Laser interference lithography (LIL) is a technique that allows for the simple, flexible, and rapid fabrication of high-resolution periodic structures over large areas without the use of masks. Different interference conditions can produce a wide range of light fields. When an LIL system is used to expose the substrate, a variety of periodic textured structures, such as periodic nanoparticles, dot arrays, hole arrays, and stripes, can be produced. The LIL technique can be used not only on flat substrates, but also on curved or partially curved substrates, taking advantage of the large depth of focus.
Nature is full of strange creatures, and many people have the impression that certain unique micro/nanosurfaces in nature are non-regular structures, but this is not the case 
. For example, the beautiful seashells, the wings of butterflies, the feathers of birds, the scales of pangolins, and the epidermis of sharks are all periodic-ordered structures 
. Furthermore, it is these microscopic periodic-ordered structures that give them various macroscopic properties such as wettability, wind/water resistance reduction, friction reduction, reflection reduction, and different structural colors.
As these regular surfaces are studied more thoroughly, it has been found that objects work better when these structures are “imitated” in a variety of ways on the surfaces 
. In recent decades, periodic regular structures have received increasing attention in many fields, and the study of these rules has become increasingly sophisticated. For example, researchers have studied wettability, and people prepare certain specific surface structures that can achieve the phenomenon of water flowing to high places 
. Some swimmers wear special shark suits and their speeds improve considerably 
. There are so many examples of these periodic regular structures benefiting human life. It is possible that a random object that people own contains a micro/nano-periodic structure that was designed by researchers.
Currently, as many as dozens of methods are used to produce periodic regular structures. From the broad categories, they can be divided into mechanical, optical, and chemical methods 
. Mechanical methods include scribing, EDM, nanoimprinting, water flow, etc.; chemical methods include electrochemical, hydrothermal, CVD deposition, etc.; and optical methods include femtosecond lasers, direct laser scanning, laser interference lithography (LIL), etc. However, these techniques have limitations in terms of low yield, small patterning area, and/or high equipment, and tooling cost. In contrast, LIL works on large areas at a low cost 
. Periodic structures are of interest for their inherent merits in functional applications such as diffraction modulation, controllable wettability, and reflection reduction, as well as for their different structural colors 
. There are many techniques capable of fabricating periodic structures, among which the LIL technique has incomparable advantages for the fabrication of periodically large-area patterned structures 
LIL is an advanced micro- and/or nanoprocessing technique that can be used to produce high-resolution micro- and/or nanostructures and devices 
. LIL uses the interference property of light to realize multiple coherent laser beams that meet on the substrate surface to form a bright and dark interference region with periodic light intensity distribution. The traditional lithography process is to expose the sample and transfer the pattern to the substrate surface through processes, such as development, etching, or coating, to form a patterned substrate. The periodic intensity distributions in the interference region are ‘recorded’ on the substrate, so LIL is a maskless optical exposure technique that avoids the use of mask plates and reduces the cost of lithography. LIL can produce large-area, high-resolution periodic patterns at a low cost, while the exposure process is simple and the pattern period can be flexibly changed 
. LIL can produce patterns not only on flat substrates, but also on curved or partially curved substrates using its large depth of focus.
2. Laser Interference Lithography
2.1. Types of Laser Interference Lithography
Laser interference lithography can be classified into various forms. According to the number of beams of interference, LIL can be divided into double-beam, triple-beam, quadruple-beam, quintuple-beam, and other multi-beam interference lithography 
; by the number of exposures, LIL can be divided into single-exposure lithography and multi-exposure lithography 
. Other lithography systems currently have to shorten the wavelength and sacrifice the depth of focus in order to pursue high resolution. Ion beam lithography and electron beam lithography have sufficient resolution, but their slow fabrication process limits their application in high-volume manufacturing. LIL is a fine graphics processing technique with a low cost, simple system, and high resolution. It has great advantages and a key position in preparing array structures. Its system is inexpensive, does not require complex optical components, it also has expensive imaging lenses and is capable of preparing graphics in large areas without the depth-of-focus limitation. It has a high resolution and does not require masks, making it a promising lithography technique at present.
LIL exploits the interference properties of light to realize multiple coherent laser beams that meet on the substrate surface to form bright and dark interference regions. The intensity distributions in interference regions are characterized by periodicity 
. LIL can produce controlled periodic or quasi-periodic structures on nano- and microscales, and fine periodic array structures can be fabricated under the strict control of the process and exposure dose 
Micro/nanostructures with different feature sizes are obtained through LIL. The interference of three laser beams is considered as the superposition of their electric field vectors. It can be expressed as 
is the amplitude of the electric field vector and
is the unit polarization vector.
is the wave number (
is the unit propagation vector in the wave propagating direction,
is the position vector,
is the phase constant, and
is the frequency. A flexible LIL system can select the parameters and obtain the designed interference pattern.
The interference intensity is expressed as 
2.2. Influence of the Process Parameters for Laser Interference Lithography
Laser interferometric lithography produces controllable periodic or quasi-periodic structures from nanoscale to microscale, producing fine periodic array structures with a tightly controlled process and exposure dose 
. Several factors determine the interference pattern and related parameters:
The number of laser beams producing different micro- and nanoarray structures;
The incident angle preparing the grating structure of different periods;
The azimuth angle producing different morphology arrays;
The energy of the laser determining the depth of the structure; and
The polarization state determining the pattern profile.
The basic principle of laser interference lithography is to combine two or more laser beams that meet the interference conditions according to the interference principle of light and change the exposure time, phase angle, incident angle, and other parameters that can obtain different periodic pattern arrays such as stripe array, dot array, and dimple (hole) array.