Dynamics of all-optical switching in polymethine dye molecules

All-optical switching has been analyzed in the recently reported Polymethine dye (2-[2-[3-[(1,3-dihydro-3,3-dimethyl-1-phenyl-2H-indol-2-ylidene)ethylidne]-2-phenyl-1-cyclohexene-1-yl] ethenyl]-3,3-dimethyl-1-phenylindolium perchlorate) (PD3) [O.V. Przhonska, D.J. Hagan, E. Novikov, R. Lepkowicz, E.W.V. Stryland, M.V. Bondar, Y.L. Slominsky, A.D. Kachkovski, Chem. Phys. 273 (2001) 235.] that exhibits large excited-state absorption, using the rate equation approach, to achieve high contrast and fast switching. The transmission of a cw probe laser beam (Ip) at 532 nm through PD3 dissolved in (i) ethanol and (ii) polyurethane acrylate (PUA), is switched by a pulsed pump laser beam at 532 and 650 nm, respectively, which excite molecules from the ground state. The theoretical results show good agreement with the reported experimental results for case (i). The switching characteristics have been shown to be sensitive to variation in concentration, pump pulse width (Δt), peak pumping intensity (Im0′), absorption cross-section of the excited-state at 532 nm and lifetime of excited-state (τ1). The same switching contrast can be achieved at relatively lower pump powers at 650 nm for case (ii). It is shown that there is an optimum value of concentration at which maximum modulation can be achieved. We can get 96% modulation of Ip at Im0′=1 GW/cm2 at 650 nm, with Δt=30 ps and concentration of 0.14 mM in PUA, resulting in switch off and on time of 95 ps and 18 ns, respectively. The results have also been used to design all-optical NOT and the universal NOR and NAND logic gates with multiple pump laser pulses, which are the basic building blocks of computing circuits.