Dazhi Lu

Self-frequency-doubled vibronic yellow Yb:YCOB laser at the wavelength of 570 nm

A watt-level self-frequency-doubled yellow laser at the 570 nm wavelength was realized by taking advantage of the vibronic emission of a Yb3+ doped calcium yttrium oxoborate (Yb:YCOB) crystal cut along the optimized direction out of the principal planes with the maximum effective nonlinear coefficient. Fluorescence spectroscopic properties of Yb:YCOB were studied, which showed that it had broad and anisotropic vibronic emission with a small peak at ∼1130  nm. By suppressing the electronic emission, the polarized vibronic Yb:YCOB radiation was realized with the fundamental wavelength shifting from 1130 nm to 1140 nm. By employing the self-frequency-doubling behavior of Yb:YCOB, the self-frequency-doubled yellow laser was achieved with a maximum output power of 1.08 W at 570 nm. This work provides an unprecedented and efficient way to generate yellow lasers with a compact microchip structure that may have promising applications in some regimes including medicine, entertainment, and scientific research.

Passively Q-switched ytterbium-doped ScBO3 laser with black phosphorus saturable absorber

Abstract. We demonstrate a passively Q-switched Yb3+-doped ScBO3 bulk laser using a black phosphorous (BP) saturable absorber, a two-dimensional semiconductor. The response spectra of BP show that it is suitable as a universal switcher in the spectral range from the visible to midinfrared band. Considering the saturable absorption properties of BP and emission properties of Yb3+-doped crystals, the passively Q-switched bulk laser pulses were realized with the Yb3+:ScBO3 crystal as a gain material and a fabricated BP sample as a Q-switcher. Because of the large energy storage capacity of Yb3+:ScBO3, the maximum output energy is obtained to be 1.4  μJ, which is comparable with the previous reported maximum energy of graphene Q-switched lasers. The obtained results identify the potential capability of BP as a pulse modulator in bulk lasers, and BP plays an increasingly important role in a wide range of its applications, including photonics and optoelectronics.

A naturally grown three-dimensional nonlinear photonic crystal

Nonlinear frequency conversion via three-dimensional(3D) quasi-phase matching (QPM) process is experimentally realized based on a Ba0.77Ca0.23TiO3 (BCT) crystal. The ferroelectric domains in BCT crystal are observed, and the results reveal that the antiparallel domains distribute in three dimensions and can provide 3D reciprocal lattice vectors for QPM processes. Broadband petal-like second-harmonic patterns are achieved, which are well consistent with the theoretical quasi-cubic model of 3Dnonlinearphotonic crystals. Our work not only promotes the development of QPM technique but also builds a platform for 3Dnonlinear optics and quantum optics.

Acentric langanite La 3 Ga 5.5 Nb 0.5 O 14 crystal: a new nonlinear crystal for the generation of mid-infrared parametric light

The mid-infrared spectral range extending from 2 to 6 μm is significant for scientific and technological applications. A promising nonlinear oxide crystal La3Ga5.5Nb0.5O14 (LGN) is proposed and fully characterized for the first time to our knowledge. The transparency range extends between 0.28 and 7.4 μm. The two principal refractive indices were measured and we found that the nonlinear coefficient d11 = 3.0 ± 0.1 pm/V at 0.532 μm. The simultaneous fit of data allowed us to refine the Sellmeier equations of LGN and to calculate the tuning curves for optical parametric generation (OPG) pumped at 1.064 μm. Calculations are consistent with recorded data and also show the generation of a supercontinuum between 1.5 and 3.5 μm when pumped at 0.98 μm by a Ti:Sapphire laser.

Exploration of Yb 3+ :ScBO 3 - a novel laser crystal in the rare-earth ion doped orthoborate system

Growth of optical-quality crystals with a borate anionic group and small-diameter cations is challenging. By compensating for the volatilization of boracic acid, an optical-quality Yb3+:ScBO3 laser crystal suitable for laser applications has been grown by the Czochralski method. The thermal and spectral properties of Yb3+:ScBO3 were experimentally and theoretically studied, including the thermal expansion, thermal diffusivity, specific heat, thermal conductivity, and the absorption and low-temperature emission spectra. The results indicate that this crystal exhibits a thermal conductivity that increases with temperature, and large energy storage properties that indicate promise for utilization in moderate power lasers. A continuous-wave Yb3+:ScBO3 crystal laser has, to the best of our knowledge, been demonstrated for the first time, with a maximum output power of 106 mW. All the results are indicative of a novel promising laser medium for applications in low and even moderate power lasers.

Phase-matching properties and refined Sellmeier equations of La3Ga55Nb05O14

We directly measured the phase-matching angles of second-harmonic generation and difference-frequency generation up to 6.5 µm in the Langanate crystal La3Ga5.5Nb0.5O14 (LGN). We also determined the nonlinear coefficient and damage threshold. We refined the Sellmeier equations of the ordinary and extraordinary principal refractive indices, and calculated the conditions of supercontinuum generation.

High repetition rates optically active langasite electro-optically Q-switched laser at 134 μm

An electro-optically Q-switched pulsed laser at 1.34 μm with a repetition rate of 100 kHz applying optically active langasite (La3Ga5SiO14) crystal has been reported. With Nd:YVO4 as laser crystal, the electro-optically Q-switched pulsed lasers were obtained with the maximum repetition rate of 100 kHz, maximum average output power of 2.42 W, and a minimum pulse width of 2.4 ns. Based on the theory of rate equations, the optimal pulse energy of the electro-optical Q-switching could be calculated. The experimental results have been found to be matched well with the theoretical calculations. To the best of our knowledge, this work presents the highest repetition rate and shortest pulse width which are achieved by an electric-optic LGS Q-switching at the wavelength of 1.34 μm, and it enriches the material categories for generating the high repetition rate pulsed laser.

Studies about relationships between the symmetries of ferroelectric crystal and frequency-doubled patterns

The broadband quasi-phase-matching process in Ca0.28Ba0.72Nb2O6 was demonstrated and the relationships between crystal symmetries and second-harmonic patterns were studied. Considering the light-matter interaction, the frequency-doubled photons were found to be trapped by a centripetal force.

Investigations on Yb 3+ :ScBO 3 - a novel laser crystal in rare-earth ions doped orthoborate systems

Optical-quality Yb3+:ScBO3 crystal has been grown by the Czochralski method. The thermal and spectral properties were studied. The continuous-wave Yb3+:ScBO3 crystal laser has been demonstrated which indicates its promising utilization in moderate-power lasers.