Patent ID: 8369002

Claim:
A terahertz wave generating method comprising the steps of: (a) providing a first laser beam and a second laser beam incident on a difference frequency mixing unit and overlapping the two laser beams in the difference frequency mixing unit, and (b) generating a terahertz wave whose frequency is a frequency difference between the two laser beams, wherein the first laser beam has a spatial spread in a predetermined direction and a spatial frequency distribution of the first laser beam is a distribution in which a magnitude of a frequency gradually increases in a frequency gradient direction which is the predetermined direction, the second laser beam also has a spatial spread in the frequency gradient direction and a spatial frequency distribution of the second laser beam is also a distribution in which a magnitude of a frequency gradually increases in the frequency gradient direction so that the frequency difference between the two laser beams is equal in each position in an overlapping region of the two laser beams, and the terahertz wave of a single frequency is generated from the overlapping region, and wherein the first laser beam and the second laser beam are spatially shifted with respect to each other in the frequency gradient direction to change the frequency difference in the overlapping region, thereby changing the single frequency.