False spectra from a plane grating produced by laser illumination

False spectra produced by intense coherent illumination are studied. This paper presents the well-known geometrical scheme to explain the formation and location of false spectral lines or Rowland ghosts, and from that scheme it was found that the number of ghosts produced by a spectral line is limited. This number is the same for the blazed region of the grating as for the unblazed one, and it includes the Rowland ghosts produced by the line at different spectral orders of the grating. Rowland's formula, derived on the basis of the geometrical scheme, may be used to calculate ghost wavelengths far away from the parent line. The formula was experimentally checked. Experiments were performed by using a pulsed ruby laser as a light source, and the extreme ghosts were recorded at 1336.9 A and 10761.5 A.