Ultra-high Density Optical Storage Research Articles

Single femtosecond laser pulse–induced valence state conversion in BaFCl: Sm3+ nanocrystals for low-threshold optical storage

Abstract Femtosecond laser-induced valence state conversion (VC) in solid materials has attracted significant research attention due to its potential application in ultra-high density optical storage, boasting advantages such as ultra-high recording speed, easy reading, and high signal-to-noise ratio. However, identifying appropriate materials and technological solutions conducive to efficient single-laser-shot recording remains a pivotal challenge for practical applications. In this work, we report single femtosecond laser pulse–induced VC in BaFCl: Sm3+ nanocrystals utilizing a 4F-configuration optical imaging system comprising two-dimensional scan galvo mirrors. For the first time, we experimentally reveal the luminescence mechanisms and channels of multiphoton absorption-induced Sm2+ ions under both single and multiple 800 nm fs laser pulses. Leveraging the highly efficient single femtosecond laser pulse induced VC, we demonstrate a prototype optical storage experiment by sweeping the recording laser pulse. Remarkably, a threshold pulse energy as low as ∼100 nJ for effective single-laser-shot recording in BaFCl: Sm3+ nanocrystals is obtained under the current experimental conditions. Our investigations offer profound insights into the physical mechanisms underlying femtosecond laser induced VC in solid materials, thereby promoting the prospects of VC based optical storage toward practical applications.

Progress of super-resolution near-field structure and its application in optical data storage

The era of big data has necessitated the use of ultra-high density optical storage devices. Super-resolution near-field structure (super-RENS), which has successfully surpassed the fundamental optical diffraction limit, is one of the promising next generation high-density optical storage technologies. This technology combines the traditional super-resolution optical disk with a near-field structure, and has the advantages of structural simplicity, strong practicability, and, more importantly, compatibility with the current optical storage pickup. The mask layer in super-RENS functions as the key to realizing super- resolution. Development of suitable materials and stack designs has greatly been improved in the last decade. This paper described several types of super-RENS, such as aperture-type, light scattering center-type, bubble-type, and other types (e.g., WOx and ZnO), particularly the newly proposed super-RENS technology and research achievements. The paper also reviews the applications of super-RENS in high-density optical data storage in recent years. After analyzing and comparing various types of super-RENS technology, the paper proposes the aperture- type based on the mechanism of nonlinear optics as the most suitable candidate for practical applications in the near future.

Extraordinary transmission in the ultraviolet range from subwavelength slits on semiconductors

In this paper, we describe a way to achieve the extraordinary transmission regime well into the UV range using subwavelength slits carved on semiconductor substrates. Unlike metals, the dielectric permittivity of typical semiconductors like GaAs or GaP is negative beginning in the extreme UV range (λ≤270 nm) and is characterized by large absorption. We show that the metallike response of bulk semiconductors exhibits surface plasmon waves that lead to extraordinary transmission in the UV and soft x-ray ranges, in spite of the large absorption. The importance of realistic material response versus perfect conductors is also discussed. We show that the use of perfect conductor boundary conditions can lead to field amplitudes that may be underestimated by several orders of magnitudes. These findings may be important in high resolution photolithography, near-field optical devices, and ultrahigh density optical storage in wavelength ranges, where it may not be possible to utilize more traditional plasmonic materials like noble metals.

Photonic Nanojets.

