Use of continuous-wave illumination for two-photon three-dimensional optical bit data storage in a photobleaching polymer

Reversible Mn valence state switching in submicron α-Al2O3:Mn by soft X-rays and blue light - a potential pathway towards multilevel optical data storage

The generation of Mn⁴⁺ in α-Al₂O₃:Mn³⁺ by soft X-ray exposure is demonstrated with a large dynamic range of the X-ray generated Mn⁴⁺ luminescence signal, indicating the potential use of α-Al₂O₃:Mn³⁺ for multilevel optical data storage. Samples with a range of Mn concentrations (0.05, 0.1, 0.2, 0.4, 0.6 and 1.2 atom%) were prepared via a facile combustion method and the sample with 0.4 atom% was found to display the highest luminescence intensity. The stored information can be read out via the R-lines (²E → ⁴A₂) under ∼470 nm (⁴A₂ → ⁴T₂), or ∼630 nm (⁴A₂ → ²T₁) excitation with the latter being preferred since photobleaching is minimized. Interestingly, the Mn⁴⁺ valence state can be fully switched back to Mn³⁺ by blue light exposure (e.g., 462 nm laser diode). The stored information could be repeatedly written and erased, showing no significant deterioration over five consecutive cycles, with less than 5% uncertainty.

Ultra-high capacity for three-dimensional optical data storage inside transparent fluorescent tape

In this Letter, we show an ultralarge capacity for three-dimensional optical data storage inside transparent fluorescent tape using the two-photon absorption photo-bleaching method. We can obtain transparent fluorescent tape by means of the simple dip method. We successfully demonstrate recording and reading of six layers of binary data bits with lateral separation of 2 µm and longitudinal layer separation of 3 µm. Thus, this result leads to a storage density of approximately ${80}\;{{\rm Gbits/cm}^3}$80Gbits/cm³. Therefore, we can realize authentic ultrahigh capacity optical data storage using long transparent fluorescent tape in the future, like magnetic tape, and fundamentally solve the data explosion disaster.

Multiphoton microscopy as a detection tool for photobleaching of EO materials

Multi-photon microscopy operating at 1550 nm is employed as a rapid characterization tool for studying the photostability of three well-known electro-optical materials. Different nonlinear optical responses such as multi-photon excitation fluoresence, second-, and third-harmonic generation can be used as detection probes to reveal the degradation mechanisms. This technique is rapid, accurate, and can be used to study the photostability of a broad range of materials.

Substituent Effect on the Photobleaching of Pyrylium Salts under Ultrashort Pulsed Illumination

The current article presents the photobleaching properties of a group of pyrylium salts under ultrashort pulsed illumination. These pyrylium salts have the same basic chemical structure and differ only by a specific substituent. It is proven experimentally that two different mechanisms are simultaneously present to the photobleaching of all molecules studied (independently of their specific chemical structure). However, the particular parameters of each mechanism are influenced significantly by the substituent change. The experimental investigation of these parameters showed the presence of multiphoton interactions in the photobleaching of pyrylium salts depending essentially on the specific substituent.

Two-Photon Absorption Properties of Self-Assemblies of Butadiyne-Linked Bis(Imidazolylporphyrin)

Supramolecular porphyrin self-assemblies have been prepared from butadiyne-linked bis(imidazolylporphyrin) by complementary coordination of imidazole to zinc, and their two-photon absorption (2PA) and higher-order nonlinear absorption properties were investigated over femtosecond time scales using an open-aperture Z-scan method. The self-assembled porphyrin dimer of the conjugated monozinc bisporphyrin 7D was shown to have a large 2PA cross section (7.6 x 10(3) GM, where 1 GM = 10(-50) cm(4) s molecule(-1) photon(-1)) at 887 nm. By comparison of this result with that for a meso-meso-linked porphyrin array without the butadiyne connection (3.7 x 10(2) GM at 964 nm), it was demonstrated that the predominant factor in this significant enhancement of the cross section was the expansion of porphyrin-porphyrin pi-conjugation. Self-coordination and monozinc metalation were also found to be contributing factors. Furthermore, a novel self-assembled porphyrin polymer 8P consisting of a biszinc complex with a mean molecular weight of M(n) = 1.5 x 10(5) Da was shown to exhibit an extraordinarily large two-photon absorption cross section (4.4 x 10(5) GM at 873 nm). Nanosecond Z-scan experiments for 7D and 8P were also undertaken and resulted in the measurement of large effective 2PA cross sections, including the excited-state absorption (2.1 x 10(5) GM for 7D and 2.2 x 10(7) GM for 8P, respectively). Finally, three-photon absorption was observed by femtosecond Z-scan experiments at 1188 nm (7.1 x 10(-89) m(6) s(2)) and 1282 nm (1.8 x 10(-89) m(6) s(2)), an observation which is the first of its kind in porphyrin chemistry.

