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B a M g F 4 is a ferroelectric nonlinear crystal with a very wide transparency window ranging from 125 nm to 13 µ m of the wavelength. Therefore, it is a candidate material to generate ultraviolet or deep ultraviolet laser, which is very important in lithography, semiconductor manufacturing, and advanced instrument development. Here, the second-order birefringence phase-matching processes of the B a M g F 4 crystal were studied, including second-harmonic generation (SHG) and sum-frequency generation (SFG). In the experiments, we measured the phase-matching angle, nonlinear frequency conversion efficiency, and angle bandwidth of SHG and SFG processes of B a M g F 4 crystal, which are in well agreement with the theoretical calculations. This study may promote the research of nonlinear optical process of B a M g F 4 crystal and also the further development of all-solid-state vacuum ultraviolet lasers.

A bulk electro-optic (EO) modulator based on the ultrahigh-order guided modes, which are excited in a symmetrical metal-cladding waveguide (SMCW), has been exploited. This kind of mode in a SMCW has high sensitivity to phase shift by changing the refractive index of the guiding layer. Compared with phase modulation via the bulk EO modulator without a waveguide, the applied half-wave voltage is reduced for one magnitude. This work may have practical applications in optical information processes.

We theoretically study second-harmonic generation in two-dimensional nonlinear photonic crystals and obtain a unified expression that combines nonlinear Raman-Nath diffraction, Čerenkov-type second-harmonic generation, and nonlinear Bragg diffraction. The analytical solution is deduced, and the theoretical result coincides well with the nonlinear Raman-Nath, nonlinear Čerenkov, and nonlinear Bragg diffraction phase-matching conditions. This method has potential applications in second-harmonic generation of more complicated two-dimensional and even three-dimensional nonlinear photonic crystals.

The nonlinear refraction and nonlinear absorption phenomena are investigated in BaMgF(4) single crystal using the Z-scan technique in the ultraviolet region with a pulsed laser at 400 nm with 1 ps pulse duration. The remarkable nonlinear absorption behavior is identified to be three-photon absorption under the experimental conditions. In addition, both nonlinear refraction and nonlinear absorption have relatively large values and possess small anisotropy along three different crystallographic axes. The large values of nonlinear refractive index are demonstrated through the self-phase modulation effect.