Fiber probe is used to collect light or spectra from extreme environments inside reaction vessels at high temperatures or pressures. The type of fiber probes includes UV-Vis spectroscopy probes and refractometry probes. UV-Vis spectroscopy probes track the electronic transitions of molecules as they absorb light in the ultraviolet and visible regions of the electromagnetic spectrum. These fiber optic probes can be used with a wide range of samples and are suitable for biochemical, biological, and pharmaceutical research. Refractometry probes are fiber optic probes that detect the deviation of light by a solution as a measure of specific gravity.