Nonlinear optical investigations of the polymer sufaces modified by the UV-laser illumination.

An essential influence of the nitogen laser (λ = 337 nm) photon pluxes, UV-light time exposure and temperature on the behaviour of corresonding nonlinear optical susceptibilities obtained from surfaces for different types of polymers was observed. Temperature dependencies show an existence of at least two components of second harmonic generaton (SHG) intensity. For all the specimens the increase of photoinduced SHG signal with decreasing temperature was revealed, which indicates on the possible low-temperature ordering of the samples under investigations. Correlation between the degree of crystallinity of corresponding surface and the values of SHG signals was revealed. The polyvinyl polymers with different contents of the appropriate organic and inorganic components are selected for investigation, and we report the results of the transient and reflected (SHG) study of the UV-light induced acentrial structural fragments in amorphous polymer surfaces. The data obtained unambiguosuly show that all the nonlinear optical properties are saused mainly by the surface crystallization. The obtained results indicate the possibility of using the obtained results for the investigations of the crystallinity degree of the polymer surfaces. Moreover, it is an effective method of non-contacting control of the structural instability in these materials. Simultaneously we have performed "ab initio" quantum chemical calculations in order to interpret the obtained optical spectra.