Ultrafast Optical Dynamics in LRO/STO Heterostructure

To realize the coherent phonons and optical birefringence manipulation in the LRO/STO structure, time‐resolved optical reflectivity (TR‐ΔR) measurement with two pump pulses was performed. The LRO/STO (110) sample was kept at room temperature. The light source was a Ti:sapphire pulse laser with a wavelength of 800 nm, a repetition rate of 1 kHz, and a pulse duration of 100 fs. A beam splitter was used to divide the laser output into two parts. After converting the pump pulse wavelength to 400 nm with a BBO by second harmonic generation (SHG) process, the pump beam was further divided into two optical beams by another beam splitter. To control the time delay between the pump pulses of the two beams (Δt), a delay stage (DS2) was placed in the one of pump beams. A positive sign of Δt means that the pump pulse of the beam that passed through DS2 (the “second” pump pulse) arrived later at the sample surface than the pump pulse of the other beam (the “first” pump pulse). The relative delay (t) between the first pump pulse and the probe pulse is scanned by the DS1 delay stage. The incident angle of the probe beam is ≈45^o with respect to the normal direction of the sample plane, while the pump was ≈35° to the surface normal. The beam sizes are the same as the single pump experiment as mentioned above. Both pump 1 and pump 2 fluences are 9.6 mJ cm⁻². The experimental configuration of the signal detection part is consistent with that of the time‐resolved light reflectivity and optical birefringence effect experiment.