The substituent effect on pulsed laser beam self-action manifestation in azo-azomethine PMMA composites thin films in visible and near IR ranges

Efficiency of nonlinear optical response was studied for a set of azo-azomethines dyes with substituted electron-withdrawing/donating groups, being embedded in poly(methyl methacrylate) (PMMA) matrix, via self-action effects manifestation of mode-locked Nd:YAG laser single pulses in visible at 532 nm, and in near IR at 1064 nm ranges. Photoinduced variations of refractive index and optical absorption/bleaching are crucially dependent on electron-donating/accepting substituents' properties with |Re(χ (3) )| ∼ 10 −7 esu and | Im(χ (3) )| ∼ 10 −9 esu efficiencies correspondingly at moderate laser excitation up to 10 MW/cm 2 . Incorporation of the azomethine group has provided tendency for fractional self-focusing effect manifestation in visible range against reference Azo dye , while at 1064 nm – self-defocusing one. For some dyes magnitudes of |Re(χ (3) )| in near IR range are comparable and even higher than for the corresponding ones at 532 nm due to resonant cascaded three photon excitation into the peak vicinity of π→π∗ transitions of the dyes. It was established linear relationship between second-order hyperpolarizabilities under pulsed and CW laser excitation in visible range, being preliminary irradiated within full spectra of UV lamp for CW laser diagnostics mode. It proofs a suggestion that picosecond range single pulses transfer dyes into the same excited state as full spectrum of a mercury lamp irradiation – conventional tool for the smart molecules’ isomerization . Analysis of the experimental data has shown a high potential for the azo-azomethines dyes doped polymer composites in nonlinear optical applications. • Refractive and absorptive NLO response of azo-azomethines PMMA films were investigated via 1064/532 nm pulsed laser. • Refractive |Re(χ (3) )|∼10 −7 esu and absorptive |Im(χ (3) )|∼10 −9 esu responses are dependent on the substituents' nature. • Additional azomethine group provides a tendency for self-focusing effect manifestation at 532 nm against the reference Azo. • Linear relationship between 2 nd order hyperpolarizabilities under CW and pulsed laser excitation at 532 nm was shown. • Incorporation of the azomethine group tends to fractional self-defocusing effect at 1064 nm.