Dong Jingxing

Improved adhesion of diamond coating on cobalt-cemented tungsten carbide hardmetal by using pulsed-UV-laser substrate surface pretreatment

Abstract Pulsed-UV-laser surface ablation has been applied in substrate pretreatment in order to obtain good adhesion of diamond coating grown on cobalt-cemented tungsten carbide hardmetal. The dependence of diamond coating’s adhesion on different shots of pulsed-UV-laser substrate pretreatment has been studied experimentally. The results were compared with diamond coating deposited by using traditional acid-etching substrate pretreatment. It was shown that adhesion of diamond coating grown on tungsten carbide hardmetal has been greatly improved by using pulsed-UV-laser substrate pretreatment. The corresponding laser pretreatment condition for the optimal adhesion of diamond coatings was finally obtained. It has been demonstrated that pulsed-UV-laser substrate pretreatment should be a feasible and effective method for improving adhesion of diamond coating on cobalt-cemented tungsten carbide hardmetal. It is the characteristic surface morphology produced by pulsed-UV-laser surface ablation that subsequently results in this improved adhesion of diamond coating grown on tungsten carbide hardmetal. The number of laser shots being used in substrate pretreatment has a great influence to the adhesion of diamond coating deposited on tungsten carbide hardmetal. One should always apply proper number of laser shots in pulsed-UV-laser substrate pretreatment when seeking for the optimal adhesion of diamond coating on tungsten carbide hardmetal. In this work, the corresponding number of laser shots for the optimal adhesion of diamond coating has found to be 300 laser shots.

Beam quality improvement of laser diode array by using off-axis external cavity

A novel off-axis external cavity is designed for laser diode array to improve the beam quality. In this external cavity, a circle aperture with variable size is used as a spatial filter. The diameter of aperture is optimized to 1.2mm and the off-axis angle of external cavity is optimized at 2.6 deg. In the optimal case, the beam parameter product (BPP) of laser diode array is reduced to 121 mm.mrad from 1050 mm.mrad with external cavity optical efficiency of 81%.

A 115-W Ytterbium-Doped Fibre Laser

We report a highly efficient ytterbium-doped double-clad fibre laser, one-end pumped by a 975-nm diode stack source and generating up to 115.6 W of cw output power at 1.1 μm. The maximum optical-to-optical conversion efficiency with respect to the launched pump power is 79% at 65-W output power, and the overall slope efficiency is about 69%.

The Improved Power of the Central Lobe in the Beam Combination and High Power Output

In order to increase the power fraction of the central lobe in the coherent beam combination of lasers in an array, the effects of the distance factor of near-field distribution on far-field interference patterns are calculated and demonstrated experimentally. An improved beam array of interwoven distribution is demonstrated to enable the power in the central lobe to reach 41%. An optimized mirror array is carefully designed to obtain a high duty ratio, which is up to 53.3% at a high power level. By using these optimized methods and designs, the passive phase locking of eight Yb-doped fiber amplifiers with ring cavities are obtained, and a pleasing interference pattern with 87% visibility is observed. The maximum coherent output power of the system is up to 1066 W.

Controllable Dual-Wavelength Fiber Laser

We demonstrate a controllable dual-wavelength fiber laser which contains a master laser and a slave laser. The master laser is a kind of ring cavity laser which can be injected into by the slave laser. The output laser wavelength is controlled by injected power of the slave laser; both single- and dual-wavelength operation can be achieved. Under free running, the master laser generates 1064 nm laser output. Here the slave laser is a 1072 nm fiber laser. The 1064 nm and 1072 nm laser coexist in output spectrum for relatively low injected power. Dual-wavelength and power-ratio-tunable operation can be achieved. If the injected power of the slave laser is high enough, the 1064 nm laser is extinguished automatically and there is only 1072 nm laser output.

Generation of 1 ns excimer laser output pulse by direct wave clipping

In this article, a 1 ns excimer laser pulse was obtained successfully from an ultraviolet preionized XeCl laser using a direct wave-clipping technique with some improvements over the conventional scheme in consideration of obtaining more suitable discharge and steeper front edge of original light pulse. The effects of laser operation stability and optical setup of the experiment scheme on output characteristics are discussed.

Line-width reduction of a laser diode array using an external cavity with two feedback mirrors

A novel Littman-Metcalf external cavity laser diode array with two feedback mirrors is introduced. The line-width broadening effect caused by smile can be reduced by the novel external cavity. At the drive current of 16A, the line-width is narrowed to 0.1nm from free-running width of 1.6nm with output efficiency of 84%.

High power two-stage single frequency PM fiber amplifier

We demonstrate a two-stage single frequency polarization maintaining Yb-doped fiber Amplifier at 1064nm. The gain is 7dB and 17.6dB for the first and the second fiber amplifier. The output power is 17.3W with 62.8% slope efficiency for second fiber amplifier and the polarization extinction ratio is better than 24.3 dB.

The improvement of output pulse shape in nanosecond pulse fiber amplifier

The change of pulse shape in a MOFPA system was experimentally demonstrated. Through optimized the pulse shape, the amplifier can provide 59-W 1064 nm laser with pulse duration of 22.7ns at 50 kHz repetition rate.