Since the Raman process is proportional to local electric field intensity , it makes sense that methods of enhancing the local field may enhance the Raman response. It is well-known in SERS experiments that when plasmonic nanoparticles aggregate, optical coupling between particles in the electromagnetic field becomes very strong, resulting in a significant increase in the local field near the particle. Particle dimension, state of aggregation, and geometry play a large role in determining enhancements in plasmon resonance spectroscopy. The incident light around the plasmon resonance peak wavelength is scattered very strongly, leading to the SER effect.