optical parametric oscillator (OPO)

@L03526@ similar to a @L03459@, but based on 'non-linear optical gain' from @PT07440@ rather than on @S06015@.
  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@ \(\lambda_{\text{p}}\) frequency \(\nu_{\text{p}}\)) is partially converted into two coherent beams, the signal and the idler, with wavelengths (\(\lambda_{\text{s}}\), \(\lambda_{\text{l}}\)) and frequencies (\(\nu_{\text{s}}\), \(\nu_{\text{l}}\)) such that \(\nu_{\text{s}} + \nu_{\text{i}} = \nu_{\text{p}}\). By simultaneous rotation of the crystal and adjustment of the optical resonator, the @W06659@ of the signal beam is continuously tunable, theoretically from \(\lambda_{\text{p}}\) to \(2 \times \lambda_{\text{p}}\) and practically over a slightly more reduced range.
  2. For example, for \(\lambda_{\text{p}} = 355\ \text{nm}\) (3rd harmonic of a Nd:YAG @L03459@), \(\nu_{\text{s}}\) can be tuned from \(400\ \text{nm}\) (with \(\lambda_{\text{i}} \approx  3.15\ \unicode[Times]{x3BC}\text{m}\)) up to \(600\ \text{nm}\) (with \(\lambda_{\text{i}} \approx 870\ \text{nm}\)).
  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 [Terms] [Paper]