It is reported that scientists from the Tokyo Institute of Technology in Japan and the Kyoto University Institute of Material-Cell Integration Sciences used femtosecond visible light and terahertz pulses as external perturbations to study the second harmonic generation effect of light-excited bismuth oxide. This study highlights the importance of ion orbital excitation; this study is driven by terahertz radiation pulses and provides clues to improve the performance of nonlinear optical phenomena of nonlinear crystals on the femtosecond time scale.
Using SHG to double the frequency of the laser pointer (thus changing its color) requires reversing the polar crystal whose symmetry is destroyed. In view of this, it is an important research topic to identify the SHG crystals that can trigger strong, so this characteristic can be used in the field of materials science. Observing non-linear optical phenomena like SHG requires a limited second-order polarizability, which occurs inside any polar structure, intense laser, or pulse without inversion symmetry. In the perovskite-type cobalt oxide used in this study, the test unit exhibited apex oxygen displacement along the c-axis and Co-O5 cones, resulting in symmetrical fractures and extreme spontaneous polarization at room temperature.
For laser pulses only, strong electromagnetic pulses developed by the team with an electric field of up to about 1 MV / cm in the terahertz energy region can be used to achieve ultrafast control of nonlinear behavior.
Tokyo University of Technology in Japan specializes in the change in the intensity of SHG of BiCoO3 crystals when irradiated with a terahertz laser pulse at room temperature. It is worth noting that SHG has achieved an unprecedented enhancement of more than 50%, indicating that using a terahertz green laser pointer in this way can significantly improve the quality factor of nonlinear crystals. In addition, this effect occurs on the 100fs time scale, indicating that this property can be applied to ultrafast optoelectronic devices. Future research on the photo-excited state of BiCoO3 and other polar oxide materials will consider higher-order nonlinear optical responses and ultrafast structure measurements using terahertz pulses to clarify more technical details of these fascinating materials.