Qingming Lu

70% slope efficiency from an ultrafast laser-written Nd:GdVO4 channel waveguide laser.

We report high efficiency continuous wave laser oscillations at 1063.6 nm from an ultrafast laser written Nd(3+):GdVO4 channel waveguide under the 808 nm optical excitation. A record 17 mm·s(-1) writing speed was used while the low propagation loss of the waveguide (~0.5 dB·cm(-1)) enabled laser performance with a threshold pump power as low as 52 mW and a near to quantum defect limited laser slope efficiency of 70%.

Optical waveguides formed in Nd:YVO4 by MeV Si+ implantation

The planar waveguide has been fabricated in a Nd:YVO4 crystal by 3.0 MeV Si+ ion implantation at a dose of 1×1015 ions/cm2 at room temperature. The waveguide was characterized by the prism-coupling method. The dark modes are measured before and after the annealing at 240 °C for 60 min in air. The refractive index profile is reconstructed using reflectivity calculation method. It is found that relatively large positive change of ordinary refractive index happens in the guiding region, which is quite different from most of the observed ion-implanted waveguides. The TRIM’98 code is carried out to simulate the energy loss during the implantation in order to obtain a better understanding for the waveguide formation.

Growth, structure and thermal properties of Yb3+-doped NaGd(WO4)2 crystal

Yb3+ : NaGd(WO4)2 single crystal with dimensions O30 × 60 mm2 has been grown by the Czochralski method. XRPD experimental results show that the as-grown Yb3+ : NaGd(WO4)2 crystal belongs to the tetragonal system and the I41/a space group. The high crystalline quality of the as-grown Yb3+ : NaGd(WO4)2 crystals was confirmed by HRXRD. The effective segregation coefficient of the Yb element in Yb3+ : NaGd(WO4)2 crystal growth was measured to be 0.812 using the x-ray fluorescence method. Subsequently, the thermal properties were systematically studied by measuring the thermal expansion, specific heat and thermal diffusion coefficients. The density of the as-grown Yb3+ : NaGd(WO4)2 crystal at 22 °C was measured by using the buoyancy method with a resulting value of 7.143 g cm−3 and almost linearly decreases as the temperature increases due to the thermal expansion. Comparing the thermal properties of several tungstate crystals, we find that the Yb3+ : NaGd(WO4)2 crystal possesses relatively larger anisotropic thermal expansion and specific heat but smaller thermal conductivity than those of other tungstate crystals.

Low-loss planar and stripe waveguides in Nd3+-doped silicate glass produced by oxygen-ion implantation

We report on the fabrication and characterization of low-loss planar and stripe waveguides in a Nd3+-doped glass by 6MeV oxygen-ion implantation at a dose of 1×1015ions∕cm2. The dark mode spectroscopy of the planar waveguide was measured using a prism coupling arrangement. The refractive index profile of the planar waveguide was reconstructed from a code based on the reflectivity calculation method. The results indicate that a refractive index enhanced region as well as an optical barrier have been created after the ion beam processing. The near-field mode profiles of the stripe waveguide were obtained by an end-fire coupling arrangement, by which three quasitransverse electric modes were observed. After annealing, the propagation losses of the planar and stripe waveguides were reduced to be ∼0.5 and ∼1.8dB∕cm, respectively.

Anisotropic thermal properties of monoclinic Yb:KLu(WO4)2 crystals

Yb:KLu(WO4)2 (KLuW) crystals with large size and good optical quality have been grown by the top-seeded solution growth (TSSG) method. The melting point and specific heat, anisotropic thermal expansion and thermal conductivity have been measured. The Jackson factor α of a series of observed faces (hkl) on Yb:KLuW crystals have been calculated. In addition, the microhardness has also been measured. We find that the thermal expansion anisotropy of Yb:KLuW is weaker than KGd(WO4)2 (KGW) and KYb(WO4)2 (KYbW) and the thermal conductivity is up to 4.4Wm−1k−1 along [205] directions at 25°C, which is the greatest in their family.

Channel waveguide lasers in Nd:GGG crystals fabricated by femtosecond laser inscription

Buried channel waveguides have been fabricated in Nd:GGG crystals by using the femtosecond laser inscription. The waveguides are confined between two filaments with propagation losses of 2.0 dB/cm. Stable continuous wave laser oscillation at ~1061 nm has been demonstrated at room temperature. Under 808 nm optical excitation, a pump threshold of 29 mW and a slope efficiency of 25% have been obtained.

Terahertz parametric oscillator based on KTiOPO 4 crystal

KTiOPO₄ (KTP) crystal is used as the nonlinear medium in a surface-emitted terahertz-wave parametric oscillator for the first time. The oscillating Stokes beam propagates along the x axis of the KTP crystal, the pumping beam propagates with a small incident angle θ(ext) to the x axis, and the polarizations of the pumping beam, the Stokes beam, and the THz wave are along the z axis. When θ(ext) is changed from 1.250° to 6.000°, the THz wave is intermittently tuned from 3.17 to 3.44 THz, from 4.19 to 5.19 THz, and from 5.55 to 6.13 THz. The maximum output of the THz wave is 336 nJ, obtained at 5.72 THz with a pumping energy of 80 mJ. The two frequency gaps, from 3.44 to 4.19 THz and from 5.19 to 5.55 THz, are located in the vicinities of the A₁ modes of 134 and 178.7  cm⁻¹, which are strongly infrared absorbing.

Planar optical waveguides in β-BaB2O4 produced by oxygen ion implantation at low doses

The planar waveguides have been fabricated in z-cut β-BaB2O4 crystal by 2.2MeV O+ ion implantation at doses ranging from 5×1012 to 5×1014ions∕cm2 at room temperature. The waveguides were characterized by the prism-coupling method. Monomode, nonleaky planar waveguides at λ=633nm in β-BBO single crystals were fabricated at doses from 5×1012 to 2×1013ions∕cm2, and two mode and three mode waveguides were fabricated at doses from 4×1013 to 5×1014ions∕cm2, respectively. The refractive index profiles of the waveguides are reconstructed using reflectivity calculation method. The propagation loss of the measured ion implanted waveguide was about 1.6dB∕cm. It was found that positive changes of extraordinary refractive indices happened in the guiding regions, and such changes increased with the doses, which were different from most of the observed ion-implanted waveguides.

Ion-implanted waveguides in Nd3+-doped silicate glass and Er3+/Yb3+ co-doped phosphate glass

The data are presented on the waveguides formation in the Nd 3þ -doped silicate glass and Er 3þ /Yb 3þ co-doped phosphate glass by the implantations of He þ or Si þ ions, respectively. The prism-coupling method is used to measure the effective refractive indices of the waveguide dark modes. The refractive index profiles of the waveguides are reconstructed by using the reflectivity calculation method (RCM) and a comparison of such profiles among the different waveguides has been made. The reasons for the formation of the present waveguides are analyzed in a primary way. # 2002 Elsevier Science B.V. All rights reserved.

Femtosecond-Laser-Inscribed BiB3O6 Nonlinear Cladding Waveguide for Second-Harmonic Generation

We report on the fabrication of a nonlinear cladding waveguide in BiB3O6 crystal by using femtosecond laser inscription. The waveguide (with a nearly circular cross section of 150 µm diameter) shows good guiding properties in two transverse polarizations. The guided-wave second-harmonic generation (SHG) at 532 nm green light has been realized under CW and pulsed wave pump at 1064 nm, based on the Type I birefringent phase matching configuration. The conversion efficiencies for CW and pulsed green laser SHG are 0.083 and 25%, respectively.