Stimulated Rayleigh and Brillouin scattering in a supercritical fluid

We report stimulated Brillouin and Rayleigh scattering experiments in n-hexane for a wide range of subcritical and supercritical temperature and pressure conditions, including the near-critical region. The measurements were performed in a cell designed for operation at conditions near or above the critical point. An injection-seeded Nd:YAG laser was employed as the pump laser and an external cavity diode laser as the probe laser. The use of 1064-nm light enhances stimulated Rayleigh scattering through direct thermal absorption. Analysis of the recorded spectra yielded the widths, shifts, and heights of the electrostrictive Brillouin, thermal Brillouin, and thermal Rayleigh peaks. Comparison of these features with theory has showed consistency with the theoretical predictions of the relationships between the heights and widths of the thermal Brillouin and thermal Rayleigh peaks. Remarkable structure and sudden changes in the behavior of the Brillouin shifts, widths, and heights were observed in the vicinity of the critical region.