optical parametric oscillator (OPO) 

Acronym: OPO
https://doi.org/10.1351/goldbook.OT07438
Light source similar to a laser, but based on 'non-linear optical gain' from parametric amplification rather than on stimulated emission.
Notes:
  1. The device is a powerful solid-state source of broadly tunable coherent radiation. It consists of a crystal, usually BBO (BaB2O4), located inside an optical resonator and pumped by a very intense laser beam (typically provided by a pulsed neodymium laser or a diode laser). The pump beam (wavelength λp frequency νp) is partially converted into two coherent beams, the signal and the idler, with wavelengths (λs, λl) and frequencies (νs, νl) such that νs+νi=νp. By simultaneous rotation of the crystal and adjustment of the optical resonator, the wavelength of the signal beam is continuously tunable, theoretically from λp to 2×λp and practically over a slightly more reduced range.
  2. For example, for λp=355 nm (3rd harmonic of a Nd:YAG laser), νs 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 laser 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 harmonic frequency generation).
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 378 [Terms] [Paper]
Citation: 'optical parametric oscillator' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.OT07438 RIS BibTex EndNote
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Last revised: February 24, 2014