Ultraviolet 363.8-nm Raman Spectroscopic System for in Situ Measurements at High Temperatures

Abstract

A new ultraviolet (UV) Raman spectroscopic system to measure the Raman scattering from materials at high temperatures up to 1500 °C has been designed. This system is based on a CW (continuous-wave) ultraviolet argon-ion laser (363.8 nm), a spatial filter, a single monochromator coupled to a double-grating rejection filter, and a two-dimensional charge-coupled device (CCD) detector. The plasma lines from the laser are almost completely rejected by a Pellin—Broca prism combined with apertures. In situ Raman measurements for a zirconia (ZrO₂) specimen at various high temperatures have been performed by using the UV excitation as well as the conventional visible 488.0-nm excitation for comparison. In the case of visible excitation, thermal emission obstructs the observation of the Raman scattering from zirconia even at 900 °C; it becomes rapidly pronounced between 900 and 1100 °C, and finally it is impossible to observe Raman spectra at temperatures higher than 1200 °C. In sharp contrast to the visible excitation, the UV excitation provides good-quality Raman spectra with practically flat backgrounds for the Raman signal of tetragonal zirconia in the spectral region of 20–1100 cm⁻¹ even at 1500 °C, and it enables clear observation of the monoclinic-tetragonal phase transformation of zirconia occurring between 1100 and 1200 °C.