Electric field periodically inverted LiNbO3 for optical frequency conversion
This thesis describes work carried out at Southampton on periodic poling of LiNbO3. Periodically poled LiNbO3 (PPLN) samples have been fabricated using standard lithography processes and high voltage pulses applied via liquid electrodes. The nonlinear grating associated with the periodic domain inversion provides a means for efficient quasi-phase-matched second-order nonlinear optical processes, such as second harmonic generation (SHG) and optical parametric oscillation (OPO). Compared to birefringent phase-matching, traditionally used, quasi-phase-matching offers several advantages, such as access to higher nonlinear coefficients, non-critical interaction geometry, wider range of interaction wavelengths and reduced photorefractive damage. The fabrication of PPLN together with its optical assessment and the description of the nonlinear optical devices based on this novel material form the content of this thesis. SHG to the blue and to the green have been efficiently performed in PPLN in cw, Q-switched and mode-locked regimes. Also OPO, Q-switched and mode-locked pumped, is reported. Particular emphasis has been given to the study of the photorefractive effect in PPLN. Along the way we discovered a new type of self-organised light-induced scattering, typical of PPLN. This thesis points out that PPLN is already an effective nonlinear medium for quasi-phase-matched frequency conversion with great prospects for future improvement.