Femtosecond lasers and their applications for optical memory

Femtosecond lasers and their applications for optical memory - examples of research are presented below.

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Precision Optical Components, Crystals and Wafers
We offer variety of materials that can be used for optical data storage. Please e-mail us with your inquiry.
Optics from A to Z - just few examples of our capabilities.
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Femtosecond Laser Structuring of As2S3 Glass for Erasable and Permanent Optical Memory

Saulius Juodkazis, Andrei V. Rode, Toshiaki Kondo, Hiroaki Misawa, Marek Samoc, Barry Luther-Davies
The nonlinear absorption coefficient of As2S3 glass has been measured to be 2.0 cm/GW for femtosecond pulses at 800 nm. Femtosecond laser structuring via two photon absorption in bulk As2S3 glass by erasable and permanent photo-darkening is demonstrated using both holographic and direct multi-beam laser writing.

Three-dimensional optical memory using a human fingernail
Akihiro Takita, Hirotsugu Yamamoto, Yoshio Hayasaki, Nobuo Nishida, and Hiroaki Misawa
Optics Express, Vol. 13, Issue 12, pp. 4560-4567

Keywords (OCIS):
(140.7090) Lasers and laser optics : Ultrafast lasers
(210.4680) Optical data storage : Optical memories
(300.6280) Spectroscopy : Spectroscopy, fluorescence and luminescence

Abstract
We realized optical data storage in a human fingernail. A structural change is recorded by irradiating a focused femtosecond laser pulse and is read out with fluorescent observation by making use of an increased fluorescence intensity. The shape of the structural changes drastically depends on the irradiated pulse energy. The fluorescence spectrum of the structure coincided with the auto-fluorescence spectra of a fingernail and a heated fingernail. It is suggested that the increased fluorescence is most likely caused by a local denaturation of the keratin protein by the femtosecond laser pulse irradiation. We demonstrate that the increased fluorescence effect is useful for reading out three-dimensionally recorded data.

Femtosecond laser induced PL change in Sm-doped sodium borate glass and 3D optical memory

Seungphil Lee a, b, Myeongkyu Leea, and Kisoo Limb
a Department of Materials Science and Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-ku, Seoul 120-749, Korea
bDepartment of Physics, Chungbuk National University, 48 Gaesin-dong, Cheongju, Chungbuk 361-763, Korea

Abstract

We report on a femtosecond laser-induced photoluminescence (PL) change in Sm-doped sodium-borate glass and its potential application to three-dimensional optical memory. Irradiation with a femtosecond pulsed laser (800 nm, 1 kHz, 100 fs) induced a new PL peak near 682 nm, resulting from the photoreduction of Sm ions from Sm3+ to Sm2+. This makes it possible to readout the stored data by detecting the new PL peak as a signal. Multilayer patterns of various dot sizes and interlayer spacings were fabricated by femtosecond pulsed laser. These patterns were read out by a fluorescent confocal microscope which detected the emission at 682 nm as a signal. Here we discuss the feasibility of 3D optical memory by use of PL change in Sm-doped sodium borate glass.

Keywords: 3D optical memory; Femtosecond laser; Photoluminescence change

Application of femtosecond-laser induced nanostructures in optical memory.
Shimotsuma Y, Sakakura M, Miura K, Qiu J, Kazansky PG, Fujita K, Hirao K.

Fukui Institute for Fundamental Chemistry, Kyoto University, Nishihiraki-cho 34-4, Takano, Sakyo-ku, Kyoto 606-8103, Japan.

The femtosecond laser induced micro- and nanostructures for the application to the three-dimensional optical data storage are investigated. We have observed the increase of refractive index due to local densification and atomic defect generation, and demonstrated the real time observation of photothermal effect after the femtosecond laser irradiation inside a glass by the transient lens (TrL) method. The TrL signal showed a damped oscillation with about an 800 ps period. The essential feature of the oscillation can be reproduced by the pressure wave creation and propagation to the outward direction from the irradiated region. The simulation based on elastodynamics has shown that a large thermoelastic stress is relaxed by the generation of the pressure wave. In the case of soda-lime glass, the velocity of the pressure wave is almost same as the longitudinal sound velocity at room temperature (5.8 microm/ns). We have also observed the localized photo-reduction of Sm3+ to Sm2+ inside a transparent and colorless Sm(3+)-doped borate glass. Photoluminescence spectra showed that some the Sm3+ ions in the focal spot within the glass sample were reduced to Sm2+ ions after femtosecond laser irradiation. A photo-reduction bit of 200 nm in three-dimensions can be recorded with a femtosecond laser and readout clearly by detecting the fluorescence excited by Ar+ laser (lambda = 488 nm). A photo-reduction bit can be also erased by photo-oxidation with a cw Ar+ laser (lambda = 514.5 nm). Since photo-reduction bits can be spaced 150 nm apart in a layer within glass, a memory capacity of as high as 1 Tbit can be achieved in a glass piece with dimensions of 10 mm x 10 mm x 1 mm. We have also demonstrated the first observation of the polarization-dependent periodic nanostructure formation by the interference between femtosecond laser light and electron acoustic waves. The observed nanostructures are the smallest embedded structures ever created by light. The period of self-organized nanostructures can be controlled from approximately 140 to 320 nm by the pulse energy and the number of irradiated pulses. Furthermore, we have also observed the self-assembled sub-wavelength periodic structures created in silica glass by femtosecond pulses on the plane of the propagation of light.

Bulk photochromism in a tungstate-phosphate glass: A new optical memory material?
J. Chem. Phys. 125, 161101 (2006); DOI:10.1063/1.2364476
Published 30 October 2006

Gaël Poirier
Departamento de Ciências Exatas, Universidade Federal de Alfenas, UNIFAL CEP 37130–000, Alfenas-MG, Brazil

Marcelo Nalin and Lucila Cescato
Laboratory of Optics, Department of Physics of Condensed Matter, Instituto de Física Gleb Wataglin, UNICAMP, PoBox 6165, CEP 13083-970, Campinas SP, Brazil

Younes Messaddeq and Sidney J. L. Ribeiro
Laboratory of Photonic Materials, Instituto de Química, UNESP, PoBox 355, CEP 14800-900, Araraquara SP, Brazil

In this work, we present a new photochromic tungstate based glass which have both absorption coefficient and refractive index modified under laser exposure. The photosensitive effect is superficial under ultraviolet (UV) irradiation but occurs in the entire volume of the glass under visible irradiation. The effect can be obtained in any specific point inside the volume using an infrared femtosecond laser. In addition, the photosensitive phenomenon can be erased by specific heat treatment. This glass can be useful to substitute actual data storage supports and is a promising material for 3-dimensional (3D) and holographic optical storage.

Femtosecond Photonics: Microfabrication and Optical Data Storage