In big data center, optical storage technologies have many advantages, such as energy saving and long lifetime. However, how to improve the storage density of optical storage is still a huge challenge. Maybe the multilayer optical storage technology is the good candidate for big data center in the years to come. Due to the number of layers is primarily limited by transmission of each layer, the largest capacities of the multilayer disc are around 1 TB/disc and 10 TB/ cartridge. Holographic data storage (HDS) is a volumetric approach, but its storage capacity is also strictly limited by the diffractive nature of light. For a holographic disc with total thickness of 1.5mm, its potential capacities are not more than 4TB/disc and 40TB/ cartridge. In recent years, the development of super resolution optical storage technology has attracted more attentions. Super-resolution photoinduction-inhibition nanolithography (SPIN) technology with 9 nm feature size and 52nm two-line resolution was reported 3 years ago. However, turning this exciting principle into a real storage system is a huge challenge. It can be expected that in the future, the capacities of 10TB/disc and 100TB/cartridge can be achieved. More importantly, due to breaking the diffraction limit of light, SPIN technology will open the door to improve the optical storage capacity steadily to meet the need of the developing big data center.
In this work, an optical system with large diameter off-axis parabolic lenses was adopted to achieve diffraction gratings by laser interference exposure. The diffraction wavefront aberration caused by temperature variations was simulated using ZEMAX. Through theoretical analysis and optical simulation, it is proved that the diffraction wavefront aberration of holographic grating caused by the pinhole’s location errors (it is assumed that when the displacement of pinhole exists along one axis, the locations of the pinhole along the other two orthogonal axes are in a state of precise adjustment ) is much larger when the displacement occurs along z axis than along the other two axes, and the diffraction wavefront aberration is the smallest when the displacement occurs along x axis. If the ambient temperature changes by 1 degree, the PV value is 0.0631λ when the location of the pinhole changes by 0.121mm along z axis, 0.0034λor 0.0672λ when the location of the pinhole changes by 0.002mm along x axis or 0.03mm along y axis. To reach the diffraction limit (that means the PV value is 0.25λ), the decentering value of the pinhole along z axis should be less than 0.0341mm. In conclusion, the position error along z axis is an important factor to influence the PV value of diffraction grating, and the effect of temperature on the PV value of diffraction grating can be neglected.
Damages on or near polished substates can be easily observed by TIRM(Total Internal Reflection Microscopy). In our experiments we found that there was a strong dependence of scratch visibility on the angle(φ) between scratches and normal direction of the incident plane. In this paper, the scattered field distribution of a scratch and the imaging properties of a microscope are analyzed. We believe that it is the anisotropy of illumination in TIR-illumination mode that causes the visibility changes of a scratch. After taking this directionality into consideration, we propose an experimental method for TIRM to take picutures with all scratches in all directions in one image.
The laser induced damage threshold (LIDT) and damage morphology of the monolayer coating are easily influenced by
the finish condition of the substrate, which makes it difficult to compare the LIDT of different coating materials. In order
to eliminate the influence of defect and sub-defect on the substrate, HfO2, Sc2O3, Y2O3, Al2O3 and SiO2 monolayer
coatings were prepared on 1064 nm HfO2/SiO2 high reflection coatings, using conventional e-beam deposition. The LIDT, as well as the damage morphology after laser irradiation at wavelength of 1064 nm, was measured and compared with that of the monolayer coating deposited on BK7 glass substrate.
The laser-induced damage threshold (LIDT) of optical thin film is influenced by certain preconditioning processes.
HfO2/SiO2 532nm high reflective multi-layers were prepared by electron beam evaporation and were preconditioned by
532nm laser. The 532nm LIDT, surface condition, and damage morphology of the sample were characterized and
compared before and after laser conditioning process. Results are presented that the LIDT of e-beam deposited
multilayer HfO2/SiO2 thin films can be increased after laser conditioning. Possible reasons for such enhancement have been analyzed.