Xihong Fu

CW 50W/M2 = 10.9 diode laser source by spectral beam combining based on a transmission grating

An external cavity structure based on the -1st transmission grating is introduced to spectral beam combining a 970 nm diode laser bar. A CW output power of 50.8 W, an electro-optical conversion efficiency of 45%, a spectral beam combining efficiency of 90.2% and a holistic M(2) value of 10.9 are achieved. This shows a way for a diode laser source with several KW power and diffraction-limited beam quality at the same time.

Orthogonally polarized dual-wavelength Nd:YAlO(3) laser at 1341 and 1339 nm and sum-frequency mixing for an emission at 670 nm.

We report a diode-pumped continuous wave (cw) orthogonally polarized dual-wavelength laser at 1339 and 1341 nm with a single b-cut Nd:YAlO(3) (Nd:YAP) crystal. By adjusting the tilt angle of the uncoated glass plate inserted in the laser cavity, we can control the cavity losses of two polarized directions. The output wavelengths are 1339 nm in a-axis polarization and 1341 nm in c-axis polarization, respectively, which are orthogonal to each other. At an incident pump power of 17.3 W, the cw output power obtained at 1339 and 1341 nm is 1.6 and 2.3 W, respectively. Furthermore, intracavity sum-frequency mixing at 1339 and 1341 nm was then realized in a KTiOPO(4) (KTP) crystal to reach the red range. To our knowledge, this is the first work realizing an orthogonally polarized dual-wavelength Nd:YAP laser based on the (4)F(3/2-)-(4)I(13/2) transition. Such a dual-wavelength laser would be especially valuable as a compact laser source to generate terahertz emission because the frequency difference between 1339 and 1341 nm is about 0.9 THz.

Quasi-three-level neodymium-doped yttrium aluminum garnet laser emitting at 885 nm

We present a diode-pumped quasi-three-level neodymium-doped yttrium aluminum garnet (Nd:YAG) laser at 885 nm, based on the 4F3/2-4I9/2 transition, generally used for a 946 nm emission. Combined with polarization components (Nd:YAG), the electro-optical crystal KH2PO4 (KDP) formed a Lyot filter in the cavity and compressed the available gain bandwidth. With an incident pump power of 9.2 W, a 714 mW continuous-wave (CW) output at 885 nm was achieved, and the optical-to-optical efficiency was 7.8%. With an adjustable voltage applied to the KDP crystal, the laser wavelength could be tuned from 885 nm to 884 nm. A simultaneous dual-wavelength Nd:YAG laser at 885 nm and 884 nm was also realized by adjusting the free spectral range of the Lyot filter. To our knowledge, it is the first study that has realized the tuning between the 884 and 885 nm lines and the simultaneous dual-wavelength CW laser operation at 885 nm and 884 nm.

Giant Kerr nonlinearity via tunneling induced double dark resonances in triangular quantum dot molecules

A scheme for giant Kerr nonlinearity via tunneling in triangular triple quantum dot molecules is proposed. In such a system, the linear absorption and the Kerr nonlinearity depend critically on the energy splitting of the excited states and the tunneling intensity. With proper parameters, giant Kerr nonlinearity accompanied by vanishing absorption can be realized. The enhancement of Kerr nonlinearity is attributed to the interacting double dark resonances induced by the tunneling between the quantum dots, requiring no extra coupling laser fields.

Diode-pumped orthogonally polarized Nd:LuVO 4 lasers based on the 4 F 3/2 – 4 I 11/2 transition

A diode-pumped simultaneous orthogonally polarized continuous-wave (cw) dual-wavelength Nd:LuVO4 laser based on the F-4(3/2) - I-4(11/2) transition is experimentally demonstrated. A theoretical analysis has been introduced to determine the threshold conditions for simultaneous orthogonally polarized dual-wavelength laser. Using a polarization beam splitter included resonant cavity in the experiments, simultaneous orthogonal polarized dual-wavelength Nd:LuVO4 laser operation was realized at two close wavelengths near 1060-1070 nm. To our knowledge, this is the first work of realizing simultaneous dual-wavelength Nd:LuVO4 laser operation near 1060-1070 nm

