Graphical illustration of the phase-matching condition in an optical-frequency convertor using lithium niobate

A graphical illustration is given of the phase-matching condition in optical parametric oscillators and frequency multipliers using lithium niobate. It clearly shows the importance of index matching in such a process. The authors explain why, at a given frequency, the working temperature varies from one lithium niobate monocrystal to another. One can thus obtain the relation giving the frequency of a parametric oscillator versus the temperature.