Proper analysis of vibrational sum-frequency generation (VSFG) spectra requires that the nonresonant contribution be dealt with correctly. This work shows that the temporal profile of the nonresonant SFG response varies with crystal facing and sample orientation for single-crystal Si and is significantly different than what is observed with polycrystalline Au. These considerations will affect the use of time-delay methods to experimentally suppress the nonresonant signal in broadband SFG measurements. Time-resolved or phase-sensitive SFG measurements will also need to properly account for these effects in post-processing.
Keywords: SFG; Sum-frequency generation; nonresonant SFG; temporal profile.