Mode-Selective Phonon Excitation of SrTiO3 by MIR-FEL with Anti-Stokes Hyper-Raman Scattering Spectroscopy

The selective excitation of LO3 phonon mode among seven optical phonon modes of strontium titanate (SrTiO
3
) by using a mid-infrared free electron laser (MIR-FEL) which will then be investigated and confirmed by anti-Stokes hyper-Raman scattering spectroscopy using pico-second laser is proposed to be done. The experiment on a single crystal of SrTiO
3
has been measured in the room temperature, and the Stokes hyper-Raman spectrum of the LO3 phonon mode was clearly observed at 800 cm
^-1
. However, the intensities of the spectra of this target phonon is very small even for the Stokes side that it is nearly impossible to observe the anti-Stoke spectrum with this experimental setup. The peak observed around 500 cm
^-1
is to be further investigated whether anti-Stokes hyper-Raman scattering or not and signal intensity increment measurements are to be done to perform mode selective phonon excitation by MIR-FEL.