This paper reviews the substantial body of literature emerging since 2004 concerning photonic nanojets. The photonic nanojet is a narrow, high-intensity, non-evanescent light beam that can propagate over a distance longer than the wavelength λ after emerging from the shadow-side surface of an illuminated lossless dielectric microcylinder or microsphere of diameter larger than λ. The nanojet's minimum beamwidth can be smaller than the classical diffraction limit, in fact as small as ~λ/3 for microspheres. It is a nonresonant phenomenon appearing for a wide range of diameters of the microcylinder or microsphere if the refractive index contrast relative to the background is less than about 2:1. Importantly, inserting within a nanojet a nanoparticle of diameter d(ν) perturbs the far-field backscattered power of the illuminated microsphere by an amount that varies as d(ν)3 for a fixed λ. This perturbation is much slower than the d(ν)6 dependence of Rayleigh scattering for the same nanoparticle, if isolated. This leads to a situation where, for example, the measured far-field backscattered power of a 3-μm diameter microsphere could double if a 30-nm diameter nanoparticle were inserted into the nanojet emerging from the microsphere, despite the nanoparticle having only 1/10,000(th) the cross-section area of the microsphere. In effect, the nanojet serves to project the presence of the nanoparticle to the far field. These properties combine to afford potentially important applications of photonic nanojets for detecting and manipulating nanoscale objects, subdiffraction-resolution nanopatterning and nanolithography, low-loss waveguiding, and ultrahigh-density optical storage.

Optical Features of Noble-Metal-Oxide Thin Films Under Irradiation of Blue Laser

The optical reflectance and transmittance of Platinum oxide (PtO(x)) and palladium oxide (PdO(x)) thin films for ultrahigh-density optical storage are investigated using Z-scan technique under irradiation of blue laser (442 nm). The power thresholds of the PtO(x) and PdO(x) decomposition, 3.1 mW and 2.6 mW, are obtained respectively; the PtO(x) (PdO(x)) thin film is reversible and irreversible when input power is less than and more than 3.1 mW (2.6 mW). Deformation analyses by using an atom force microscope (AFM), which is formed in the micro irradiation region of surface on the thin film samples due to decomposition of the PtO(x) or PdO(x) driving the Z-scan, agree well with the Z-scan results. The optical features obtained at 442-nm wavelength are compared with those at 532-nm wavelength, and the threshold difference between the two wavelengths is also analysed in detail based on wavelength-dependent average power density and wavelength-selected absorption of the thin films.

Optical Super-Resolution Technology for Application to Ultra-High Density Optical Storage

Super-resolution technologies for ultrahigh-density optical data storage are described. Applying optical nonlinear thin films, super-resolution readout is attained in less than the optical diffraction limit. In combination with near-field principle, it is further improved in less than 100 nm. In this paper, we discuss the basic principle of near-field optic and related surface and localized surface plasmon polaritons at first, and discribe several applications with metallic nanoparticles and wires to future optical disk technology.

Quantum-Well Photoemission Media for Terabit/inch2 Ultrahigh-Density Optical Storage Employing Probe-Collection Tunneling-Electron Luminescence

For terabit/inch2 ultrahigh-density optical storage with a pit size of less than 25-nm square, we propose probe collection of tunneling-electron luminescence (TL) as a new pickup method. In this method, a probe injects tunneling electrons into a nanometer-sized region in the photoemission medium and the same probe simultaneously collects TL from that region. A semiconductor single quantum well (SQW) has been developed as a photoemission medium that is well-matched with this method. The key features of the SQW medium are (1) a high p-type doping concentration of 2×1019 cm-3 that maximizes the internal quantum efficiency, (2) a flat valence-band edge between the substrate and well for smooth supply of holes to the well, and (3) optimal well depth to maximize probe collection efficiency. Experimental results clarified that tunneling electrons are much better than light for injecting powers into the thin SQW to induce the luminescence, and the use of the SQW instead of bulk material increases the TL intensity at least six times. The TL intensity increases in proportion to tunnel current without saturation at least up to about 30 nA. Consequently, the combination of probe-collection TL with the SQW is believed to be suitable for terabit/inch2 ultrahigh-density optical storage, which requires intense photoemission from nanometer-sized pits.

Investigation on the mechanism of AgO x film super resolution near-field structure

Summary As a promising disk structure for ultrahigh density optical storage, super-resolution near field structure of AgO x type has been studied by both scanning tunneling microscopy and X-ray diffraction experiments. Irregular surface roughness is observed in super-resolution near field structure. And the decomposition of AgO x layer at 160 °C is confirmed. Both results of experiments demonstrate that super-resolution near field structure of AgO x type can satisfy the conditions of exciting surface plasmons.