optical parametric oscillator (OPO)

light source similar to a laser, but based on 'non-linear optical gain' from parametric amplification rather than on stimulated emission.
  1. The device is a powerful solid-state source of broadly tunable @C01130@. It consists of a crystal, usually BBO (BaB2O4), located inside an optical resonator and pumped by a very intense @L03459@ beam (typically provided by a pulsed @N04103@ or a @D01747@). The pump beam (@W06659@ λp frequency ν p) is partially converted into two coherent beams, the signal and the idler, with wavelengths (λs, λI) and frequencies (ν s, ν I) such that ν s + ν i = ν p. By simultaneous rotation of the crystal and adjustment of the optical resonator, the @W06659@ of the signal beam is continuously tunable, theoretically from λp to 2 x λp and practically over a slightly more reduced range.
  2. For example, for λp = 355 nm (3rd harmonic of a Nd:YAG @L03459@), ν s can be tuned from 400 nm (with λi ≈ 3.15 µm) up to 600 nm (with λi ≈ 870 nm).
  3. This 'splitting of one photon into two photons' is the reverse of the 'sum frequency mixing' used, for instance, to generate the 3rd harmonic of a @L03459@ emission by mixing in a convenient crystal the fundamental and the frequency doubled beams (a way to get the 3rd harmonic much more efficiently than by pure frequency tripling as described under @H02744@).
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 378 (https://doi.org/10.1351/pac200779030293)