Walk-off effects, originating from the difference between the group and phase velocities, limit the efficiency of nonlinear optical interactions. While transverse walk-off can be eliminated by proper medium engineering, longitudinal walk-off is harder to avoid. In particular, ultrafast twin-beam generation via pulsed parametric down-conversion and four-wave mixing is only possible in short crystals or fibres or in double-path schemes. In our recent experiments, we have shown that in high-gain parametric down-conversion, one can overcome the destructive role of both effects and even turn them into useful tools for shaping the emission. In one of our experiments, the signal beam is emitted along the pump Poynting vector; in another one, group velocity of the signal beam matches that of the pump. The result is dramatically enhanced generation of both signal and idler twin beams, with the simultaneous narrowing of angular and frequency spectrum. The effect will enable efficient generation of ultrafast twin photons and beams in cavities, waveguides, and whispering-gallery mode resonators. It also provides a source of tunable broadband radiation with high directivity, which can be considered as an OPO without a cavity.

Seminar, April 16, 2015, 15:00. Seminar Room

Hosted by Prof. Morgan Mitchell