We have demonstrated highly efficient frequency doubling of femtosecond pulses in a thick, noncritically phase-matched KNbO<sub>3</sub> crystal under conditions of large group-velocity mismatch. At low power we observed a slope efficiency of ∼300% nJ <sup>-1</sup> for harmonic conversion, and at higher powers we generated 170 mW of second-harmonic blue output for 300 mW of input light. Furthermore, we have shown that the focusing dependence for our conditions of large group-velocity mismatch is considerably different from that obtained for frequency doubling of continuous-wave light. We have also demonstrated that one can tune the spectral width of the generated blue light by varying the focusing conditions.
© 1998 Optical Society of America
(190.0190) Nonlinear optics : Nonlinear optics
(190.2620) Nonlinear optics : Harmonic generation and mixing
(190.4160) Nonlinear optics : Multiharmonic generation
(320.0320) Ultrafast optics : Ultrafast optics
(320.2250) Ultrafast optics : Femtosecond phenomena
A. M. Weiner, A. M. Kan’an, and D. E. Leaird, "High-efficiency blue generation by frequency doubling of femtosecond pulses in a thick nonlinear crystal," Opt. Lett. 23, 1441-1443 (1998)