Incoherent scattering refers to the random scattering of waves or particles where the phase relationships between the scattered waves are lost. A common example of incoherent scattering occurs in rough surfaces or dense media where incident waves interact with numerous scattering centers that cause phase randomization.
For example, sunlight scattered by the moon’s rough surface exhibits incoherent scattering, leading to diffuse reflection and loss of phase coherence among the scattered waves.
Coherent diffusion, on the other hand, involves waves that maintain a fixed phase relationship after diffusion. One example is Bragg scattering, observed in crystal lattices where X-rays or neutrons scatter atoms within the lattice structure.
The fixed phase relationship between incident and scattered waves allows constructive interference, resulting in distinct diffraction patterns that provide valuable information about the atomic structure of the material.
The main difference between coherent and incoherent scattering is the preservation of phase relationships. In coherent scattering, phase coherence between incident and scattered waves is maintained, enabling constructive or destructive interference patterns that provide detailed information about the scattering medium.
In contrast, incoherent scattering involves random phase relationships between scattered waves, leading to diffuse scattering patterns without discernible interference effects. Coherent scattering is usually associated with regular structures like crystals, while incoherent scattering occurs in irregular or dense media where phase coherence is lost due to multiple scattering events.
Raman scattering is an example of incoherent scattering. In Raman scattering, incident photons interact with molecules, causing them to undergo energy changes and emit photons with different energies.
The scattered photons are not in phase with the incident photons and exhibit random phase relationships. This characteristic makes Raman scattering useful for analyzing molecular vibrational modes and identifying molecular compositions based on scattered wavelengths.
Compton diffusion is another example of incoherent diffusion. It occurs when photons (usually X-rays or gamma rays) interact with free electrons in materials, transferring some of their energy to the electrons and scattering at different angles.
Scattered photons do not maintain a fixed phase relationship with incident photons due to the random nature of electronic interactions. Compton scattering is essential to medical imaging, astronomy, and materials science for studying electron densities and material compositions based on the energies and angles of scattered photons