metric Oscillator - Beckman Institute Laser Resource Center

APump Signal Idlerm355 nm 400 nm 710 nm 2000 nm WavelengthInput PulseFigure 1-3: Signal and ldler Output wavelengths for 355nm PumpIn the MOP0 system, the pump wavelength hp is always 355nm. In theory,however, an infinite number of signal and idler wavelengths exist to satisfy equation (1).The angular dependence of the birefringence in anisotropic crystals, suchas BBO results in a variation of refractive index as the crystal is rotated. By fixingthe pump wavelength and beam path, any variation in signal and idler index ofrefraction caused by a rotation in the crystal will vary the wavelength resonated withinthe cavity, thus allowing tuning to be accomplished.For further information on OPO theory, refer to "Tunable OpticalParametric Oscillators" by Steven E Hanis, Proceedings of the IEEE, Volume 57,No. 12, December 1969, p. 2096-2113.BBO Enables OPO Commercia/izationThe commercialization of OPO technology has taken more than 25 years due to thelack of suitable, commercially available nonlinear materials. In order for a materialto be suitable for OPO use, the crystal must possess five critical properties simultaneously:Phase matching conditions for pump, signal and idler wavelengths over the tuningrange of interest.High damage threshold to sustain the intense pump fluence required for thenonlinear interaction.Low absorption over the entire tuning range.Ability to be fabricated in useful sizes.No significant degadation with time.The only material fitting these criteria is BBO, and it has only been inrecent years that high quality BBO crystals have been available in useful sizes necessaryfor the commercialization of OPO devices.