Chenghui Huang

Yellow-light generation of 5.7 W by intracavity doubling self-Raman laser of YVO 4 /Nd:YVO 4 composite

A high-power 588 nm light produced by an intracavity frequency-doubling acousto-optic Q-switched self-frequency Raman laser is reported. A 20-mm-long YVO(4)/Nd:YVO(4) composite crystal and a 15-mm-long LiB(3)O(5) (LBO) with noncritical phase-matching (theta=90 degrees , phi=0 degrees ) cut were adopted for efficient self-Raman laser operation and second-harmonic generation, respectively. By the optimizing the focus position of incident pump light and Q-switch repetition rate, yellow light with 5.7 W average power was generated under the pump power of 23.5 W, corresponding to the overall diode-yellow conversion efficiency of 24.2% and slope efficiency of 32%. The pulse width is about 16 ns, and the pulse energy is up to 95 microJ.

Efficient second harmonic generation of double-end diffusion-bonded Nd:YVO4 self-Raman laser producing 7.9 W yellow light

A high power and efficient 588 nm yellow light is demonstrated through intracavity frequency doubling of an acousto-optic Q-switched self-frequency Raman laser. A 30-mm-length double-end diffusion-bonded Nd:YVO(4) crystal was utilized for efficient self-Raman laser operation by reducing the thermal effects and increasing the interaction length for the stimulated Raman scattering. A 15-mm-length LBO with non-critical phase matching (theta = 90 degrees, phi = 0 degrees) cut was adopted for efficient second-harmonic generation. The focus position of incident pump light and both the repetition rate and the duty cycle of the Q-switch have been optimized. At a repetition rate of 110 kHz and a duty cycle of 5%, the average power of 588 nm light is up to 7.93 W while the incident pump power is 26.5 W, corresponding to an overall diode-yellow conversion efficiency of 30% and a slope efficiency of 43%.

High-efficiency intracavity Nd:YVO 4 \KTA optical parametric oscillator with 3.6 W output power at 1.53 μm

An efficient intracavity KTA optical parametric oscillator (OPO) driven by diode-end-pumped acousto-optical Q-switched Nd:YVO(4) laser is demonstrated. The mode mismatch between fundamental cavity and OPO cavity caused by the thermal lens effect in Nd:YVO(4) crystal as the pump power increased was studied. To lessen mode mismatch, a thermal lens-like cavity mirror made of plane BK7 glass induced by idler absorption was introduced into the OPO cavity. Under a diode pump power of 20 W, a maximum 1535nm light output power of 3.6 W was achieved at the pulse repetition rate of 60 kHz, corresponding to a diode-to-signal conversion efficiency of 18%. This is the highest efficiency reported for eye-safe laser based on intracavity OPO.

Potential sodium D 2 resonance radiation generated by intra-cavity SHG of a c-cut Nd:YVO 4 self-Raman laser

Intra-cavity frequency doubling with 589 nm emission from a compact c-cut Nd:YVO4 crystal self-Raman laser was investigated. A 15-cm-length LBO with non-critical phase-matching cut (θ = 90°, ϕ = 0°) was used for efficient second-harmonic generation. At a pump power of 16.2 W and a pulse repetition frequency of 40 kHz, output power up to 2.15 W was achieved with a pulse width of 16 ns and a conversion efficiency of 13.3% with respect to the diode pump power. The center wavelength was measured to be 589.17 nm with a Half-Maximum-Full-Width of 0.2 nm, which was well in accordance with the sodium D2 resonance radiation.

Diode-side-pumped Nd:YAG laser at 1338 nm

In this Letter, a high-power diode-side-pumped Nd:YAG laser emitting at 1338 nm is described. The output characteristics of the laser using the different output couplers for both the cw mode and the Q-switched mode have been studied. With a pumping power of 555 W, the average output power decreases from 70 W at 50 kHz to 55 W (slope efficiency 21.2%, optical conversion efficiency 10%) at 5 kHz. The highest peak power is up to 73 kW with the pulse duration of 150 ns at the repetition rate of 5 kHz. When operated in cw mode, the output power of 100.5 W was achieved, corresponding with the optical slope efficiency of 36%.

