We propose a sub-wavelength range-based dual-band tunable ideal terahertz metamaterial perfect absorber. The absorber structure consists of three main layers, with the absorber layer consisting of a metal I-shaped structure. By simulating the incident wave absorbance of the structure, we found that the structure has more than 99% absorption peaks in both bands. In addition, we have investigated the relationship between structural absorbance and the structural geometrical parameters. We have studied the relationship between the thickness of the metal absorber layer $h_b$ and the absorbance of the metamaterial structure in the 4–14 THz band. Secondly, we have studied the relationship between the thickness of the SiO₂ dielectric layer and structural absorbance. Afterwards, we have studied the relationship between the incident angle of the incident electromagnetic wave and structural absorbance. Finally, we have studied the relationship between the length of the metal structure and structural absorbance. The structure can be effectively used for detectors, thermal emitters, terahertz imaging and detection.

Femtosecond laser processing technology is an advanced sub-micro-processing technique that enables the non-contact processing of various materials. This technology can be used to apply sub-micro structures for purposes such as hydrophilicity enhancement, optical transmittance improvement, and photonics detection. However, when it comes to processing micro/nanostructures on highly brittle materials using femtosecond lasers, there are challenges such as low processing efficiency, generation of debris, and microcracking. In this paper, we propose a method called the out-of-focus femtosecond laser direct writing technique combined with wet etching. This method offers simplicity, speed, and flexibility in preparing dense, large-area sub-microstructured surfaces on the brittle material sapphire. Our detailed investigation focuses on the impact of laser processing parameters (direct writing period, distance of focusing, direct writing speed, etc.) on the sub-microstructures of Al₂O₃ surfaces. The results demonstrate that this method successfully creates embedded sub-microstructures on the sapphire surface. The microholes, with a diameter of approximately 2.0 μm, contain sub-micro structures with a minimum width of 250 ± 20 nm. Additionally, we conducted experiments to assess the optical transmittance of sapphire nanostructures in the range of 350–1200 nm, which exhibited an average transmittance of approximately 77.0%. The water contact angle (CA) test yielded a result of 52 ± 2°, indicating an enhancement in the hydrophilicity of the sapphire nanostructures with only a slight reduction in optical transmittance. Our efficient fabrication of sub-microstructures on the sapphire surface of highly brittle materials offers a promising method for the production and application of brittle materials in the field of micro-optics.

A femtosecond laser raster-type in situ repetitive direct writing technique was used for the fabrication of anti-reflective microhole structures in Germanium (Ge) in the visible near-infrared range (300–1800 nm). This technique builds a layer of microstructured arrays on the surface of Ge, enabling Ge to exhibit excellent anti-reflective properties. The large-area micro-nanostructures of Ge were fabricated using femtosecond laser raster-type in situ repetitive direct writing. Ge microstructures are characterized by their structural regularity, high processing efficiency, high reproducibility, and excellent anti-reflective properties. Experimental test results showed that the average reflectance of the Ge microporous structure surface in the range of 300–1800 nm was 2.25% (the average reflectance of flat Ge was 41.5%), and the lowest reflectance was ~1.6%. This microstructure fabrication drastically reduced the optical loss of Ge, thus enhancing the photothermal utilization of Ge. The many nanoburrs and voids in the Ge microporous structure provided excellent hydrophobicity, with a hydrophobicity angle of up to 133 ± 2° (the hydrophobicity angle of flat Ge was 70 ± 2°). The high hydrophobicity angle allows for strong and effective self-cleaning performance. The femtosecond laser raster-type in situ repeatable direct writing technology has many desirable properties, including simplicity, high accuracy, flexibility, and repeatability, that make it one of the preferred choices for advanced manufacturing. The Ge micro-nanostructured arrays with excellent optical anti-reflective properties and hydrophobicity have become an attractive alternative to the current photo-thermal absorbers. It is expected to be used in many applications such as solar panels, photovoltaic sensors, and other optoelectronic devices.

The fabrication of SSD-free fused silica optics is a crucial objective for high-power laser applications. To treat the surface of polished fused silica, a combination of RIE/RIBE and deep-controlled etch (DCE) techniques are typically employed. Currently, it is important to consider and study the ideal etching depth and precision while using combined etching techniques to remove the identified SSD. Herein, we present a novel approach to identify the distribution of SSD in fused silica, which corresponds to a specific grinding/polishing process condition. Our method involves using a mobile RIBE to perform cone cutting and remove material from the polished fused silica surface. Afterward, we etch the optical element’s surface with HF to visualize the subsurface cracks and understand their relationship with the RIBE depth. Through a systematic investigation of the combined etching technique, we establish a correlation between the depth of RIBE and DCE and the performance of laser damage. The combined etching technique can be implemented as a dependable approach to treat the surface/subsurface defects in fused silica and has the potential to improve laser damage resistance significantly.

In high-power laser systems, the loading capacity of fused silica components under 351 nm irradiation is an important factor limiting their ability to increase output power, and in the current study, the damage threshold enhancement of fused silica components after RIE and AMP treatments has been investigated. Sub-surface defects in fused silica components after RIE treatment have also been investigated, but the reason for the high damage threshold could never be explained. Since quartz crystals and fused silica belong to the same silica system, and quartz crystals have more characterisation means than fused silica, we can extrapolate to fused silica by studying quartz crystals. We can extrapolate to fused silica by studying quartz crystals, which are characterised by more means than fused silica, and prove that the extrapolation is correct by characterising fused silica. In this study, the relationship between the etching process and the damage threshold is concluded by studying different RIE etching processes, and the damage threshold of the samples is optimal when the etching depth is 1 um.

After the plasma etching of quartz crystal, the crystal lattice underwent changes in response to the length of plasma etching time. The lattice arrangement of quartz crystal was the most orderly after plasma etching for 1000 nm, and with the increase in etching time, the lattice arrangement became less orderly again. The weak absorption value of quartz crystal was also consistent with this conclusion. In this paper, we investigated the effect of lattice changes on the damage threshold of quartz crystals by characterizing the quartz crystals using Reactive Ion Etching (RIE). We also examined the effect of lattice variation on roughness and surface topography.