Light propagation in a multilayered medium for three-dimensional optical memory

We report on the optimization of film thicknesses in a multilayered medium to increase readout signal intensity. The multilayered medium consists of a stack of photosensitive and transparent films, arranged alternately. The thicknesses of the photosensitive and transparent films in the multilayered medium were optimized for a reflection confocal system to read out data by analyzing the propagation of light focused into a multilayered medium.

Three-photon induced photobleaching in a three-dimensional memory material

The photobleaching properties of a 3D memory material based on pyrylium salts are studied. It is shown that under ultrashort pulsed irradiation photobleaching occurs through two diverse mechanisms. One is major and causes fast bleaching, whereas the other is minor and causes slow bleaching. Furthermore, it is proved that both mechanisms are three- or more-photon processes. This fact gives the capability of significantly increasing data storage density.

Compact confocal readout system for three-dimensional memories using a laser-feedback semiconductor laser

We present a compact confocal readout system for three-dimensional optical memories that uses the thresholding property of a semiconductor laser for feedback light. The system has higher axial resolution than a conventional confocal system with a pinhole. We demonstrate readout results for data recorded in two recording layers with the developed system.

Precision measurement of the electromagnetic fields in the focal region of a high-numerical-aperture lens using a tapered fiber probe

We present a measurement of the intensity around the focus of a N.A.-0.95 lens using a tapered optical fiber probe. An asymmetry introduced by the vector nature of the incident polarized light is evident, although it is inconsistent with that predicted theoretically by considering the magnitude squared of the electric field. The sensitivity of the probe to different components of the electromagnetic field is considered, and it is shown that the measurement is consistent with vector diffraction theory when the probe properties are taken into account.

Multi-photon fluorescence microscopy--the response of plant cells to high intensity illumination

Multi-photon fluorescence microscopy has been cited for its advantage in increased depth penetration due to low linear absorption and scattering coefficient of biological specimen in the near infrared (NIR) range. Because of the need of high peak power for efficiently exciting two-photon fluorescence, the relationship between cell damage and peak power has become an interesting and much debated topic in the applications of multi-photon fluorescence microscopy. It is conceivable that at high illumination intensity, non-linear photochemical processes have impacts on cell physiology and viability in ways much different from low illumination in the linear domain. In this article, we discuss some of the issues in two-photon fluorescence microscopy, including the degree of transparency of the specimen, a comparison of single- and two-photon excited fluorescence spectra, and the cell damage under high intensity illumination, using plant cells as a model.

Use of two-photon excitation for erasable-rewritable three-dimensional bit optical data storage in a photorefractive polymer

We report what is believed to be the first use of a photorefractive polymer in erasable-rewritable three-dimensional bit optical data storage under two-photon excitation. We successfully demonstrate writing, erasing, and rewriting of multilayered information in a photorefractive polymer consisting of 2,5-dimethyl-4-(p-nitrophenylazo)anisole, 2,4,7-trinitro-9-fluorenone, 9-ethylcarbazole, and poly(N-vinylcarbazole). A three-dimensional bit density of 5 Gbits/cm(3) is achieved by two-photon absorption under pulsed beam illumination at an infrared wavelength of 800 nm in the recording process. Complete erasing of the recording information is achieved by use of ultraviolet illumination.