where λ is the particle wavelength, h is the Planck constant, and p is the particle momentum. From this, it follows that interference effects between particles of matter will occur. This forms the basis of the Kapitza–Dirac effect. Specifically, Kapitza–Dirac scattering operates in the Raman–Nath regime. This is to say that the interaction time of the particle with the light field is sufficiently short in duration such that the motion of the particles with respect to the light field can be neglected. Mathematically, this means the kinetic energy term of the interaction Hamiltonian can be neglected. This approximation holds if the interaction time is less than the inverse of the recoil frequency of the particle, τ τ ≪ ≪ 1 / ω ω rec . This is analogous to the thin lens approximation in optics. A coherent beam of particles incident on a standing wave of electromagnetic radiation (typically light) will be diffracted according to the equation: