## optical parametric oscillator

https://doi.org/10.1351/goldbook.OT07438
@L03526@ similar to a @L03459@, but based on 'non-linear optical gain' from @PT07440@ rather than on @S06015@.
Notes:
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@ $$\lambda_{\textrm{p}}$$ frequency $$\nu_{\textrm{p}}$$) is partially converted into two coherent beams, the signal and the idler, with wavelengths ($$\lambda_{\textrm{s}}$$, $$\lambda_{\textrm{l}}$$) and frequencies ($$\nu_{\textrm{s}}$$, $$\nu_{\textrm{l}}$$) such that $$\nu_{\textrm{s}} + \nu_{\textrm{i}} = \nu_{\textrm{p}}$$. By simultaneous rotation of the crystal and adjustment of the optical resonator, the @W06659@ of the signal beam is continuously tunable, theoretically from $$\lambda_{\textrm{p}}$$ to $$2 \times \lambda_{\textrm{p}}$$ and practically over a slightly more reduced range.
2. For example, for $$\lambda_{\textrm{p}} = 355\: \textrm{nm}$$ (3rd harmonic of a Nd:YAG@L03459@), $$\nu_{\textrm{s}}$$ can be tuned from $$400\: \textrm{nm}$$ (with $$\lambda_{\textrm{i}} \approx 3.15\: \mu\textrm{m}$$) up to $$600\: \textrm{nm}$$ (with $$\lambda_{\textrm{i}} \approx 870\: \textrm{nm}$$).
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@).
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 378 [Terms] [Paper]