Theoretical study of the recording density limit of photochemical hole-burning memory

To clarify the potential of photochemical hole-burning memory systems, we study the theoretical recording-density limit of such systems. Shot noise and material noise are considered the principal noises. Material noise originates in fluctuations in the chromophore concentration. The recording-density limit proves to be proportional to (multiplicity)1/2 × (chromophore concentration)1/2 × (hole depth), approximately. It becomes clear that the recording spot diameter can be optimized to maximize the recording density. A molar extinction coefficient for a chromophore can be also optimized, and its value is ∼105 L/(mol cm) under the conditions of a 0.2 hole depth, 1000 multiplicity, and 10−2 mol/L choromophore concentration. When the readout time is 10 ns/bit and the signal-to-noise ratio is 20, in addition to the above conditions, the recording-density limit is calculated to be 26 Gbits/cm2. For this readout time the optimal recording spot diameter is ∼2 μm. When the readout time is less than ∼10 ns/bit, shot noise becomes the dominant noise; when the readout time is more than ∼50 ns/bit, the recording-density limit increases, and the influence of material noise becomes prominent.