We grew pentacene crystals via physical vapor transport as previously described. Briefly, we annealed a home built physical vapor transport chamber overnight at 350 °C. Then, we placed pentacene powder (Sigma Aldrich, CAS #135-48-8) in a glass boat at one end of the chamber and heated the chamber to 100 °C for one hour. We created a temperature gradient across the chamber by heating the sample end of the chamber to 310 °C and the opposite end to 272 °C. We flowed with argon gas at 100 mL/min for 2 hours, and then let the chamber return to room temperature. We mounted the crystal in superglue between two glass coverslips to prevent photodamage. We selected crystals for FSRS measurements based on shape and thickness-a opaque crystal shaped like a parallelogram with sharp edges and corners, indicating a single crystal with high optical density. We used polarized spontaneous Raman spectroscopy to identify the relative orientation of the crystallographic axes (Fig. ). We present the UV-vis absorption spectrum for the crystal used in this study in Fig. . We note that thinner crystals seemed more susceptible to photodamage, and we ensured that the overall damage was minimal as evidenced by a loss of ground state stimulated Raman signal of less than 14% over 4 hours of measurements.