Second harmonic generation of blue light in backswitch-poled lithium niobate.

摘要

Today, solid-state Nd:YAG, Nd: YVO₄ and Ti:sapphire lasers with 1-to-10-watt output powers are widely available. Enabled by progress in laser diodes, materials and packaging, these sources are efficient, reliable and compact. Similarly, advances in nonlinear optics have enabled the extension of these lasers to cover a broad spectral range—from green to mid-infrared wavelengths.; Quasi-phasematching (QPM) is a nonlinear optical (NLO) technique now widely employed on a host of materials (e.g., LiNbO₃, LiTaO ₃ and KTiOPO₄) for achieving efficient optical frequency conversion. In this approach, the structure of the NLO medium is periodically altered, typically on the scale tens of microns, to correct for k -vector mismatch between the interacting optical waves. For ferroelectric materials, QPM is ordinarily accomplished by the technique known as electric field poling. This technique is well established for the fabrication of periodically poled lithium niobate (PPLN) with periods down to 6.5-μm for green light generation. Because of the large effective NLO coefficient of PPLN, d _eff ≈ 21 pm/V, it continues to attract interest as a QPM material for the generation of blue and ultraviolet (UV) wavelengths. However, extending electric field poling in PPLN to shorter periods, useful for blue and UV generation, has generally remained elusive.; This dissertation focuses on recent progress in PPLN and its application toward second harmonic generation (SHG) of blue light. A new electric-field poling technique, utilizing spontaneous backswitching, is introduced as a means for achieving shorter QPM periods than those attainable by the convention poling process. Using backswitched PPLN, single-pass SHG at 460 nm produced over 60 mW from continuous-wave (cw) Ti:sapphire and diode laser sources, and yielded 0.5 W with 59% efficiency from a cw-modelocked laser. Blue light sources such as this could find applications in displays, printing and optical data storage.