Experimental study of electric-field poling in LiNbO3 crystal by femtosecond laser carving

A novel technique of periodically poling in femtosecond laser treated LiNbO3 (LN) crystal is reported. Because of the precision of the femtosecond laser machine, the width and depth of snicks can be controlled exactly. Then the high voltage electric field was operated on +Z side of the LiNbO3 crystal. The visible poling pattern was observed by microscope. The machining parameter influence on the electric-field poling distributing in the crystal was investigated. Comparing with nanosecond laser carving, using femtosecond laser pulses the structure can be made more precisely with a larger deep-width ratio. The new technique does not need expensive and complicated mask and lithography, and periods of periodically poled lithium niobate (PPLN) can be adjusted flexibly. Although the mechanism of core formation is not clear yet, it would be a very useful technique in developing new type of periodically poled devices.