355 nm ultraviolet laser output based on a PPMgLN crystal.

This paper reports the method of generating a 355 nm ultraviolet (UV) quasicontinuous pulse laser by using two periodically poled Mg-doped lithium niobate (PPMgLN) crystals in a single-pass cascade. In the first PPMgLN crystal with a length of 20 mm and a first-order-poled period of 6.97 µm, the second-harmonic light of a 532 nm laser with 780 mW is generated from the 1064 nm laser with an average power of 2 W; After that, in the second PPMgLN crystal with a length of 15 mm and a third-order-poled period of 5.30 µm, the 532 nm laser generated was combined with the 1064 nm laser remaining through the first PPMgLN crystal to obtain a 355 nm UV laser with a maximum output average power of 20 mW, a repetition rate of 40 kHz, a pulse width of 49 ns, and a peak power of 10 W. Compared with existing reports, we have higher peak power and single pulse energy, which is an important application of the PPMgLN crystal. This paper will provide an important case for the realization of a 355 nm UV quasicontinuous or a continuous laser.

Broadband yellow-orange light generation based on a step-chirped PPMgLN ridge waveguide.

Yellow-orange lights, valuable in photodynamic therapies, spectroscopy, and optogenetics, are limited by the narrow bandwidth and bulky setup via the conventional Raman or optical parametric oscillation processes. Moreover, flatness in the broad-band spectrum is also important for the aforementioned applications with extended functions. In this paper, by carefully designing grating-periods of a step-chirped PPMgLN ridge waveguide for sum frequency generation (SFG), we report a compact broad-band yellow-orange light with bandwidth of 5.6 nm and an un-reported flatness (<1.5 dB). Correspondingly, the optical conversion efficiency is 232.08%/W, which is the best SFG efficiency for PPMgLN at the yellow-orange region, to the best of our knowledge. The results could also be adopted for other broad-band SFG process toward the vis-infrared region in an integrated structure.

Broadening of the sum-frequency phase-matching bandwidth by temperature gradient in MgO:PPLN.

We demonstrate bandwidth broadening in cascaded MgO-doped periodically poled lithium niobate (MgO:PPLN) crystals (Λ=10.3 µm) using the temperature-gradient technique. Up to 2.8 nm bandwidth at 600 nm spectral region is achieved using two 50 mm long cascaded MgO:PPLN crystals via sum frequency generation. This technique combines the merits of high conversion efficiency attributed to cascaded nonlinearity and the reconfigurability of temperature-gradient-induced chirp for broadening of the input wavelength acceptance range.

Electro-optic beam deflection based on a lithium niobate waveguide with microstructured serrated electrodes.

We report on electro-optic beam deflection using an annealed proton exchange waveguide in lithium niobate (LN) with microstructured serrated array electrodes. Due to the electro-optic effect of the LN material, the experimental results show that the beam deflection and modulation of the LN waveguide can be realized with relatively low voltages. The total length of the serrated prism array electrodes structure is ∼5 mm. With 20 V applied to the electrodes of 50, 100, and 150 µm wide waveguides, ∼1.28, ∼0.96, and ∼0.64 µm beam deflections were obtained, respectively, which are in accordance with theoretical simulation. This configuration can be potentially applied in optical beam scanning, high-speed switches, and optical beam smoothing technology.

Simultaneous Second-Harmonic, Sum-Frequency Generation and Stimulated Raman Scattering in MgO:PPLN.

In this study, simultaneous second-harmonic generation (SHG), sum frequency generation (SFG), and Raman conversion based on MgO-doped periodically poled lithium niobate (MgO:PPLN) for multi-wavelength generation is demonstrated. The approach used is based on a single MgO:PPLN crystal poled with a uniform period of 10.2 µm that phase matches SHG and SFG, simultaneously. Using a simplified double-pass geometry, up to 0.8 W of blue light at 487 nm is achieved by a frequency-doubling 974 nm laser diode pump, and 0.5 W of orange light at 598 nm is generated by frequency mixing 974 nm pump with C-band (1527⁻1565 nm) tunable laser source. At high pump powers of the 974 nm laser source, other unexpected peaks at 437, 536, 756, 815 and 1038 nm were observed, of which the 1038 nm line is due to Stimulated Raman Scattering within the MgO:PPLN crystal. The resulting multi-wavelength light source may find a wide range of applications in biomedicine and basic research.

Ultrabroadband tunable continuous-wave difference-frequency generation in periodically poled lithium niobate waveguides.

We report, for what is the first time to our knowledge, widely tunable mid-IR light generation over a range of greater than 1000 nm in the 4 microm region by employing a single quasi-phase-matched periodically poled niobate waveguide at room temperature. The waveguide we used was fabricated by annealed proton exchange based on periodically poled lithium niobate. A peak conversion efficiency of 10%/W and a linewidth as small as 37 MHz were achieved. The developed mid-IR light generator may find wide applications in trace gas detection of multiple atmospheric species and high-resolution spectroscopy.