Collimating properties of an axicon for the Cerenkov-radiation-type second-harmonic light from a crystal-cored fiber.

The optical second-harmonic wave generated from a crystal-cored fiber from the Cerenkov-radiation-type phase matching can be collimated by an axicon and then can be focused by a spherical lens to a diffraction-limited spot. Tolerance of the optical system to meet the Maréchal criterion is analyzed; tolerable maximum errors in alignment and fabrication of the axicon lens are evaluated.

Frequency doubling of a Nd:YAG laser using a crystal-cored fiber of an organic 4-(N,N-dimethylamino)-3-acetamidonitrobenzene.

Optical second-harmonic generation from a glass-clad fiber with an organic core crystal of 4-(N,Ndimethylamino)-3-acetamidonitrobenzene (DAN) is demonstrated. Phase matching was due to cerenkov radiation. Linear and nonlinear optical properties of DAN, a fabrication technique of a crystal-cored fiber, and a focusing method of the generated second-harmonic wave are studied.