Temperature dependence of electron redistribution in modulation-doped InAs/GaAs quantum dots

In this work we report the photoluminescence (PL) and interband absorption study of Si-modulation-doped multilayer InAs/GaAs quantum dots grown by molecular beam epitaxy (MBE) on (100) oriented GaAs substrates. Low-temperature PL shows a distinctive double-peak feature. Power-dependent PL and transmission electron microscopy (TEM) confirm that they stem from the ground states emission of islands of bimodal size distribution. Temperature-dependent PL study indicates that the family of small dots is ensemble effect dominated while the family of large dots is likely to be dominated by the intrinsic property of single quantum dots (QDs). The temperature-dependent PL and interband absorption measurements are discussed in terms of thermalized redistribution of the carriers among groups of QDs of different sizes in the ensemble

Diode-Side-Pumped Acoustooptic

In this paper, a diode-side-pumped acoustooptic Q-switched 1319-nm Nd:YAG laser is described. The output characteristics under the different repetition rates and output couplers have been studied. With a pumping power of 555 W, the average output power decreases from 94 W at 50 kHz to 71 W (slope efficiency 25.2%, optical conversion efficiency 12.8%) at 5 kHz. The highest peak power is up to 95 kW with the pulse duration of 150 ns at the repetition rate of 5 kHz.

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The isothermal decomposition of austenite into ferrite is investigated using a two-dimensional cellular automaton (CA) algorithm. This CA model provides a simple solution for the difficult moving boundary problem that governs the ferrite grain growth. In this model, the growth of ferrite grains is controlled by both the austenite–ferrite (γ–α) interface mobility and the carbon diffusion in the retained austenite. The competition between the γ–α interface dynamics and the carbon diffusion in the austenite results in a non-equilibrium γ–α interface condition. In order to predict the growth kinetics of ferrite grains, the carbon diffusion coupled with the γ–α interface dynamics is resolved numerically. The driving force for the γ–α interface mobility is calculated using a regular solute sub-lattice model. The kinetics of ferrite transformation predicted by this CA method is compared with that of a JMA model and experiments in the literature. The simulation provides an insight into the carbon diffusion in austenite and the microstructure evolution during transformation. Meanwhile, the results also show that the γ–α interface under the present non-equilibrium condition is numerically stable in two dimensions and the simulated morphology of the ferrite grains is an almost equiaxed polygon.

-switched 1319-nm Nd:YAG Laser

A finite element analysis was performed to study the strain induced transformation rolling process through which ultra-fine-grain steels were produced. Within the surface layer of the specimen, where ultra-fined grains were found, high strain and severe undercooling were found to coexist during hot deformation. It is proposed in this paper that the ultra-refinement was caused by the deformation of austenite in a severely undercooled state. To verify the grain refinement potential of severe undercooling thermomechanical treatment, hot compression experiments were done on a Gleeble1500 thermo-mechanical simulator. Severe undercooling was obtained by cooling the specimens at very high cooling rate before deformation. Metallographic observations showed that ultrafine grains could be obtained at a true strain of 0.9 provided that undercooling was higher than 200 K

A cellular automaton model for austenite to ferrite transformation in carbon steel under non-equilibrium interface conditions

The stable compact operation in the deep ultraviolet laser at 266 nm is reported from a diode-end-pumped acoustic-optic Q-switched Nd:YVO4/KTP/BBO laser. Fourth harmonic is generated by employing multiple reflections of 532 nm light for taking full advantage of the green beam. An ultraviolet laser at 266 nm with average power of 388.5 mW is obtained with a repetition-rate of 20 kHz, a pulse width of about 59.80 ns, and the corresponding optical to optical conversion efficiency of 11.9% from green to UV. High conversion efficiency and a circular spot of 266 nm laser beam have been achieved in an unfocused beam arrangement.