<title>Wideband tunable and multiple noncritical phase matchings in nonlinear optics</title>

Abstract

A general classification of the phase-matching (PM) conditions noncritical to frequencies and angular apertures of signal and pumping () radiations is given; the sumand difference-frequency generation processes in uniaxial and biaxial crystals are covered in this investigation. The multiple noncriticality conditions are analysed, and physical concepts on group, tangential, and conditional centers are introduced. It has been found that the group centers (GC) can be tuned over the entire transparency region of the KTIOPO4 (KTP) crystal when changing , and the GC-tuning curve is finished at the distinctive critical point of PM (CPPM) where the triple noncriticality of PM is realized under conditions of collinear interaction and the greatest nonlinearity. It is shown that near the GC in KTP the spectral width of PM can exceed the value of lO3cm', and the considerable magnitude of tuning is possible at small change in in the vicinity of the CPPM. The possibility of generating narrow-band and wide-band radiations using the wide-band (narrow-band) pump radiation in optical parametric oscillator (OPO) is estabilished. A new phenomenon of division of the GC region into three regions of a double noncriticality is found. Key words: noncritical phase-matching, sum- and difference-frequency generation, optical parametric oscillator, wide-band UP-conversion.