Shanghai Institute of Optics and Mechanics has made progress in preparing optical metamaterials by femtosecond laser

Recently, the Thin Film Optics Laboratory of Shanghai Institute of Optics and Precision Machinery, Chinese Academy of Sciences has made progress in the preparation of negative refractive optical metamaterials by femtosecond laser, and the relevant research achievements were published on Nanomaterials under the title of "Fast Fabric of Fishnet Optical Metamaterial Based on Femtosecond Laser Induced Stress Break Technique".

Optical metamaterials have broad application prospects in many fields. Optical hypersurface can realize the manipulation and modulation of light and electromagnetic wave by using the phase mutation of light on the subwavelength surface. Femtosecond laser processing technology has the advantages of fast processing speed, no mask required, processing at room temperature, processing transparent and superhard materials, low cost, etc. It can achieve rapid preparation of optical band metamaterials and super surfaces.

The researchers used femtosecond laser direct writing to rapidly prepare a negative refractive metamaterial with circular fishing net structure, and revealed that there are two interaction mechanisms of femtosecond laser and metal medium metal fishing net structure, namely, thermal melting and stress destruction. Among them, the thermal melting process dominates the interaction between femtosecond laser and metal, causing the upper and lower metal to stick together, making magnetic resonance impossible. The laser induced stress destruction process dominates the interaction process between femtosecond laser and medium, which can inhibit the thermal diffusion and thermal damage in the fishing net structure, separate the upper and lower metals, and enable magnetic resonance to occur. Using the advantage of stress destruction, the subwavelength periodic hole arrays were fabricated in metal dielectric metal films by femtosecond laser direct writing back processing technology. The transmission and reflection spectra of the fishing net structure hypersurface show that the fishing net structure prepared by femtosecond laser direct writing technology can generate magnetic resonance, and the femtosecond laser induced stress destruction technology can be used to rapidly prepare optical hypersurface.

Based on the characteristics of back ablation, high numerical aperture and super Gaussian beam, the optical metamaterial of fishing net constructed by femtosecond laser induced stress fracture technology has a resolution of 500 nm and a processing speed of 100 units/second, respectively. The measurement results of spectrophotometer can prove that magnetic resonance has been found in fishing net nanostructures. The theoretical refractive index of the metamaterial on the glass substrate reaches - 0.12 at 3225 nm. This work confirmed the feasibility and broad application prospects of femtosecond laser convenient and efficient preparation of optical negative refraction metamaterials.

Relevant work has been supported by national key research and development plans, the National Natural Science Foundation of China and other projects.

(a) Calculation and measurement of transmissivity and reflectivity of fishing net structure. The green box indicates the magnetic resonance position and the purple box indicates the electric resonance position

(b) Enlarged view of transmission curve, the red arrow is the 2072 nm magnetic resonance position, the yellow arrow is the 2300 nm electrical resonance position, and the green arrow is the 3225 nm magnetic resonance position

Source: Shanghai Institute of Optics and Precision Machinery, Chinese Academy of Sciences