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204 5 Near Field
High temperature region
(Small aperture)
Sufficient Pw
(8.0–9.0mW)
Near field
Recorded mark
(b) Just after writing (c) Super-RENSreading

Lens
(a) Initial condition
(as-depo)
Mask layer
Insufficient Pw Recording layer
(3.0–7.5mW)
(d) Just after writing (e) Super-RENS reading
Fig. 5.47. Working mechanism for aperture-type super-RENS disk obtained from
experimental results. The disk moves from right to left

In summary, both mask and recordinglayers change from as-depo to
amorphous in write process and the mask layer uniformly changes to amor-
phous in read process is presented. Accordingto the conventional superres-
olution mechanism, the very small high temperature region in the focused
spot behaves as an aperture and makes it possible to detect marks less than
diffraction limit on the recordinglayer.

Ag-Super-RENS (Scattered Type)

In this paragraph, following read/write mechanism for the scattered-type
super-RENS optical disk usinga silver oxide (AgO ) mask layer will be
x
presented experimentally: The AgO mask layer has five possible states de-
x
pendingon the input laser power; AgO (as-depo), uniformly dispersed Ag
x
particles (after the initialization of 3.5 mW), Agcluster (4.0–5.0 mW), Agdif-
fusion (5.5–7.5 mW), and Agringstructure (greater than 8.0 mW) for an ob-
jective lens numerical aperture of NA = 0.5, a laser wavelength of λ = 826 nm
and a medium velocity of 2 m s −1 . On the other hand, the GeSbTe record-
inglayer has states; crystal, halfway amorphous, completely amorphous and
gas bubble associated with Ag particles. At the superresolution read power
(4 mW), the mask layer will have Agringstructure that increases both the
CNR and the resolution limit.
A scattered-type super-RENS disk usinga silver oxide (AgO ) mask layer
x
has been proposed to improve the CNR markedly. The small metal particles
in the gas bubble pit formed in write process enhanced the near field (surface
plasmon on the particles) as shown in the upper figure of Fig. 5.48. Ho et al.
found that the functional structure [5.55] of AgO depends on the write power
x
as shown in the lower figure. The aggregated Ag nanocluster (having high
reflectivity due to Agdots) efficiently scatters the near field and the Agring
(havinghigh transmission due to a nanoaperture) not only confines the input