Table 1.

Fabrication techniques of diffractive micro/nanostructures on IR materials.

Fabrication Technique Types	Fabrication Techniques	Limitations
Mechanical fabrication	Ultra-precision diamond cutting; diamond milling, fast tool servo (FTS), slow tool servo (STS), and vibration-assisted cutting	The height variation of the generated hybrid IR surfaces that is achievable is limited due to the adoption of very small feed rates and depths of cuts (FTS/STS). There is a restriction to the highest attainable periodicity of the secondary diffractive micro/nanostructures (FTS/STS).
	Ultrasonic vibration-assisted diamond cutting	Only suitable for planar surfaces. Difficult to generate hybrid structures with a freeform primary surface.
Non-mechanical fabrication	Electron beam lithography, laser ablation, focused ion beam	Restriction to planar substrates. They cannot generate concave/convex surfaces with a shorter radius of curvature.
	Etching (laser-assisted and chemical etching)	Facility requirements are expensive. Difficulty of generating complex secondary structures.
	Femtosecond laser polymerisation	Restriction to low-efficiency and photocurable polymer materials.
Hybrid (Mechanical and non-mechanical)	Ultra-precision machining and picosecond laser ablation	Introduction of unnecessary machining errors. Efficiency is relatively low, and it is relatively costly.