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Antireflective surfaces that are efficient over a broad spectral range with extremely low total reflectivity have abundant potential applications in defense, space, and industries. We successfully fabricated three-dimensional micro-to-nano hierarchical structures on a thin sheet of stainless steel (SS), 100 μm in thickness, by interference-based ultrafast laser patterning for near-perfect absorption. The Sagnac-based interferometer reduces the footprint of the laser on the substrate to smaller than the diffraction limit. In this work, we achieved a groove cut of 13 μm size using a 1030 nm ultrafast laser. We achieved an average total reflectivity of 1.2% over the spectral range of 400–2000 nm and an average specular reflectivity of 0.02% over a broad range of wavelengths of UV–visible–NIR (400–2000 nm) on thin low-weight SS sheets. Further, the average total reflectivity in the spectral region of 400 to 650 nm was 1.1% only. The average groove depth from the top of the surface was 8.5 μm, and most of the material was intact in this process. As these structures are modifications of the same material, they have high mechanical strength and thermal stability and also exhibit self-cleaning ability. The patterned surface is insensitive to incident polarization and has a wide range of acceptance to the incidence cone angle of ±60°. These are the best anti-reflectivity values on an SS surface fabricated via laser surface patterning.

Purpose: To collect and analyze normative data about corneal topography and axial length in various refractive errors in Indian population.Design: Cross-sectional observational study. Materials and Method: Three hundred eyes (150 patients) of age group 12-35 yrs were arranged in 5 groups according to refractive status; Group 1 (n=44): myopia of SphericalEquivalent (SE) > 6 D; Group 2 (n=67): myopia of SE >0.5 D to 6 D; Group 3 (n=88): nearly emmetropic of SE -0.5 D to +0.5 D; Group 4 (n=59): hypermetropia of SE >0.5 to 6 D; Group 5 (n=42): hypermetropia of SE > 6 D. Axial length(AL), central radius of curvature of cornea (CR), central power of cornea (CK) , Al/CR ratio for each group were documented . Correlation with SE and among each other was studied. Results: Mean AL (in mm) of myopic patients (n=111) was 24.23 ± 1.34, emmetropic (n=88) 22.62 ± 0.94 and hypermetropics (n=101) 20.73 ±0.94. Mean CR (in mm) of myopic patients was 7.55 ± 0.35, emmetropics was 7.70 ±0.32, and hypermetropes was 7.99 ±0.35. Mean CK (in D) of myopics was 44.86±2.59, emmetropes was 43.91±1.76, and hypermetropes was 42.32±1.89. Mean AL/CR ratio of myopics was 3.22 ± 0.29, emmetropics 2.94± 0.07, and hypermetropics 2.60 ± 0.19. AL was negatively correlated with SE(r=-0.91, p<0.0001) and positively with AL/CR(r=0.88, p<0.0001) and CK (r=0.36, p<0.0001). CR was negatively correlated with AL/CR (r=-0.74, p<0.0001) while positively correlated with SE (r=0.62, p<0.0001). CK showed positive correlation with AL/CR (r=0.75, p<0.0001) while negative correlation with SE (r=-0.61, p<0.0001). AL/CR was negatively correlated withSE(r=-0.95, p<0.0001). Conclusion: This study showed a negative correlation between axial length and refractive error and between AL/CR ratio and refractive error with stronger inverse relationship in hypermetropes than myopes. There was a positive correlation of CR with SE with a weaker direct relationship in myopes than hypermetropes.