  Path integrals give a possibility to compute in details routes of particles
from particle sources through slit gratings and further to detectors. The path
integral for a particle passing through the Gaussian slit results in the
Gaussian wavepacket. The wavepackets prepared on N slits and superposed
together give rise to interference pattern in the near-field zone. It
transforms to diffraction in the far-field zone represented by divergent
principal rays, at that all rays are partitioned from each other by (N-2)
subsidiary rays. The Bohmian trajectories in the near-field zone of N-slit
gratings show wavy behavior. And they become straight in the far-field zone.
The trajectories show zigzag behavior on the interference Talbot carpet (ratio
of particle wavelength to a distance between slits are much smaller than 1 and
N>>1). Interference from the the N-slit gratings is simulated by scattering
monochromatic neutrons (wavelength=0.5 nm). Also we have considered simulation
of interference fringes arising at scattering on an N-slit grating of fullerene
molecules (according to the real experiment stated in e-print 1001.0468).
