Parametric generation using intersecting cavities

1. A parametric device having a non-linear material for generating idler and signal waves in response to a pump wave, the pump, idler and signal waves being non-collinear, the device having a cavity resonant at the pump wavelength and which contains the nonlinear material, and means for varying the angle between the propagation directions of the pump and idler waves.

2. A device as claimed in claim 1 , wherein the cavity resonant at the pump wavelength contains the gain medium of the pump laser.

3. A device as claimed in claim 1 , wherein the cavity resonant at the pump wavelength is such as to resonantly enhance a pump wave generated by an external pump laser.

4. A device as claimed in claim 1 comprising a cavity that is resonant at the idler wavelength.

5. A device as claimed in claim 4 , wherein the wavelength of the idler wave is determined by injection into the nonlinear material of a seeding wave from an external source.

6. A device as claimed in claim 1 , wherein the direction of propagation and wavelength of the idler wave is determined by injection into the nonlinear material of a seeding wave from an external source.

7. A device as claimed in claim 2 , wherein the direction of propagation and wavelength of the idler wave is determined by injection into the nonlinear material of a seeding wave from an external source.

8. A device as claimed in claim 3 , wherein the direction of propagation and the wavelength of the idler wave is determined by injection into the nonlinear material of a seeding wave from an external source.

9. A device as claimed in claim 1 arranged to generate terahertz radiation.