Abstract: An optical probe system is disclosed for in situ optical spectroscopy and photoluminescence measurements on high-temperature reactions. The system includes an optical probe comprising an optical housing, a main probe body, and an adjustable solution window. The optical housing is thermally isolated and houses a collimating lens for coupling light from a source. The main probe body includes a transparent waveguide and a protective sleeve, while the adjustable solution window incorporates a mirror for reflecting light back to a fiber optic, with an adjustable path length. The system may also include a heatbreak for thermal isolation, a hermetic sealing ring, and a tilt-translate mechanism for lens alignment. The system may also provide a bifurcated optical fiber, spectrometer, color balancing filter, and multiple light sources for switching between spectroscopy across UV, Vis, and IR spectra and PL measurement.