首先通过长脉冲激光与短脉冲之间比较引出皮秒激光技术,其次对皮秒激光技术的发展历程进行阐述,再次介绍了国内和国外的皮秒激光技术发展现状,从次叙述了基于SESAM被动锁模技术的皮秒激光脉冲形成的物理过程,包括非线性放大阶段、非线性吸收阶段和线性放大阶段,另外,介绍了皮秒激光加工技术的优点和应用,其中皮秒激光加工技术应用包括金属钻孔、划线、切割、表面结构化、表面清洗等等几个方面以及具体实例。最后通过比较纳秒、皮秒和飞秒三种激光技术的优劣势来表达对皮秒激光技术的未来展望。
Firstly, the picosecond laser technology is introduced by comparing the long pulse laser with the short pulse laser. Secondly, the development history of the picosecond laser technology is de-scribed. Thirdly, the development status of the domestic and foreign picosecond laser technology is introduced. Then, the physical process of picosecond laser pulse formation based on SESAM passive mode locking technology is described, including nonlinear amplification stage, nonlinear absorption stage and line. In addition, the advantages and applications of picosecond laser processing technology are introduced. The application of picosecond laser processing technology includes metal drilling, marking, cutting, surface structure, surface cleaning and so on. Finally, by comparing the advantages and disadvantages of nanosecond, picosecond and femtosecond laser technology, the future prospect of picosecond laser technology is expressed.
Firstly, the picosecond laser technology is introduced by comparing the long pulse laser with the short pulse laser. Secondly, the development history of the picosecond laser technology is described. Thirdly, the development status of the domestic and foreign picosecond laser technology is introduced. Then, the physical process of picosecond laser pulse formation based on SESAM passive mode locking technology is described, including nonlinear amplification stage, nonlinear absorption stage and line. In addition, the advantages and applications of picosecond laser processing technology are introduced. The application of picosecond laser processing technology includes metal drilling, marking, cutting, surface structure, surface cleaning and so on. Finally, by comparing the advantages and disadvantages of nanosecond, picosecond and femtosecond laser technology, the future prospect of picosecond laser technology is expressed.
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1. 引言
自1960年5月西奥多·哈罗德·梅曼(Theodore H. Maiman)点亮了第一束激光之后,激光技术在几十年间以惊人的速度迅速发展,被广泛应用于生产实践中,例如制造业、军事、医疗、通讯等方面。作为一项通用的、强有力的、最现代化的万能工具,激光在制造业领域占有重要地位,随着制造业的生产要求在不断提高,许多传统的加工技术已经无法满足加工需求,而激光的出现刚好解决了这一问题。在很久以前,人们就想到用激光对各种材料进行微加工 [1] [2],但所使用的激光脉宽长,且亮度低,所以导致的结果就是被加工的材料熔化并且持续蒸发。即使激光束的光斑小,但是对于被加工材料的热破坏较大,加工精度也随之受到影响,如图1所示。从图1中可以看出在长脉冲激光加工过程中,会产生喷射的熔融材料、表面残屑、重铸层以冲击波造成的表面波纹对相邻结构的破坏等。因此要想提高加工的质量,就必须得减少激光工作时所产生的热量,而超短脉冲就是最合适、最理想的工具,如图2表示的是长脉冲、短脉冲和超短脉冲激光加工效果对比图。从图2中可以分析出使用皮秒激光加工的效果最好,对材料产生的影响最小。当激光的脉冲宽度达到皮秒量级的时候——也就是皮秒激光,极高的功率密度与极短的相互作用时间使得激光束在工作时,不会给被加工材料带来热效应,所以也被称之为冷加工技术。
目前,世界上仅有几个国外的企业掌握着核心技术,他们主要来自于发达国家,包括德国的通快公司、美国的Coherent公司等,主导着全球皮秒激光市场的发展方向。以德国和美国的公司为例,德国的通快公司利用薄片激光放大技术实现了200 W的皮秒激光能量输出,而且光束质量非常好,受到广大企业和科研工作者的青睐,占据了激光加工的大部分市场。而美国的Coherent公司则利用基于主振荡功率放大系统的多级行波放大的方法,也将皮秒激光器的输出能量提高到了50 W [8]。