2, and 8 ps for the 1086 cm−1 vibration in calcite were measured. The lifetimes are in good agreement with the work of Fisher and Lauberau (Chem Phys. Lett. 35, 6(1975)) (22 ps for CS2) and Alfano and Shapiro (Phys. Rev. Lett. 26, 1247 (1971)) (8.5 ps for calcite ) using conventional picosecond time resolved excite and probe Raman techniques. These experimental results and measurements in several other samples will be discussed.