Alexander S. Dvornikov

Two-Photon Three-Dimensional Optical Storage Memory

We describe the design and construction of ultrahigh capacity three-dimensional, 3D, optical storage devices that operate by two-photon absorption. The molecular systems and their properties that are used as two photon media for writing and one photon for accessing the stored information within the volume of the device are presented in some detail and the nonlinear two-photon absorption mechanism is briefly visited. The optical system and its components, which facilitated writing and reading, are also described and the bit density, bit error rate, store and access speeds, cycle times, and stability of the materials under various experimental conditions are also topics addressed in this review. The first ever storage of terabyte data in a removable storage disk is described in detail.

Observations on the measurement of two-photon absorption cross-section

We have measured two-photon absorption (TPA) cross-sections of four organic molecules in solution. The data show that the nonlinear transmission method without consideration of other nonlinear effects results, under certain conditions, in erroneous values for the TPA cross-sections. We also find that the cross-sections measured by excited-state methods, namely two-photon induced fluorescence and a new excited-state method, which is based on transient spectroscopy following two-photon excitation, are in good agreement with the published data. Therefore, caution is warranted when using the transmission method.

Accessing 3D memory information by means of nonlinear absorption

A novel method for accessing information from two-photon 3D volume memory devices is presented. We have used the decrease in laser intensity induced by two-photon absorption as the means for reading 3D information. The ratio of the initial laser intensity to the intensity after two-photon absorption is increased drastically by passing both beams through a second and fourth harmonic crystal. This means eliminates the need for focusing and collecting lenses and the disadvantages associated with the fluorescence method of reading information.

Nonvolatile read-out molecular memory

A versatile molecule is described that performs as a nondestructible read-out optical-storage molecular memory. This molecular memory is composed of two distinct molecules that are chemically bonded to each other to form a single molecule with unique properties. One component is a photochromic fulgimide, and the other is a strongly fluorescing oxazine dye. This composite molecule was specifically designed and synthesized to display, under specific conditions, both the photochromic functions of the first component and the fluorescence properties of the dye. To store information, the polar, closed form of the photochromic component is illuminated with 530-nm light, which converts it to the open, nonpolar form. The information is accessed by excitation at the 650-nm band of the oxazine dye component, causing the dye to fluoresce. However, the dye emits intense fluorescence under a nonpolar environment, which is attained only when the fulgimide component is in its open, nonpolar structure. The ultrafast kinetics, spectroscopy, and mechanism of the photoreaction of this molecule and its photoinduced intermediates have been measured, and fluorescence quantum yields and cross sections were determined.

Novel organic ROM materials for optical 3D memory devices

Abstract We describe novel optical memory materials which we developed for Read Only Memory (ROM) computer storage applications. Their optical and spectroscopic properties are briefly described and the utilization of these ROM materials in 3D optical storage devices, by means of two-photon absorption, is demonstrated.

Terabyte recorded in two-photon 3D disk.

1 Tbyte of data has been recorded in 200 layers inside the volume of one of our two-photon 3D disks. Each layer contains 5 Gb of data similar to the capacity of a single layer DVD. The results obtained with our high-performance 1.0 numerical aperture (NA) objective lens show a full disk recording of 1 Tbyte within a standard optical disk form factor 120 mm x 1.2 mm thick utilizing our very stable and efficient materials. Very high sensitivity materials are recorded with bit energies as low as 250 pJ/bit. Materials sensitive at 405 nm are experimentally tested by recording with a 405 nm Nichia laser diode. Results show that bit dimensions are further reduced, which enables future recordings of 5 Tbyte disk capacities by recording 25 Gb/layer, the equivalent of a Blu-ray disk capacity per layer.

Experimental characterization of a two-photon memory

We demonstrate the recording of 100 planes of digital images in a page-oriented two-photon memory and characterize the images in terms of signal-to-noise ratio and bit error rate. Possible error sources in the recording are discussed, and methods for compensating for some of these effects are presented. Looking at the distributions of the normalized bit intensities, we are able to estimate the minimum achievable bit error rate for this system.

A novel non-destructible readout molecular memory

Abstract We describe briefly, the mechanism and characteristics of a versatile new photochromic molecule that is capable of performing as a medium for non-destructible high capacity readout molecular storage devices. This molecular memory consists of two different molecular components, chemically bonded together. It retains the photochromic and spectroscopic properties of each individual molecular component and the changes in the property of one component influence the fluorescence quantum yield of the other. The write form is a polar closed structure molecule that does not fluoresce. When transformed into the read form it exhibits an open structure, is non-polar and allows for intense fluorescence. The read form excited state is located at 660 nm, which is at lower energy than the excited state of the write form, therefore no erasing occurs while reading. Erasing is achieved by excitation at 400 nm, which is higher than 530 nm write energy. The write/read/erase spectra and mechanism have been measured in solution and in solid polymer, including PMMA matrices.

Toward terabyte two-photon 3D disk.

253GB have been recorded in 300 layers inside the volume of one of our two-photon 3D disks. Each layer contains the equivalent of CD layer bit-densities recorded with a 0.5NA objective lens. A new 1.0NA lens with the desirable first order optical properties of long working distance and small diameter, 1.2mm and 4.5mm, and a self-compensating spherical aberration correction mechanism is designed, manufactured and integrated into our single beam two-photon 3D automated recording system. Experimental data obtained with the 1.0NA lens are presented. The resulting bit densities obtained with our new high-performance liquid immersion singlet (LIS) objective lens indicate that our system is capable of full disk recordings from 0.5 to 1 TB within a standard optical disk form factor of 120mm x 1.2mm thick utilizing our very stable and efficient materials. A compact optical head based on our new objective lens capable of TB storage is described.

Laser nanosurgery of single microtubules reveals location-dependent depolymerization rates

In this study, 532-nm picosecond and 800-nm femtosecond lasers are used in combination with fluorescently labeled tubulin to further elucidate microtubule depolymerization and the effect lasers may have on the resulting depolymerization. Depolymerization rates of targeted single microtubules are dependent on location with respect to the nucleus. Microtubules located near the nucleus exhibit a significantly faster depolymerization rate when compared to microtubule depolymerization rates near the periphery of the cell. Microtubules cut with the femtosecond laser depolymerize at a slower rate than unirradiated controls (p=0.002), whereas those cut with the picosecond laser depolymerize at the same rate as unirradiated controls (p=0.704). Our results demonstrate the ability of both the picosecond and femtosecond lasers to cut individual microtubules. The differences between the two ablation results are discussed.