Sum frequency generation spectroscopy (SFG) is a technique used to analyze surfaces and interfaces. This nonlinear laser spectroscopy method can deduce the composition, orientation distributions, and some structural information of molecules at gas–solid, gas–liquid and liquid–solid interfaces. In a typical SFG setup, two laser beams mix at a surface and generate an output beam with a frequency equal to the sum of the two input frequencies. SFG has advantages in its ability to be monolayer surface sensitive, ability to be performed in situ (for example aqueous surfaces and in gases), and not causing much damage to the sample surface. SFG is comparable to second harmonic generation in Infrared and Raman spectroscopy. It is a challenge to measure orientation heterogeneity. For decades, surface-specific vibrational sum frequency generation spectroscopy (referred to as 1D VSFG hereafter) has been used to determine the mean tilt angle, under the assumption of a narrow orientational distribution. However, in this case, the knowledge of orientational distribution is lost, and the measured mean tilt angle can deviate from the real mean tilt angle when the orientational distribution is large, which is the well-known “magic angle” challenge.