Optical Limiting Due to Frequency Up-Converted Fluorescence in DASPB Dye Doped Polymer Film

4 -[4 - (Dimethylamino) styryl) - 1 - docosyl pyridinum bromide ](abbreviated as DASPB) is a nonlinear dye which shows strong two-photon absorption (TPA) and subsequent frequency upconversion fluorescence behavior when excited with near infrared radiation. The dye possesses a much larger TPA cross section and much stronger upconversion fluorescence emission than those of common organic dyes (such as rhodamine). In order to increase the concentration of absorptive or fluorescent centers as well as the optochemical and optophysical stability and effective use of this highly nonlinear dye, it has doped in methyl methacrylate - methacrylic acid co-polymer (PMMA-MA). Linear absorption spectrum, single photon induced fluorescence spectrum and two photon induced fluorescence at different wavelength are studied. The nonlinear optical transmission at both linear absorption region and linear transmission region are studied using nano and pico second laser pulses. The optical limiting behavior of the dye is also studied in cw, pico and femto second region. Using Z-scan studies it is found that in linear absorption region, the DASPB doped in PMMA-PA shows saturation absorption at lower intensity and reverse saturated absorption at higher intensity. At transmission region above 800 nm, it has shown the absorption due to two photon induced fluorescence as well as reverse saturation absorption. With experimental results, the molecular TPA cross-sections and TPF cross-section of the sample are calculated.