NONLINEAR CRYSTALS FOR TUNABLE COHERENT SOURCES

High-efficiency non-linear crystals suitable for the generation of coherent sources ranging from the deep ultraviolet to mid-infrared (0.16 to 5 μm) are explored. The key parameters for frequency conversion techniques (second-harmonic-generation, sumfrequency mixing, difference-frequency mixing, optical parametric oscillation (OPO) and stimulated Raman scattering) including tunability, beam quality, beam walk-off and the effective figure-of-merit are analysed. Materials selection rules for non-linear crystals (for wide transparency, high damage threshold, stability, low absorption and large figure-of-merit) are presented. Techniques using non-critical phase-matching, quasi-phase-matching, waveguided doubling and self-frequency doubling are explored. Features and applications of the new non-linear crystals of β-barium borate, lithium triborate (LBO), potassium titanyl phosphate (KTP), KNbO3 and MgO:LiNbO3 are presented and compared with other crystals. In addition to a critical review, this paper also presents some new results for the analysis of frequency-conversion efficiency, experimental data of OPO in KTP, LBO for frequency conversion using temperature-tuned non-critical phase-matching and green lasers from the diode-pumped self-frequency-doubling crystal of neodymium yttrium aluminium borate. © 1990 Chapman and Hall Ltd.