Page 585 - Book Hosokawa Nanoparticle Technology Handbook

32 DEVELOPMENT OF OPTICAL MEMORY APPLICATIONS

4 3.5
3.5
3
3
2.5
2.5
2
I/I o 2 I/I 0
1.5
1.5
1 Result of writing with an intensity of 11 nW 1
Result of writing with an intensity of 220 nW
0.5 0.5 Result of writing with an intensity of 11nW
Result of writing with an intensity of 1370 nW
Result of writing with an intensity of 1370 nW
0
0 200 400 600 800 0
Total energy radiated during the writing operation (nJ) 0 1000 2000 3000 4000 5000
Total energy radiated during the writing operation (nJ)
Figure 32.3
Multiple-value recording of fluorescence intensity due to Figure 32.4
writing operation using different excitation light Rewriting of recorded value by alternatingly irradiating
intensities. with an excitation light having an intensity of 11 nW and
an excitation light having an intensity of 1,370 nW.

writing operation is repeated and gets saturated at excitation light having a different intensity, that is,
an I/I value of about 3.0. that it is possible to rewrite the recorded value.
0
On the other hand, when an excitation light having
an intensity of 1,370 nW is used, although the fluo- 5. Future topics
rescence intensity increases in a similar manner, it
reaches saturated value I/I of about 1.5. This attained The two features of multiple-value recording and
0
an intermediate value of I/I of about 1.8 when excited rewriting were described above in an optical memory
0
with light having an intermediate intensity of 220 nW. device using semiconductor nanoparticles. The prob-
From the above results, it is shown that multiple-value lem that has to be solved in the future is that of stor-
recording of fluorescence intensity is possible by ing the recorded value for a long time. In the present
changing the excitation light intensity. stage, it has only been reported that the value can be
Next, Fig. 32.4 shows the result of writing again stored for a period of only about a few months, and it
using an excitation light having an intensity of 1,370 is necessary to realize a storage period on the order of
nW in the same area after recording a fluorescent several tens of years in order to realize practical prod-
intensity of I/I of about 3.0 in an area of about ucts. At the same time, it has also been reported that
0
2
7.4 m using an excitation light having an intensity the optical characteristics of semiconductor nanopar-
of 11 nW. The fluorescence intensity that increased up ticles are strongly dependent on the surrounding envi-
to an I/I value of about 3.0 due to the writing opera- ronment.
0
tion using an excitation light having an intensity of In view of this, as a method of simultaneously
11 nW, decreased to an I/I value of about 1.5 due to achieving lengthening of the recording storage period
0
the writing operation using an excitation light having and shutting out the effect of the surrounding envi-
an intensity of 1,370 nW. Further, thereafter, when a ronment, it is necessary to study measures such as
writing operation was carried out in the same area providing a protective layer on top of the coated thin
with an excitation light intensity of 11 nW, the fluo- film of nanoparticles.
rescence intensity increased again up to an I/I value Further, in this device, improvement in the S/N
0
of about 3.0. This fluorescence intensity of an I/I ratio of the fluorescence intensity is directly related
0
value of about 3.0 due to an excitation light having an to achieving multiple levels in multiple-value
intensity of 11 nW and the fluorescence intensity of recording. Since there are factors that are causing
an I/I value of about 1.5 due to an excitation light deterioration in the S/N ratio, such as the processing
0
having an intensity of 1,370 nW can be recorded problem that the nanoparticles are not coated uni-
repeatedly (Fig. 32.4). formly, and the problems in the apparatus, such as
From the above result, it is shown that the fluores- vibrations during the writing and read-out opera-
cence intensity that is recorded once can be changed tions, the recording capacity is expected to be
to a newly recorded value by irradiating with an increased greatly by solving these problems.
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