Laser Beam Shaping And Using It In The Femtosecond Laser Micromachining

Owing to the short pulse, heavy peak power, small heat-affected zone and high resolution, femtosecond laser is different from long pulse laser. For these reasons femtosecond laser micromachining with great vitality has been noticed and studied in recent years. However in the process of micromachining, because of the inhomogeneous spot energy, the material interaction made by femtosecond laser is distinguishing, which greatly affects the application prospect of this technology. Beam shaping technology can change the optical field distribution in the time domain and frequency domain, which could get the uniform energy distribution. So this technology has very important application. Comparing with all other techniques, aspheric lens shaping is an effective method with the advantages of high energy utilization and high laser-induced damage threshold. So it is very suitable for femtosecond laser micromachining system. However the past most work focused on designing and optimizing lager beam shaping system. The system with focusing function has been studied little. This paper devise the aspheric system with focusing function and make use of it to experiment. The main contents are classified as follows.1. Analyzing the common Gauss and flat top beam model. Discussing the transfer characteristic of the flat top beam in the near field and far field, analyzing the logic of the function factor influence the intensity distribution, and simulating the relationship between output efficiency and beam uniformity.2. Discussing the design method of aspheric plastic system. Analyzing and summarizing the influence of parameters of Kepler and Galileo optical structure. By the method of least square method the best parameters of optical system structure has been calculated. Analyzing the principle deviation, manufacturing deviation and application deviation of the optical system. Meanwhile the tolerance range has been reckoned. According to the designing result the experimental platform is built. The non focus and the focus optical system are contrasted, and the minimum diameter of the flat top beam is 60μm.3. Building a femtosecond laser micromachining system and using this system to process the Titanium, Titanium alloy and sapphire. Contrasting the processing results of the Gauss beam and flat top beam and analyzing the spot energy distribution effect on the machining result. The result show that, the thermal effect of femtosecond laser micro-machining process is critical factors which affect the quality of the processing. The flat top beam result is better than the Gauss beam under the same condition.