Near infrared excited micro-Raman spectra of 4 : 1 methanol-ethanol mixture and ruby fluorescence at high pressure

Near infrared (NIR) lasers, as a new excitation source for Raman spectrosco py, has shown its unique advantages and is being increasingly used for some special samples, such as those emitting strong fluorescence in the visible region. This article focuses on some issues related to high-pressure micro -Raman spectroscopy using NIR excitation source. The Raman spectra of 4:1 m ethanol-ethanol mixture (4:1 M-E) show a linear variation in both Raman shi fts and linewidths under pressure up to 18 GPa. This result is useful in di stinguishing Raman scattering of samples from that of the alcohol mixture, an extensively used pressure-transmitting medium. The R1 fluorescence in th e red region induced by two-photon absorption of the NIR laser is strong en ough to be used as pressure scale. The frequency and line width of the R1 l ines are very sensitive to pressure change and the glass transition of the pressure medium. Our results manifest that it is reliable and convenient to use NIR induced two-photon excited fluorescence of ruby for both pressure calibration and distribution of pressure in the 4: 1 M-E pressure transmitt ing medium. (C) 1999 American Institute of Physics. [S0021-8979(99)00210-8] .