document: We use open and close aperture Z-scan experiments, in analogy to the saturation absorption work discussed earlier in water [8], to respectively measure the β and n2 for a series of primary alcohols with the help of 1560nm femtosecond laser pulses, however, with the important inclusion of an optical-chopper. The vibrational combination states of the alcohols are coupled by the femtosecond laser pulses at 1560nm. These couplings result in the absorption of 1560nm and the excited molecules undergo relaxation through non-radiative processes, which gives rise to transient thermal effects. These transient thermal effects are related to the pure optical nonlinearity of the samples and can be measured as a change in their n2 values [14]. The transient thermal effects of individual pulses accumulate in case of high repetition-rate lasers to produce a cumulative thermal effect at longer timescales. We measure this cumulative thermal effect with the mode-mismatched two-color pump–probe experiment.