Low-frequency Raman spectrometer

The Raman scattering signals in the low-frequency (<200 cm^-1) region provides wealth information on intermolecular vibrations such as lattice vibrations, phonons and protein backbone vibrations, allowing us to study the intermolecular interactions in the condensed phase. However, conventional Raman spectrometers often struggle to detect the low-frequency Raman signals due to immense Rayleigh scattering and the limited bandwidth of the notch filter.

At USIL, we have overcome these challenges by combining a single-mode Nd:YVO4 laser (532 nm) with the BragGrate notch filters, enabling us to observe Raman signals down to 9.8 cm^-1 in both Stokes and anti-Stokes regions. This setup enables simultaneous recording of Stokes and anti-Stokes Raman signals, facilitating the use of their intensity ratio to estimate molecular temperatures based on Boltzmann distribution.

Furthermore, our setup incorporates an optical microscope (iX71, Olympus) equipped with a two-axes motorized translational sample stage, which enables Raman imaging measurements with sub-µm spatial resolution. This low-frequency Raman microspectrometer is particularly effective for monitoring phase transitions and distinguishing between different crystal structures.