Digital cold strain engineering: photon forging via GHz sub-pulse programming

The application of strain engineering in amorphous oxides is fundamentally impeded by crystallization and mechanical damage, thereby limiting device performance. To overcome this, we introduce digital cold strain engineering (DCSE), which utilizes GHz-frequency femtosecond pulse-sequenced photonic forging for nonthermal dominant, stress-mediated modification. By programming the sub-pulse number under constant laser power, DCSE generates a controllable ultrafast stress field that enables stress-mediated modification of the amorphous network while preserving the predominantly amorphous character of the film and suppressing pronounced ablation craters. Multimodal characterization indicates amorphous phase preservation within the detection limit, accompanied by reduced surface roughness and film thickness as well as an elevated refractive index. The correlated shifts in the Ga 3d and O 1s binding energies suggest that laser-induced modification of the amorphous network and changes in the local electronic environment may contribute to the blue shift of the optical absorption peak from 263 to 256 nm. The representative photodetector exhibited ∼57% higher photocurrent, ∼58% higher responsivity (∼0.126 versus ∼0.080 mA/W), and ∼25% improved detectivity (∼5.5×109 versus ∼4.4×109 Jones). DCSE thus presents a promising strategy for programmable structural and electronic modification of amorphous materials, offering a route toward tunable functional-material design through discrete laser pulse programming.