Continuously phase-matched terahertz difference frequency generation in an embedded-waveguide structure supporting only fundamental modes.

We demonstrate an all-single mode structure which enables continuous phase matching of difference frequency generated THz light from the near-IR. This structure provides a long interaction length by way of well-confined collinear propagation of pumps and product without diffraction, resulting in high conversion efficiency. A LiNbO(3) version of this structure achieved a power-normalized conversion efficiency of 1.3 x 10(-7) W(-1)--some 23 times larger than the largest previously reported results.