Novel quasi-phase-matched devices in periodically poled lithium niobate.

摘要

The ability to engineer novel quasi-phase-matched (QPM) structures in bulk periodically poled ferroelectric crystals has led to the development of a wide variety of innovative QPM devices. Lithium niobate has been the material of choice in many of these devices due to its large nonlinear coefficient (d₃₃ ∼ 27 pm/V), low cost, and wide availability. However, its large coercive field (∼21 kV/mm) has limited fabrication of periodically poled lithium niobate (PPLN) samples to a maximum thickness of ∼1 mm. This crystal aperture limitation combined with the low damage fluence of lithium niobate has restricted pulsed PPLN systems to low energy operation. In this thesis, we circumvent these limitations through innovative QPM grating designs and pumping schemes.; In this work we report the design, fabrication, and demonstration of three novel PPLN devices. The first device generated broadband mid-infrared radiation by using highly elliptical beams to pump PPLN crystals with a fan-out grating design. The signal and idler beams were spatially and angularly chirped while covering spectral bands as large as 3900 cm−1. The endfaces of the crystals were polished plane-parallel to force the system to operate in a monolithic optical parametric oscillator configuration. The second device used stacks of segmented multi-grating PPLN crystals to produce large signal energies with excellent beam quality. Signal energies as high as 33 mJ were generated in uncoated lithium niobate. In pursuit of the design for this system, we also explored several other unique QPM structures. The final device reported in this thesis is a widely tunable two-frequency injection-seeded optical parametric generator (OPG). In this two-stage system the output from the first stage was filtered to generate two narrow spectral lines. These lines were then used to seed the OPG process in the second stage. The resulting output was two narrow spectral lines that could each be tuned across the entire gain bandwidth of the system. Although this source has many potential applications, our intention is to use it for differential absorption lidar (DIAL) measurements and to drive THz-wave generation through difference frequency mixing in a nonlinear medium.