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Application of femtosecond-laser induced nanostructures in optical memory

Application of femtosecond-laser induced nanostructures in optical memory
Application of femtosecond-laser induced nanostructures in optical memory
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 µm/ns). We have also observed the localized photo-reduction of Sm3+ to Sm2+ inside a transparent and colorless Sm3+-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 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.
1533-4880
94-104
Shimotsuma, Yasuhiko
0664279b-def2-41d4-a5ec-207ce02013a7
Sakakura, Masaaki
3bb15bbd-d590-4cba-ab5a-862dc7acd054
Miura, Kiyotaka
5dbc9159-ace0-4dd9-b18d-36f87ae78c47
Qiu, Jiarong
befa87a1-4795-4e67-b74f-81239eee689c
Kazansky, Peter G.
a5d123ec-8ea8-408c-8963-4a6d921fd76c
Fujita, Koji
3419a269-88e1-4670-8075-93d6c3588ba3
Hirao, Kazuyuki
5cc5061d-6217-49ae-bc92-ff5b72b9c6c2
Shimotsuma, Yasuhiko
0664279b-def2-41d4-a5ec-207ce02013a7
Sakakura, Masaaki
3bb15bbd-d590-4cba-ab5a-862dc7acd054
Miura, Kiyotaka
5dbc9159-ace0-4dd9-b18d-36f87ae78c47
Qiu, Jiarong
befa87a1-4795-4e67-b74f-81239eee689c
Kazansky, Peter G.
a5d123ec-8ea8-408c-8963-4a6d921fd76c
Fujita, Koji
3419a269-88e1-4670-8075-93d6c3588ba3
Hirao, Kazuyuki
5cc5061d-6217-49ae-bc92-ff5b72b9c6c2

Shimotsuma, Yasuhiko, Sakakura, Masaaki, Miura, Kiyotaka, Qiu, Jiarong, Kazansky, Peter G., Fujita, Koji and Hirao, Kazuyuki (2007) Application of femtosecond-laser induced nanostructures in optical memory. Journal of Nanoscience and Nanotechnology, 7 (1), 94-104. (doi:10.1166/jnn.2007.18008).

Record type: Article

Abstract

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 µm/ns). We have also observed the localized photo-reduction of Sm3+ to Sm2+ inside a transparent and colorless Sm3+-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 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.

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Published date: January 2007

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Local EPrints ID: 46863
URI: http://eprints.soton.ac.uk/id/eprint/46863
ISSN: 1533-4880
PURE UUID: 80d4b5c8-b964-4fb0-bf87-5bdae038742b

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Date deposited: 20 Jul 2007
Last modified: 08 Jun 2020 16:32

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Contributors

Author: Yasuhiko Shimotsuma
Author: Masaaki Sakakura
Author: Kiyotaka Miura
Author: Jiarong Qiu
Author: Koji Fujita
Author: Kazuyuki Hirao

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