Figure 3.

Simultaneous phase-change processing and storage. Microscope images (50 μm × 42 μm in each case) of marks in the Ge₂Sb₂Te₅ sample after the execution of various arithmetic processes. From left to right the first three images show the mark after computing and extracting the result for the base-10 computation of 7 + 2, 14÷10 and 5–2. The fourth image shows the mark after computing and extracting the result of the base-16 addition 5₁₆+B₁₆. For the first two calculations a single excitation comprised a group of 25 × 85 fs optical pulses; for the subtraction calculation a single excitation comprised 50 × 85 fs pulses; for the base-16 calculation a single excitation was 16 × 85 fs pulses. The extraction of the stored result for each of these computations took the measured reflectivity change above the pre-determined threshold value (which was 5%, 5%, 4.5% and 5.4% respectively), so the final marks in each case look very similar. In normal operation the phase-change material is reset to its initial state whenever the threshold is exceeded; in our case this was carried out using a single 11.7 mJ/cm² 85 fs pulse that successfully reset the system to the amorphous phase, as can be seen in the fifth image from the left which shows the result of inputting 10 (25 × 85 fs, 3.61 mJ/cm²) excitations followed by a single 11.7 mJ/cm² 85 fs reset pulse. Also shown (far right image) for comparison purposes is the resulting mark after 12 excitations and without resetting; in this case the reflectivity change is ∼11% and the mark is clearly different, even to the eye.