Abstract
We study the requirements imposed on organic photochromes for two-photon absorption (2PA) terabyte volumetric optical storage. We present a quantitative model of signal-to-noise ratio (SNR) and signal-to-background ratio (SBR) when 2PA-induced photochromic switching is used for writing, and 2PA-induced fluorescence is used for readout. We show that single-channel data access rate >100 MHz at minimum SNR>4 implies minimum intrinsic 2PA cross section, σ2>103GM. Resonance enhancement allows σ2∼105GM, however, it also lowers SBR due to thermally-activated one-photon absorption. We model the critical trade-off between SNR and SBR as a function of laser frequency, intensity, and temperature. Acceptable parameter space may be achieved by careful choice of the above variables. We perform experiments with nonsymmetrical free-base phthalocyanines, which show efficient 2PA-induced photochromic switching between two tautomer forms and large σ2∼104GM, and show good potential for high-capacity data storage.
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