Simple Pulse Optimization Technique using LaAlO₃/SrTiO₃ Nanojunctions

Accurate characterization of few-cycle laser pulses is a central challenge in ultrafast science. Conventional methods rely on complex interferometric or spectro-temporal techniques, which often obscures the underlying physics of the pulse-matter interaction. Here, we present a Simple Pulse Optimization Technique (SPOT), which utilizes a rewritable LaAlO3/SrTiO3 (LAO/STO) nanoscale photodetector to monitor pulse compression via a nonlinear optical response. The core physical mechanism hinges on a local inversion-symmetry breaking at the LAO/STO interface, which effectively converts the bulk third-order nonlinearity of SrTiO3, characterized by χ(3), into a localized second-order susceptibility χ(2) [1]. This engineered nonlinearity allows the device to respond sensitively to the pulse's peak intensity, providing an electrical signal correlated with pulse duration. We experimentally validate this approach by comparing the observed photocurrent maximum and the point of minimum pulse width independently determined by a commercial dispersion-scan (d-scan) system [2]. Our findings highlight a robust and simplified platform for ultrafast pulse optimization with nanoscale applicability, operational simplicity, and potential for integration into optical systems, underscoring the promise of oxide electronics for harnessing and probing nonlinear optical phenomena at the nanoscale.