Page 607 - Book Hosokawa Nanoparticle Technology Handbook

38 EXPRESSION OF OPTICAL FUNCTION APPLICATIONS

2+ 5
7
Sm : Do- FJ
3+ 4
6
Sm : G 5/2 - HJ J=0
9/2
7/2 2
Intensity (a.u.) (b) 1
J=5/2

(a) Figure 38.2
The irradiated spot of Sm 2 shown in red color. The
diameter of one circle is about 200 nm. The black color is
occupied by Sm 3 ions in glass samples.
600 700 800
Wavelength (nm)

Figure 38.1
Photoluminescence spectra of the Sm 3 borate glass are written at each 10 layer. Moreover, femtosecond
sample before (a) and after (b) laser irradiation. 3
laser-photoreduced Sm -doped glasses exhibited a
photochemical spectral hole burning memory prop-
erty. The microspot induced by the focused fem-
tosecond laser inside a glass sample can be further
used to store data information via the irradiation of
and other glass samples. In Fig. 38.1 the photolumi- laser light with different wavelengths. As a result, the
3
nescence spectra of the Sm -doped glass sample data information can be read out in the form of spec-
2
before (a) and after (b) laser irradiation show that tral holes. Sm -doped glasses could become an ulti-
only emissions at 560, 600, 645 and 705 nm were mate optical memory device with an ultrahigh
observed in the unirradiated glass sample due to the storage density.
3
4f–4f transitions of Sm . Four new peaks at 683,
700, 724 and 760 nm were observed in the photolu- 2. Precipitation control of gold nanoparticles inside
minescence spectrum of the laser-irradiated glass transparent materials by a femtosecond laser
2
sample due to the 4f–4f transitions of Sm .
Therefore, a part of Sm 3 was converted to Sm 2 Nanoparticles exhibit a wide range of electrical and
after the laser irradiation. The results demonstrated optical properties due to the quantum size effect,
the possibility of selectively inducing a change of surface effect and conjoint effect of the nanostruc-
valence state of Sm 3 ions on the micrometer scale tures. Noble metal nanoparticles doped into materi-
inside a glass sample by use of a focused nonresonant als exhibit large third-order nonlinear susceptibility
femtosecond pulsed laser as shown in Fig. 38.2. On and ultrafast nonlinear response. They are expected
the other hand, a three-dimensional optical memory to be promising materials for ultrafast all-optical
3
has approximately 10 13 bits/cm storage density, switches in the THz region. Nanoparticles need to
which means that data information can be stored in be arranged into well-defined configurations or to
the form of a change in refractive index in a spot; be distributed space-selectively in materials in order
optical memory using a valence-state change of rare- to build integrated systems. Up to now, many
earth ions in a spot may have the same storage den- studies have been carried out on the fabrication of
sity and allow one to read out data in the form of nanoparticle-doped materials. However, there are
luminescence, thus providing the advantage of a high no effective methods of preparation so that the
signal-to-noise ratio. Therefore, the present tech- distribution of nanoparticles is space-selectively
nique will be useful in the fabrication of three- well controlled. The authors demonstrated three-
dimensional optical memory devices with high dimensional precipitation and control of nanoparti-
storage density. One example by using the characters cles in materials by using focused femtosecond
of A, B and C is shown in Fig. 38.3. These characters laser irradiation and successive annealing in detail.

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