Fine wavelength control in 1.3 μm Nd:YAG lasers by electro-optical crystal lens

A diode-pumped tunable and multi-wavelength continuous-wave Nd:YAG laser based on the 4F3/2−4I13/2 transition has been demonstrated for the first time. The combination of the glass plane positioned at the Brewster angle and the electro-optical crystal KH2PO4 (KDP) lens formed a Lyot filter in the cavity and compressed the available gain bandwidth. With an adjustable voltage applied to the KDP crystal lens, the laser wavelength could be tuned from 1333.8 to 1338.2 nm. Moreover, we can also realize cw dual-wavelength and triple-wavelength lasers with smaller wavelength separation by adjusting the free spectral range of the Lyot filter.

Design and analysis of high-temperature operating 795?nm VCSELs for chip-scale atomic clocks

We propose a new structure design and analysis of high-temperature (> 350 K) operating 795 nm vertical-cavity surface-emitting lasers (VCSELs) for Rb-87 based chip-scale atomic clocks (CSACs). Compositions and thicknesses of the InAlGaAs/AlGaAs multiple quantum wells (MQWs) are optimized for high optical gain at elevated temperatures. The temperature sensitivity of the threshold current is estimated by calculating the temperature dependence of the cavity-mode gain. A self-consistent VCSEL model based on quasi-3D finite element analysis is employed to investigate the temperature distribution and output of the proposed structure. An output of 1 mW with a 3 dB bandwidth of 6 GHz is obtained from a 3 mu m aperture VCSEL under 2.4 mA current at temperature higher than 340 K. These findings indicate that high-gain QWs and gain-offset consideration are especially crucial to make high-performance VCSELs at elevated temperatures.

980-nm High-Power Low-Divergence VCSELs Achieved by Optimization of Current Density Distribution

In this paper, we report the design and fabrication of 980-nm vertical-cavity surface-emitting lasers and arrays that provide high output power and low divergence angle without any additional collimating optics. The influence of the structure of the contact on the current density distribution inside the active region was analyzed using the 3-D finite-element method. Uniform current distribution is achieved by optimizing the diameter of the p-contact, and the consequent improvement in beam divergence and thermal behavior is shown. A low divergence angle of 5.4° is obtained for a single device with continuous-wave (CW) power of 1.46 W at room temperature. The 8 × 8 array shows a divergence angle of 10.2° at 4 A with a CW power of 1.95 W. In addition, the measured results were compared with the results from devices without optimization of current density distribution.

Effect of focus position and shear stresses on the crack sectional shape in semiconductor laser linear cutting glass

In laser-induced thermal-crack propagation, thermal stresses control the crack propagation mode and the quality of the crack surface. In this article, the 1064-nm semiconductor laser as a volumetric heat source is used for symmetry and asymmetry cutting glass. One of the problems in laser asymmetry linear cutting glass with laser-induced thermal-crack propagation is the quality of the crack surface which gets worse than that in symmetry cutting. This study lays great emphasis on analyzing the effect of the focus position and shear stresses on the crack sectional shape in semiconductor laser asymmetry linear cutting glass. This article indicates the volumetric heat flux formula, which simulates the temperature distribution from the material above or below the focal point. The heat source should be positioned above the focal point. Optical microscope photographs of the crack surface and sectional shape are obtained to examine the surface quality which is explained from the results of the stress fields using the extended finite element method simulation. In asymmetry cutting, shear stress is parallel to the crack surface and perpendicular to the cutting direction, which makes the crack surface smooth but uneven.

A diode-pumped Nd:YAlO3 dual-wavelength yellow light source

We present what is, to the best of our knowledge, the first diode-pumped Nd:YAlO3 (Nd:YAP) continuous-wave (cw) dual-wavelength yellow laser at 593 nm and 598 nm, based on sum-frequency generation between 1064 and 1339 nm in a-axis polarization using LBO crystal and between 1079 and 1341 nm in c-axis polarization using PPKTP crystal, respectively. At an incident pump power of 17.3 W, the maximum output power obtained at 593 nm and 598 nm is 0.18 W and 1.86 W, respectively. The laser experiment shows that Nd:YAP crystal can be used for an efficient diode-pumped dual-wavelength yellow laser system. (Some figures may appear in colour only in the online journal)