In this work, we report a comparative study of the nonlinear optical responses of CH₃NH₃PbX₃ (where X is a chlorine, bromine, or iodine halogen atom) perovskite thin (~200 nm) films using 40 fs, 800 nm pulses. We found that these films possess strong nonlinear absorption coefficients comparable with the highest reported values for thin film structures (up to 7 × 10⁻⁷ cm W⁻¹). We also analyze the photoluminescence emission from CH₃NH₃PbBr₃ film and demonstrate the quadratic dependence of emission intensity on the intensity of probe pulse indicating a two-photon mechanism of luminescence.

Gold films are widely used for different applications. We present the results of third- and high-order nonlinear optical studies of the thin films fabricated from Au nanoparticle solutions by spin-coating methods. These nanoparticles were synthesized by laser ablation of bulk gold in pure water using 200 ps, 800 nm pulses. The highest values of the nonlinear absorption coefficient (9 × 10⁻⁶ cm W⁻¹), nonlinear refractive index (3 × 10⁻¹¹ cm² W⁻¹), and saturation intensity (1.3 × 10¹⁰ W cm⁻²) were achieved using 35 fs, 400 nm pulses. We also determined the relaxation time constants for transient absorption (220 fs and 1.6 ps) at 400 nm. The high-order harmonic generation was studied during propagation of 35 fs, 800 nm pulses through the plasma during the ablation of gold nanoparticle film and bulk gold. The highest harmonic cutoff (29th order) was observed in the plasma containing gold nanoparticles.

There are different possibilities for the applications of gold nanoparticles in various areas of optoelectronics. Here we report the nonlinear optical studies of chemically prepared gold nanoparticle suspensions using femtosecond pulses. The nonlinear refractive indices, nonlinear absorption coefficients, and saturated intensities of the nanoparticles of different sizes are measured at the wavelengths of 400 and 800 nm. We also demonstrate the optical limiting of 800 nm, 60 fs pulses during propagation through these suspensions. The competition of saturable and reverse saturable absorption in the case of 400 nm radiation is analyzed. The intensity-dependent transformation from saturable absorption to reverse saturable absorption indicates that these gold nanoparticles can be useful for eye protection, pulse shaping and passive mode locking.