Terahertz wave generator

A terahertz wave generator comprising a nonlinear crystal capable of generating a terahertz wave based on a parametric effect, a pumping beam emitter that emits a pumping beam, a seed beam emitter that emits a seed beam, a convex lens disposed on an optical path of the seed beam and collecting the seed beam, a first collimator for adjusting a pumping beam emitted from the pumping beam emitter into a first collimated beam, a second collimator for adjusting a seed beam emitted from the seed beam emitter into a second collimated beam, a concave lens disposed between the seed beam emitter and the convex lens on the optical path of the seed beam, and a light guiding means for allowing the second collimated beam to pass the concave lens and thereafter, in parallel with an optical axis of the convex lens, to be incident on the convex lens, and moves the seed beam, with the concave lens, in a direction orthogonal to an optical axis of the convex lens, wherein the terahertz wave generator is configured so that the pumping beam and the seed beam are caused to be incident through an end surface of the nonlinear crystal to generate the terahertz wave and the second collimated beam, a diameter of which is increased by the concave lens and further collected by the convex lens, is caused to be incident on the nonlinear crystal so as to be superimposed on the first collimated beam on the end surface.