激光直写制备衍射光学元件的研究及应用

衍射光学元件作为一种典型的微光学元件，其体积小、质量轻、设计自由度多、成像质量良好，在光学成像、光学数据存储、激光技术、生物医学等领域具有广阔的应用前景。随着现代光学系统的不断发展，对衍射光学元件的加工效率和制备精度提出了更高的要求。激光直写技术凭借加工精度高、工艺简单、灵活性好等优势，成为制备高精密仪器中关键光学元件所必需的一种加工方式。针对不同的加工需求，开发了多种激光直写系统，并在应用过程中不断地改进升级。另外，突破衍射极限的飞秒激光微纳结构制造技术，能够获得更高的加工精度和更好的分辨率，为微光学元件的制备提供了新的方法。首先介绍了激光直写技术的特点；其次综述了衍射光学元件直写加工技术的研究进展，包括直写技术的影响因素、激光直写系统和多光束加工技术；接着介绍了衍射光学元件的典型应用，如红外成像、色差校正、光束整形、图像显示；最后，对激光直写技术制备衍射光学元件存在的问题和未来发展趋势做出了总结。

Research and application of diffractive optical element fabricated by laser direct writing

  Significance   Micro-optics theory is a new discipline for the study of the design and manufacturing of micron-sized and nano-sized optical components, as well as the use of such components to achieve the theory and technology development of light waves. As a research field of optics, diffractive optics is based on the diffraction principle of light waves developed microoptics. Diffractive optical technology is of great significance in realizing lightweight, miniaturization, integration, high efficiency and low cost of optoelectronic systems, and the development of diffractive optical technology has also become one of the important ways to develop modern optical systems. As a typical micro-optical element, diffractive optical elements have broad application prospects in industrial and civil fields such as optical imaging, laser technology, and biomedicine due to their small size, light weight, multiple degrees of design freedom and good imaging quality. The processing methods of optical element can be summarized into two types of mechanical processing and optical processing, both of which have their own advantages and disadvantages. The advent of laser provides a new idea for the preparation of diffractive optical elements. Laser processing is a non-contact wear-free technology with high precision and high flexibility, which can process complex contours and has the characteristic of environmental friendliness and simple production process, so the study of laser processing technology in the application of diffractive optical elements is of great significance.  Progress   With the continuous development of modern optical systems, higher requirements are put forward for the processing efficiency and preparation accuracy of diffractive optical elements. Laser direct writing technology does not need mask plate in the process of preparing diffractive optical elements, simplifies the steps, shortens the production cycle (Fig.1(a)). There are many factors affecting the preparation quality of diffractive optical elements, the article summarizes the main factors affecting the surface quality of diffractive optical elements (Fig.1(b)), and explains the influence of focusing system (Fig.2), laser energy (Fig.3) and scanning speed on the preparation of diffractive optical elements, which is very important for improving the preparation accuracy and surface quality of optical components. Different types of laser direct writing systems should also be considered in the preparation of diffractive optical element with different structures (Tab.1). From the aspects of process and system, the research progress of femtosecond laser direct writing system based on Cartesian coordinate system and polar coordinate system in processing diffractive optical element is discussed (Fig.4, Fig.6). Besides, in order to solve the problems of low energy utilization and poor processing efficiency in the process of laser preparation of diffractive optical element, a multi-beam parallel processing method based on laser direct writing technology is proposed (Fig.7). Diffractive optical elements have a variety of functions in optical systems due to their unique characteristics, and the article summarizes the typical applications of diffractive optical elements, such as infrared imaging (Fig.8), chromatic aberration correction, beam shaping, laser processing (Fig.9), image display, etc.  Conclusions and Prospects   In the field of optics, the development of micro-optics theory technology continues to promote the advancement of diffractive optics theory. The application of diffractive optical element has also been expanded in more fields. As a high-precision, programmable, short cycle and flexible processing method, laser direct writing technology has incomparable advantages in the preparation of diffractive optical element. But in the actual processing process, there are problems of limited processing materials, insufficient utilization of laser energy, and the complexity of the system caused by the alignment mechanism in the preparation of curved element, so the research on expanding materials, simplifying equipment, optimizing processes and seeking applications is a continuous and important topic.