A cell culture vessel, cell culture monitoring system, and Raman spectroscopy system for non-invasive measuring of a cell culture are provided. The vessel includes a cell culture chamber that operates as a closed system, a wall defining a boundary of the cell culture chamber and separating the interior space of the cell culture chamber from an exterior of the cell culture chamber, and a window disposed in the wall and separating the interior space of the cell culture chamber from an exterior of the cell culture chamber. The cell culture chamber includes an interior space for housing at least one of the cell culture and a cell culture media. The window includes a polymer and allows monitoring of the cell culture via a monitoring module disposed on the exterior without the monitoring module coming into physical contact with the cell culture or the cell culture media.