Dynamics of third-order nonlinearity of thiophene derivative by homodyne and heterodyne phase-tuned femtosecond optical Kerr gate

Using optically heterodyned detection combined with π/2 optical phase biasing in the optical Kerr gate (OKG) experiment we investigated complex third-order nonlinear optical susceptibility of solutions of bisbenzothiazole 3,4-didecyloxy thiopene (BBTDOT) in tetrahydrofuran (THF). With the use of ultrafast approx 100 fs laser pulses at 620 nm, the instantaneous, coherent part of the response is separated from an incoherent, time-delayed response. A power dependence analysis of the delayed part of the signal reveals that the signals originates in an effective χ nonlinear process due to population of a two-photon excited state. The magnitudes and the signs of the real and the imaginary components of the complex third-order optical susceptibility were determined independently by the heterodyned OKG and a concentration dependence homodyne Kerr gate measurement.