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Three-dimensional optical memory using a human fingernail

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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.

©2005 Optical Society of America

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Figures (8)

Fig. 1.
Fig. 1. Femtosecond laser processing system.
Fig. 2.
Fig. 2. Multilayered bit arrays at (a) Z=40 µm, (b) Z=60 µm, and (c) Z=80 µm. The scale bar indicates 10 µm.
Fig. 3.
Fig. 3. Side view of the structures formed in a human fingernail with (a) Ep =0.25 µJ, (b) Ep =0.49 µJ, (c) Ep =0.98 µJ, (d) Ep =2.0 µJ, and (e) Ep =3.9 µJ. The scale bar indicates 10 µm. The figure is made of two images that were obtained with adjusting the observation focus to the structures in each images.
Fig. 4.
Fig. 4. Fluorescent image of a side view of the structures formed in a human fingernail. The scale bar indicates 10 µm. The profile is the intensity distribution along a white line in the image. The figure is made of three images that were obtained with adjusting the observation focus to the structures in each images.
Fig. 5.
Fig. 5. Bits recorded by changing focusing position. (a) A transmission-illumination image and (b) a fluorescence image. Atomic force microscope observation images of (c) a pit (Z=5.5 µm) and (d) a swell (Z=6.0 µm). The scale bar indicates 10 µm in (a) and (b), and the side length of figures (c) and (d) is 7.5 µm.
Fig. 6.
Fig. 6. (a) The fluorescence spectra from auto-fluorescence of a fingernail (solid curve) and from the structure formed by femtosecond laser pulse irradiation (dashed curve), and the ratio of fluorescence intensity of the structure and the auto-fluorescence (dotted curve). (b) The fluorescence spectra from fingernails heated at various temperatures (dashed, dotted, dash-dotted, and dash-dot-dotted curves) and a fingernail kept at room temperature (RT, solid curve).
Fig. 7.
Fig. 7. Fluorescence images of 3 bit planes recorded inside human fingernail at (a) Z=40 µm, (b) Z=60 µm, and (c) Z=80 µm. Images were taken 1 day after recording. The scale bar indicates 10 µm.
Fig. 8.
Fig. 8. Fluorescence image taken 172 days after recording. The scale bar indicates 10 µm. The profile is the intensity distribution along a white line in the image.
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