Fig. 3

Time-dependent absorption (Abs.) coefficient (coeff.) spectrum of an initially amorphous NIF sample stored at (a) 24 °C, (b) 30 °C and (c) 35 °C. For clarity, every 4th measurement is shown, resulting in steps of approximately 14 min. Curves corresponding to approximately 0, 1, 2, 3, 4, 5 and 6 days are depicted as a black bold curve and plotted with an offset of + 2 cm⁻¹ for easier comparison. In total, five samples per storage temperature were examined, showing similar results.