Optical limiting properties of J-type dimeric phthalocyanine Cu and optical switching based on spatial self-phase modulation

Abstract

In this study, J-type dimeric copper phthalocyanine in dimethylformamide (DMF) was investigated to show strong nonlinear absorption due to the reverse saturable absorption (RSA) under single nanosecond pulses (16 ns at a wavelength of 532 nm), which significantly exceeds the lifetimes of excited states. In the case of a femtosecond laser, the effect of spatial self-phase modulation was observed, with no contribution from nonlinear absorption being found. The only linear absorption was detected under pulses of 140 fs at a wavelength of 790 nm. The femtosecond pulse repetition rate was 80 MHz which corresponds to a delay between single pulses of about 12.5 ns. Both analytical wavelengths used were outside the intense absorption region (Q- and B- bands) of J-type dimeric copper phthalocyanine in the UV/Vis/NIR spectrum. In the case of femtosecond laser radiation, a sufficient population of excited states was not achieved due to the low peak fluence (~ 0.03 mJ/cm2). For the single nanosecond pulses, the threshold fluence density was ca. 30 mJ/cm2. In the switch circuit, such material should be placed horizontally to exclude asymmetric thermal convection resulting from the gravity effect.