Vp. Kozich et al., DUAL-BEAM TIME-RESOLVED Z-SCAN IN LIQUIDS TO STUDY HEATING DUE TO LINEAR AND NONLINEAR LIGHT-ABSORPTION, Applied spectroscopy, 48(12), 1994, pp. 1506-1512
Dual-beam extension of a Z-scan technique has been developed to study
the thermal changes in the refractive index resulting from linear and
nonlinear absorption in liquids. The experiments were carried out with
nanosecond-pulsed Nd:YAG radiation and its second harmonic as the exc
itation sources and a He-Ne laser as the probe beam. The cw probe radi
ation enabled us to observe temporal dynamics of the refractive index
variations, to select the thermal signal for Z-scan measurement and to
measure absolute changes in the refractive index as small as 10(-6) d
ue to heating in a number of organic liquids. The temporal shape of th
e thermal signal is analyzed experimentally and theoretically both in
weak and strong phase distortion of the probe wave. Gaussian approxima
tion for the pump and probe beams and the Taylor series decomposition
of nonlinear phase distortion term at the exit of the sample are used
to describe the thermal signal and to fit experimental data to theoret
ical models.