Interference Effects in Femtosecond Sum Frequency Spectra of Model Cellulose Films

Application of sum frequency spectroscopy (SFS) to thin film structures results in complex spectra, which require theoretical deconvolution. In the present work, a new copropagating model for SF emission from model cellulose surfaces has been developed, thereby enabling the study of cellulose surface characteristics and various aspects of wood utilization. Immobilized model cellulose films have been prepared on gold-coated silicon wafers for characterization by SFS. Before quantitatively analyzing SF spectra derived from cellulose, the thickness-dependent interference effect between multiple SF sources in the cellulose/gold system was investigated theoretically. Comparisons between experimental and simulated SF spectra enable an accurate understanding of thickness/phase and thickness/intensity interference effects, which are essential to the application of SFS to cellulose and other thin films on gold. It was shown that the resonant SF signal generated at the cellulose/gold interface is small, is constant...