Abstract
Continuous-wave optical parametric oscillators (OPOs) combine single-frequency operation with a huge tuning range. Thus, they have emerged as working horses for spectroscopy in the near and mid infrared over the last decades [1]. However, in the terahertz range prominent nonlinear materials like lithium niobate have strongly damped phonon resonances leading to huge absorption. Consequently, the generation of terahertz waves by optical parametric oscillation requires around 100 W of near-infrared pump light exceeding the power delivered by standard single-frequency lasers. In a proof-of-principle experiment, we have demonstrated that this problem can be solved by the following cascade [2]: The primary process converts the pump wave into the primary idler and the primary signal wave at the frequency ν0. The latter one is cavity-enhanced and acts as a pump wave for a secondary process generating the secondary signal at ν1 and the far infrared secondary idler wave at νTHz = ν0 ν1. The output power of the terahertz field is limited by the Manley-Rowe relation to . In the − photon picture, this is interpreted in the following way: From one photon at ν0 exactly one photon at νTHz is created and thus, most of the power goes to the generated field at ν1 because ν0 ≈ ν1 ≈ 200 THz and νTHz ≈ 1 THz. Our latest studies show that higher pump powers can lead to higher-order cascaded processes suggesting that the output power of the terahertz wave can exceed the Manley-Rowe limit of a single parametric process.
© 2011 Optical Society of America
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