1. A method of monitoring a high pressure reaction system comprising: (a) forming a polymerization material comprising: (i) a reaction mixture comprising monomer, solvent, and polymer product within a reaction zone maintained at a temperature of 120° C. to 355° C. and a pressure of 110 MPa to 350 MPa and (ii) polymer product downstream of the reaction zone; (b) irradiating at least a portion of the polymerization material; (c) measuring the energy shift experienced by the at least a portion of the polymerization material due to the step of irradiating; and (d) determining a characteristic of the at least a portion of the polymerization material based on the energy shift; wherein the at least one analysis probe has a focus point of about 50 μm to 200 μm for non-homogeneous polymerization materials and a focus point of about 400 to 700 μm for homogeneous polymerization materials.