An optical system is designed to shape the rectangular beam which emitted by direct high power laser diode stack for laser material processing. Beam parameter product theory and inverted Kepler telescope system principle are applied to analyze and design the optical system, the fast and slow axis beams of LD stack are focused in same focal plane. Firstly, two LD stacks with different wavelength are collimated by micro-lens array respectively. Then they are combined by dichroic beam splitter. Because of the divergence angle in slow axis direction is still big, the inverted Kepler telescope system is applied to expand and collimate the slow axis beam. Finally, the fast and slow axis beams are focused simultaneously. The whole optical path is simulated by ZEMAX software in the non-sequence mode and the simulated focused spot size and optical power density is obtained after ray tracing. Based on the theoretical calculation and software simulation, we perform the experiment and obtain a focused spot whose size is 2.0mm×5.0mm with 300mm focal length and 5 kilowatts power. The optical power density can reach to dozens of thousands of watts level. We discuss the influence factors of the focused spot size, and analyze the merit and demerit of the optical system. We also point out the improving orientation in the future. The laser beam after shaping by this optical system can be directly applied to laser cladding because of its long focal length and high optical power density.
In laser sintering we adopt the method of Nd: YAG frequency doubling to acquire short wave laser in order to obtain fine focus. The paper describes and discusses the method as well as the beam quality of the laser. Based on experiments and theories, we studied frequency doubling in a KTP crystal on Nd:YAG laser by the resonant external ring cavity. The Nd:YAG laser average power is 50w with Q-switch and its frequency is 1005Hz. In the experiment the wavelength of 0.532μm green light output was obtained with 31.4% light conversion efficiency when 1.064μm input average power is 35w. In the green light the proportion of TEM00 model is about 95%. The method is proved to be an effective way to solve the problem of how to get a mini-focus. It is especially useful in the application of laser rapid prototyping. The experimental results for the characteristics of ring cavity frequency doubling were analyzed. The two lasers of 1.064μm and 0.532μm on the beam quality were compared in this paper. The thesis provides the pictures of beam focuses tested with CCD and compares some experimental results with those pictures. A theory of the ring cavity frequency doubling has been put forward in this paper. The sintering effect of the 0.532μm laser was showed in contrast with the 1.064μm laser. The experimental results show that the short wave laser is better for the micro fabrication.
Many factors influence laser cutting quality. In this paper, the influence of laser head movement on 3D laser cutting is investigated. Except normal movement which laser head is vertical to work piece surface, three types of movement defined in 3D laser cutting are considered. Experimental design method is used to analyse cutting result. In order to quantitatively describe the relationship between cutting quality and cutting parameters, artificial neural network (ANN) has been setup. The quality marks system is used to evaluate cutting result. The test shows the calculated quality points by ANN is very similar with actual cutting result. The laser head forward movement is better than the others. The ANN is very useful to optimize cutting parameters, predict cutting result and deduce new information.
As laser microfabrication develops fast more and more micro parts of MEMS are produced with laser micro processing technology. Excimer laser ablation is a versatile tool for the micro machining of various materials. Excimer laser materials processing, which is performed in most cases using a mask projection system forms a 3D shape by ablation material. Recently a large number of articles about polymer ablation with excimer lasers have appeared. However the powder material especially metallic powder is paid little attention in excimer laser micro machining. In this paper several types of powder material are investigated in excimer laser ablation. The ablation rate of different powder materials with various fluence ranges, wavelengths, and pulse lengths are studied in experiment. The parameters of excimer laser were optimized to fabricate a micro part. The diameter of about 100 micron gear made of nano powder was finally produced with a mask project system using nanopowder. This method is more efficient than laser writing with a focal spot.
Selective laser sintering (SLS) is a process that uses a rastering laser to sinter powder particles into a computer defined shape. In order to fabricate micro part with laser sintering the laser beam spot should be focused smaller, on the other hand the size of sintered powder particles should be smaller too. Therefore Nd:YAG laser doubling frequency is used to obtain mini-focus. Based on theories of nonlinear and resonant cavity, an equipment which perform frequency doubling on YAG laser(1.06μm) by the external resonant ring cavity has been designed. With the equipment the wave length of 0.532μm green light was output. The focused laser spot of 15μm diameter was obtained with 10W power. Meanwhile the micron metal powder was used in selective laser micro sintering (SLMS). The behavior of laser sintering different metal powder was investigated. Finally the micro Chinese characters which is small as a tip of match made with laser selective micro sintering micron metal powder are shown.
The laser micro-fabrication technology for micromachine is a noticeable research direction in micro-machine manufacture. In this paper several laser micro-fabrication technologies have been introduced. They are laser mask project lithograph, focus laser beam etching, selective laser sintering rapid fabrication and laser direct deposited fused powder. Authors also introduce the micro gears made with excimer laser mask exposure lithograph in PMMA and the micro Chinese character which is as small as a tip of match made with powder laser sintering technology. Furthermore authors propose another way to make micro-part which use fiber laser or disk laser combined with nano powder.